Laser microfabrication is currently one of key technologies for manufacturing various kinds of microdevices and microsystems. Additionally, three-dimensional (3-D) laser microfabrication is getting more important and more desirable for integrating functions and miniaturizing the size of devices and systems. The present paper describes a variety of 3-D laser microfabrication based on chemical vapor deposition (CVD), ablation modification and lithography. One of the hottest topics in this field is fabrication of 3-D microstructures embedded in transparent materials by multiphoton absorption process using femtosecond laser. Advantages of 3-D laser microfabrication is also discussed by comparison with competitive techniques like mechanical machining, electron beam processing and ion beam processing.

Laser microfabrication processes are finding an increasing number of commercial applications, and, in turn, the promise of commercial application now motivates most current process and hardware development efforts. Consequently, it is important for those working the microfabrication field to consider the commercial as well as the technical issues relevant to their work. The pervasive drive toward miniaturization seen in a wide range of electronic and mechanical devices offers many opportunities for the laser microfabrication specialist to have a significant impact on technology that ultimately appears in the commercial marketplace. Identifying these opportunities requires a basic understanding of market forces, competing and complementary technologies, and cost issues as well as an appreciation of the implications of miniaturzation trends. A broad overview of ongoing developments in the microelectronics and microsystems fields suggests a long-term need for ever-improving laser microfabrication tools and processes.

Silica glass is an important material in optics and optoelectronic devices because of its outstanding properties, such as transparence in a wide wavelength range, strong damage resistance for laser irradiation, and high chemical stability. In order to develop simpler processes of micro-fabricating silica glass using a pulsed laser, we have investigated a one-step method to microfabricate a silica glass plate using laser-induced backside wet etching (LIBWE) upon irradiation with ns-pulsed UV lasers. Two laser irradiation systems were employed for the fabrication; (1) mask projection system with a KrF excimer laser and (2) Galvanometer-based point scanning system with a single mode laser beam from a diode-pumped solid state laser at 266 nm. We have succeeded in a fine micro-fabrication of silica glass surface. In addition, a novel approach in the fabrication of microarrays of dye and protein on fused silica plates using LIBWE technique was achieved. The surace of fused silica plates was initially pre-coated using trimethoxysilane self-assembled monolayers (SAMs), then etched using the LIBWE method to obtain the desired microstructures on the plate surface. Using this technique, the SAMs on the non-irradiated areas were able to survive the LIBWE process, and were used as templates for the subsequent deposition of dye molecules, proteins, or polystyrene microbeads via chemical bonding or physical adsorption.

Challenges for laser-induced structure ordering from nano-particles to single-crystal patterning in glasses are described. Transparent crystallization in glass must be the best material solution to obtain novel functional glasses with a permanent second-order optical nonlinearity. We focus on the new functions created by structure ordering in glass by means of laser micro-fabrication for space-selected crystallization. Two topics in our recent experimental results of laser-induced structure ordering in glass will be presented as follows: (1) UV-laser induced structure ordering of nano-particles in tellurite-based glasses and possible photonic integrated circuits with innovative minute scale. (2) Single crystalline patterning by atom heat laser processing in Sm-doped glasses for optical waveguides with second-order nonlinearity.

The use of fs lasers to directly write phonic structures inside a glass has great potential as a fabrication method for three-dimensional all-optical integrated components. The ability to use this technique with different glass compositions --specifically tailored for a specific photonics application -- is critical to its successful exploitation. Consequently, it is important to understand how glass composition effects waveguide fabrication with fs laser pulses and how different glasses are structurally modified after exposure to fs laser pulses. We have used confocal laser spectroscopy to monitor the changes in glass structure that are associated with waveguide fabrication. Using a low power continuous wave (cw) Ar laser as excitation source we have measured both Raman and fluorescence spectra of the modified regions. Raman spectroscopy provides us with information on the network structure, whereas fluorescence measurements reveal the presence of optically active point defects in the glass. In this paper we review our work on fs-laser fabrication and characterization of photonic structures in glass and discuss the effect of glass composition on processing parameters and structural modification.

Recently we found that titanium ions in glass are effective to reduce the ablation threshold in the UV laser irradiation. In case of Nd:YAG fourth harmonic generation (FHG, wavelength: 266 nm) irradiation, glass containing titanium ions showed 1/10 times smaller threshold compared with conventional one used for optics or windows. We named this Ti-containing glass Laser Machinable Glass (LMG). In this paper we present some applications made of LMG, a 4x4 planar micro hole array (PMH) for optical fibers alignment, a micro well array for reaction of a small amount of chemicals, and a micro channel used in the bio-chemical field. Using LMG for laser machining, all samples were fabricated precisely without cracking and chipping. We also successfully synthesized new Ti-containing laser machinable glass with thermal expansion coefficient below 40x10^-7 K^-1. The ablation threshold of this low-thermal-expansion glass was about 1.4 times lower than that of Pyrex. Moreover, this glass showed 25 times higher durability to NaOH (pH=10) than Pyrex.

We have performed experiments in which sample coupons of a commercial photostructurable glass ceramic (PSGC) material have been carefully exposed to various photon doses by pulsed UV nanosecond lasers at λ = 266 nm and λ = 355 nm. Following UV laser irradiation, the samples were analyzed by optical transmission spectroscopy to investigate the latent image and identify the photo-induced trapped (defect) state. The irradiated samples were thermally processed and the quenching of this trapped state and the concurrent growth of a spectral band associated with the formation of nanometer-scale metallic clusters was then observed using optical transmission spectroscopy. The results show that exposure at λ = 266 nm generates a defect state distribution that is markedly broader compared with the defect state distribution that is generated via λ = 355 nm excitation. The defect concentration formed with λ = 266 nm radiation is also much larger compared with the defect concentration associated with λ = 355 nm exposure. The results reveal that the metallic cluster concentration saturates with increasing laser irradiance, while the defect state concentration does not saturate. These studies have identified two precursor states of the exposed PSGC material that are tractable via spectroscopic techniques and could be used to refine the laser exposure and thermal processing of PSGC materials.

We have developed a novel lithography technique, which we refer to here as Volume-Change Thermal-Lithography (VCTL), for application to the mastering process in a manufacture of next-generation ultra-high density optical ROM disks. Using a visible laser beam and conventional optics, we have succeeded in fabricating minute dots with diameters of under 100 nm and with interdot spacing far beyond the optical diffraction limit at a practical fabrication speed of 3 m/s. The combination of the temperature distribution induced by a focused laser beam with a Gaussian profile and a specially designed multilayer consisting of TbFeCo and ZnS-SiO₂ was utilized for fabricating the aforementioned nano-structures. A focused laser beam with a Gaussian profile can generate a peak temperature area far smaller than its spot size. TbFeCo and ZnS-SiO₂ undergo mutual diffusion when heated, a result of which is that their volume expands. An incident pulsed laser induces mutual diffusion restricted to the highest heated area. As a result, minute convex structures appear as dots on the sample surface. In addition to fabrication of continuous dot patterns, as a demonstration, small letters with dimensions of approximately 1 μm were drawn by specific dot arrangement, confirming the strong possibility of the technique.

Nanopatterning on the surface of a spin-coated photoresist using a near-field scanning optical microscope (NSOM) is investigated. A cantilever type nanoprobe whose aperture diameter is approximately 100 nm is installed on the NSOM to produce the nanopatterns. The optical near-field at the tip of the nanoprobe is produced by focusing the light from a He-Cd laser on the entrance side of the nanoprobe. The variation of pattern size are examined with respect to process parameters such as laser beam power, scan speed of the nanoprobe, and thickness of the coated photoresist. The linewidth of nanopatterns reduces for decreasing laser power and increasing scan speed. Using this method, about 200 nm size nanopatterns are produced. Fabrication of a two-dimensional nanopattern of arbitrary shape is demonstrated.

Gallium oxide nanofibers were synthesized by reactive pulsed laser ablation of 99.99% pure GaN target in vacuum condition. The nanofibers have been identified to be β-Ga₂O₃ by X-ray diffraction and selected area diffraction. The structure and composition of the as-deposited product were determined by high-resolution transmission electron microscopy and scanning electron microscopy. The β-Ga₂O₃ nanofibers have diameters in the range of 10 - 20 nm and lengths up to tens of microns. Photoluminescence measurements at temperature between 10 K and room temperature show that the nanofibers emit stable and high brightness UV and blue light at 390 nm and 440 nm respectively under the excitation of 325 nm laser source which my find potential applications in one-dimensional optoelectronics nanodevices.

Silver nanoparticles have been fabricated by laser ablation of a silver metal foil in solution. The presence of sodium bis(2-ethylhexyl) sulfosuccinate increases the yield of the nanoparticles and enhances their stability. The optical limiting performance of the silver nanoparticles embedded in a PMMA film is compared to that in an aqueous solution.

We report the optical limiting response of carbon nanoparticle colloids in different organic solvents. The carbon nanoparticles were prepared by Nd:YAG laser ablation of carbon target immersed in ethanol. Optical limiting properties towards 532 and 1064 nm wavelengths were measured with a 7-ns pulsed Nd:YAG laser. Strong optical limiting effect was detected for the carbon nanoparticle colloids within a solvent having low thermal conductivity. The limiting effect at 532 nm is stronger than that at 1064 nm. Possible mechanisms of optical limiting were discussed.

The increasing demand for smaller devices as well as research into novel structures for high density data storage has necessitated the use of advanced nanolithography techniques for fabrication in the sub-100 nm regime. In this paper, nanoscale lines with a minimum full width at half maximum of 20 nm have been achieved, demonstrating resolution of λ/20. Lithography was made by near field scanning microscope (NSOM) in UV photoresist with 120 nm thickness. Second harmonic generation of femtosecond laser was used as light source of NSOM. The lithography results were measured and analyzed by the same tip of NSOM and scanning electron microscopy (SEM). The size of tip aperture used was about 50 nm. The effects of laser energy and writing speed on the size and depth of lines drawn were studied. By controlling these parameters properly, high quality nano-patterning in photoresist would be achieved. The nano-patterning technique will have potential applications in nanodevice fabrication and data storage.

Electrically switchable liquid-crystal-filled optical gratings were fabricated using two-photon three-dimensional microfabrication based on two-photon-induced polymerization (TPIP). A tightly-focused femtosecond pulsed laser beam was used to pattern polymeric grating fringes with a period of 5 μm on glass substrate coated with indium tin oxide (ITO) and a rubbed polyimide liquid-crystal alignment layer. Switchable diffractive devices were prepared by sandwiching a cyanobiphenyl nematic liquid-crystal mixture between a patterned and a blank ITO/alignment layer-coated substrate such that the liquid-crystal director was parallel to the grating fringes. Application of a voltage across the ITO electrodes rotates the director to normal to the substrate surface leading to near index matching of the liquid crystal and polymer fringes and a strong reduction in the diffraction efficiency. These switchable liquid-crystal diffractive devices exhibit a switching contrast ranging from 17 to 100 for the ± 1 diffraction orders for s-polarized light at 3 V_pp. This work demonstrates the utility of TPIP microlithography for producing active micro-optical devices.

Optically driven nanomanipulators with two degrees-of-freedom have been developed by using two-photon microstereolithography. The nanomanipulators are worked by maneuvering their movable component with a focused laser beam. To control the movement just by a single laser beam, the nanomanipulators is attached to a column-like structure named "Optical trapping point." Since the driving performance of the nanomanipulators depends on the shape and size of the optical trapping point, we have optimized the column-like optical trapping point. By the optimization of the optical trap point, the driving frequencies of translational motion and rotational motion were attained to 12 Hz and 120 rpm, respectively. The nanomanipulators also offers the torque on the order of fN to pN. Such optically driven nanomanipulation tools will be widely applied to micro/nano biotechnology and micro total analysis systems (μ-TAS).

Three-dimensional woodpile photonic crystal structures were recorded in films of polymeric photoresists polymethylcrylate (PMMA) and SU-8 films by femtosecond laser microfabrication technique. The fabricated structures consist of periodic arrays of extended elliptical void-channels in PMMA, and of solid elliptical rods of cross-linked polymer in SU-8. Their lattice periods of several micrometers and typical sub-micrometric feature sizes allowed to confirm presence of pronounced photonic stop-bands at infrared wavelengths around 2.0 - 8.0 μm.

We present a flexible microfluidic channel fabrication platform that can be used to develop microfluidic chips. A DPSS (diode pumped solid state) frequency quadrupled (λ = 266 nm, the UV system) Nd:YAG laser and a CO₂ laser (λ = 10.6 μm, the IR system) are compared for their ablation capability on quartz and glass. We have also compared their performance in developing microfluidic chips. The resultant surface quality, including microcracking, debris, and distortion, is examined by SEM and a surface profiler. In these systems, users design microfluidic patterns by commercial software. The pattern is then transferred to a CNC stage for trenching. The microfabrication process can be completed in several minutes. Without the need to fabricate photomask for patterning, the development time can be reduced from weeks to hours. In addition, the substrate size is not limited by the dimension of the photomask. Asymmetric trenches demonstrating the machining capability of these systems have been fabricated by these systems. The minimal feature for the IR system and the UV system is 140 μm and 5 μm, respectively. These systems are very powerful for rapid glass microfluidic chip development.

We have investigated microfabrication of inorganic transparent materials using laser plasma soft X-rays with the diffraction limit of 10 nm. As a soft X-ray source, we used Ta laser plasma soft X-rays, whch has a light emission band at around 10 nm. A SiO₂ film was confirmed to have absorption band in the soft X-ray region. Micromachining a quartz plate was demonstrated by irradiation with focused soft X-rays and pulsed 266 nm Nd:YAG laser light. The quartz plates are ablated smoothly at 85 nm/shots. It is found that more than 40% of 266 nm laser light is absorbed by the quartz plates just after soft X-ray irradiation at room temperature. Thus, it is shown that a transient state such as an X-ray generated exciton (X-ray exciton), which have absorption band in UV region, are generated by soft X-ray irradiation. The micromachining technique (X-ray exciton method) can utilize the high space resolution of soft X-ray and the high energy density of conventional UV/visible laser light. Further, we found that a variety of materials such as SiO₂, LiNO₃, Si, CaF₂, LiF and Al₂O₃ are ablated smoothly by irradiation of the focused laser plasma soft X-rays without 266 nm laser light.

We have investigated about machining of glass plates by a UV laser, a nanosecond FHG Nd:YAG laser. Laser wavelength was 266 nm and pulse width was about 4 - 6 ns. Repetition rate of the laser pulse was up to 30Hz. Borosilicate glass plate of 1 mm thick was irradiated by laser pulse in air. An X-Y axis precision trnaslation stage was used to change the laser irradiation spot on the glass surface. The spot size of focusing beam at the glass surface was varied by changing the distance between the glass and a focal lens. Focal position of the focal lens was determined by measuring burn patterns on thermo-sensitive paper as a function of distance between the lens and the paper. When the glass plate was placed at the focal point, radial cracks occurred on the surface. When the glass plate was moved toward the lens by 0.7 mm, ablation still took place and provided good quality groove on the surface with no significant cracks. The cross section of the groove was conical for slower scanning speed while it became shallow dip with rather flat bottom for faster scan speed. The grove depth increased linearly as the laser fluence increased.

Glass-ceramics (GCs) usually have glass structure doped with microcrystals that are responsible for main properties: mechanical, chemical, optical, etc. As for optical properties, GCs are non-optical materials due to a strong scattering in the visible range. By now different laser technologies for modification of structure of GCs structure have been developed. Heating of GCs with the use of a laser radiation transforms crystalline phase in to glassy. It results in a change of following physical and chemical properties of the irradiated area as density, volume, viscosity, hardness, transparency, refraction, etc. The most important thing is that optical transparency of GCs drastically increases in the visible and near IR range due to the appearance of a new glassy structure. Variation of laser treatment conditions (power, exposure, wavelength from IR to UV) as well as selection of composition of GCs allows to control mentioned characteristics. We have investigated two compositions of GCs with crystalline phases of TiO₂-SiO₂ (Sitall ST-50) and Li₂O-SiO₂ ("Fotoform"). The change of refractive index and surface relief has been used as the first step for fabrication of optical elements. The second stage was a chemical processing including an ion exchange technique (Li↔Na, K, Rb, for "Fotoform") and etching of irradiated and non-irradiated areas. Crystalline and glassy phases have different diffusion coefficient and rates of etching. It allows to modify the refractive index and the surface relief of optical elements. The other important feature is a difference in the macroscopic volumes of ordered-disordered phases which can be used to produce some surface reliefs etc. As a result of above mentioned rsearch mini- and micro-optical components based on two GCs have been fabricated and demonstrated: lenses and lens arrays, waveguides and other waveguiding components, diffractive gratings, integrated diaphragms etc.

Laser-based mass production of micro structures may not be suitable in many cases because it is a serial process: devices are fabricated one by one only. Replication techniques for fabricating nano/micro structures have been investigated and developed for a long time and in our work, we present replicating micro structures in polymers using laser fabricated glass-ceramic stamps. A micro stamping process applying heat and pressure, also referred to as hot embossing, can replicate micro structures on polymer surfaces. By reforming thermoplastics, micro features can be transferred to polymer surfaces. Hot embossing normally employs metal and or silicon stamps. In this work, we use a glass-ceramic stamp which can be easily and quickly fabricated with a laser-based pattern transferring technique. In addition, a micro stamping device has been designed and developed for this process. Many micro structures such as micro channels, capillaries, and micro diffusers are produced and the advantages of this process are discussed.

High-temperature-resistant laser-induced Bragg gratings were formed in Ge-B-SiO₂ thin glass films fabricated by the plasma enhanced chemical vapor deposition method. Such gratings were induced by exposure of an interference pattern with KrF excimer laser and subsequently annealing at 600°C. The SEM observation of the grating after HF etching revealed that the origin of the grating was the periodic precipitation of crystalline 20 - 40 nm-diameter Ge nanoparticles. Nanoparticles precipitated predominantly in the unirradiated region after laser-induced refractive index change completely erased after annealing up to 500°C. The maximum value of refractive index modulation Δn was 6.8 x 10^-3 at 632.8 nm, which corresponds to the Δn nearly 10 times as large as that before annealing. A channel waveguide with high-temperature-resistant-grating exhibited high diffraction efficiency and excellent thermal stability.

We discuss our recent experiments that aim at fabrication of optical microsphere resonators and methods for their quality estimation. First, free space laser melting technique (FSLMT) was investigated. Different regimes of laser action and its corresponding results were discussed. Secondly, we fabricated optical microsphere resonators of different sizes and optical glasses (including active glasses) using FSLMT. Whispering gallery modes (WGMs) in fabricated microsphere resonators were then observed in microspheres' fluorescence spectrums, the free spectral ranges were in good agreement with diameters of microspheres. Furthermore, WGMs of microsphere resonators were excited by an optical fiber-taper coupler to assess the microspheres' Q-factor. Applications of optical microsphere resonators such as microlaser, simple block for studying emission and nonlinear optical effects were demonstrated.

Microlenses were formed directly on a surface of a glass plate by using CO₂ laser. This method has the merit of complete dry processing and presents simple way of microlens fabrication. We discuss about the formation process and mechanism through the characterization of irradiation parameters and the glass composition. When the surface of a glass plate is heated locally to a working point of the glass material by a focused CO₂ laser beam, a microlens is formed owing to surface tension. It was found possible to fabricate microlens easily placed at different focal position by controlling a laser power and an irradiation time. The volume of the fabricated microlens was found to be dependent on laser irradiation energy (laser power x irradiation time) and irradiated position. When a Corning 7059 glass plate was used, a convex microlens was obtained at the energy density smaller than ca. 100 (μJ/μm²).

Cutting and sealing methods of quartz and borosilicate capillary glass-tube using CO₂ laser have been investigated. Conventional cutting and sealing glass tube have been done independently from each other. In this study, cutting and sealing processes of glass tube with 1.4 mm outer diameter and 0.25 mm thickness are done simultaneously. Key parameters of laser glass-tube cutting and sealing are laser power, laser spot-size, exposure time and rotation speed of glass tube. Also, the gas pressure-difference between the inside and the outside of glass tube plays a pivotal role in determination of cutting quality. Laser power required for sealing of quartz tube is about 3 times higher than that of borosilicate tube. However, the cutting power of borosilicate tube is slightly higher than that of quartz tube. A clean cut requires 2 or 3 times of rotation within 0.7 sec exposure-time. A proper spot-size of laser should be irradiated on the surface of glass tube, to obtain an enough melting volume for sealing. Differences of cutting and sealing quality beween quartz and borosilicate tubes have been presented in this article.

During the past years ultrashort pulse lasers have gained a lot of interest for the direct writing of photonic structures in transparent media. This technique allows to produce true three-dimensional optical structures and is applicable to many different glasses as well as to crystalline media. Although the mechanism responsible for the refractive index changes is still under discussion, various photonic structures, ranging from low loss optical waveguides to couplers, three-dimensional splitters and also active waveguides, have been realized. In this presentation, an overview of the recent advances in the ultrafast direct writing of photonic devices in different glasses as well as crystalline media will be given.

Sub-wavelength (1/4*λ-3/4*λ) laser induced periodic surface structures are generated by irradiation of either bulk fused silica and silicon or Er:BaTiO₃ thin films by scanning a tightly focused beam (Θ = 1 μm) of femtosecond laser radiation (λ = 800 nm, t_p = 100 fs) on the surface. The ripple pattern extends coherently over many overlapping laser pulses parallel and perpendicular to the polarization of the laser radiation. The dependence of the ripple spacing on the spacing of successive pulses, the direction of polarization and the properties of the material is investigated. The evolution of the ripples is investigated by applying pulse bursts with 1 - 20 pulses. The development conditions of the stuctures are specified and possible mechanisms of ripple growth are discussed.

Femtosecond laser is under intense study as a new laser processing tool which can induce refractive index change and color center, etc. inside of transparent materials. Here, we report on the first observation of the formation of polarization-dependent nano-grating by irradiation of only single femtosecond laser beam inside silica glasses. This nano-grating was formed by the self-organization at intervals of 200 nm of generated oxygen defect in the laser focal point. The direction of nano-grating was controllable by laser polarization direction. Additionally, the periodicity was variable according to the irradiation laser light of energy and pulse number. We proposed a mechanism of this novel phenomenon containing the interference between the laser light (photon) and the generated plasma wave on the focal point.

We report on three-dimensional (3D) holographic recording in As₂S₃ glass using 800 nm wavelength, 150 fs duration pulses. Diffractive beam splitter was used to generate 2 - 5 beams which were then focused for recording by objective lens of numerical aperture NA = 0.75. The recorded 3D hologram was read out by diffraction of 632 nm HeNe laser beam confirming the expected pattern of holograms. The mechanism of photo-darkening and optical damaging of As₂S₃ glass and dielectrics in general is discussed. Two-photon absorption cross-section, σ₂ = 74.6 x 10^-50 cm⁴/s, was determined by transmission for pulses of 150 fs and 800 nm wavelength. Also, it is demonstrated that the optical damage threshold scales as the bandgap energy for the fluorides. Nano-/micro-structuring of As₂S₃ glass by ablation in air will be also demonstrated. High fluence (> 5 J/cm²) irradiation of the 800 nm wavelength, 150 fs duration pulses was used to ablate As₂S₃ glass. Self-organized growth of the fibers, rods, and microsphere-type structures was observed. Composition of the nano-/micro-structured material was close to that of the source As₂S₃ glass (with up to 20% surplus of sulphur in nano-rods). Straight rods as thin as 20 nm in diameter and over 1 μm-long were obtained. Application potential of nano-/micro-structured As₂S₃ glass is discussed.

This paper presents the micro-machining results on optical devices by using Ti:sapphire femtosecond pulsed laser. It has been used successfully for the micro-machining of U-grooves in planar lightwave circuit (PLC) splitter, wedged filber and lensed fiber. U-grooves in PLC splitter is helpful to simplification of the alignment procedure between optical fiber and waveguide in the PLC chip. The insertion loss and the optical return loss of packaged 1 x 8 optical splitter modules which have been presented were less than 11.0 dB and more than 55 dB, respectively. These results also mean that the packaging technique using the passive alignment is excellent and femtosecond pulsed laser micro-machining technique could provide a new PLC packaging technology. The wedged fiber for reduction of reflection loss and the lensed fiber increasing coupling efficiency are also fabricated by laser system. A comparison of direct polishing method with that of laser micro-machining shows that laser technique is more favorable.

We show that permanent optical waveguides can be formed in glasses by photoinduced refractive index change with an ultrashort pulse laser. Waveguides are written by translating the glass sample along the optical axis of a strongly focused laser beam. Both straight and curved waveguides are written in a silicate glass using 800 nm Femtosecond laser pulses. The utility of the Femtosecond writing technique is demonstrated by fabricating optical devices. Y coupler was fabricated in a silica glass using femtosecond laser pulses. Waveguide propagation characteristics and optical losses are also determined.

Heavy metal oxide (HMO) glasses include, among others, compound oxide glasses with high Bi- and/or Pb-oxide content. These materials are very atttractive for photonic applications because they show phonon energies lower than those of silicates or borates, which provides them with an extended transparency interval in the mid infrared (λ ≤ 7-8 μm). This feature makes them specially suitable for infrared transmission applications. In addition, they have high density, a relatively low glass transition temperature, and an excellent chemical and physical stability. However, they show relatively small energy band-gaps (2 - 3 eV) and large linear (n_o ≥ 2) and non-linear refractive indices (n₂ ≈ 10^-19 - 10^-18 m²/W), which makes their processing with ultrashort pulses to become a challenge. This work analyses different issues inherent to the production of waveguides in these materials by direct writing with fs laser pulses. We will show, as an example, the feasibility of writing efficient waveguides in 35PbO • 35Bi₂O₃ • 15 Ga₂O₃ • 15 GeO₂ HMO glass. The comparison of the behavior of this material with glasses showing lower linear and non-linear refractive indices allows to conclude that direct fs-laser waveguide writing with peak powers above the critical self-focusing threshold is feasible. Different means to control the guided mode distribution under this condition are presented.

We report on precipitation, control and erasure of Au nanoparticles inside transparent glasses. Au³⁺-doped glass is first irradiated by an 800-nm femtosecond laser at room temperature and then annealed at various temperatures. Transmission electron microscopy shows Au nanoparticles precipitates near the focal point of the laser beam after the irradiation and successive annealing at temperatures above 450°C. We suggest that multiphoton ionization leads to reduction of Au ions, and subsequent nucleation from a high-temperature annealing results in precipitation of Au nanoparticles. We show that the size of the Au nanoparticles could be controlled by the irradiation conditions, and demonstrate that the precipitated Au nanoparticles could be broken by the second irradiation of the femtosecond laser. The similar phenomena have also been observed in Ag⁺-doped glasses. The observed phenomenon has promising applications for the fabrication of 3-dimensional multi-colored images inside transparent materials, rewriteable optical memory and for integrated micro-optical switches.

We describe the fabrication of 3D microoptics and microfluidics embedded in glass using femtosecond laser direct writing. By integrating the microoptics and the microfluidics, microfluidic dye lasers three-dimensionally embedded in glass have been fabricated for the first time. By pumping the microfluidic laser, in which the microfluidic chamber was filled with laser dye rhodamine 6G dissolved in ethanol, by a frequency-doubled Nd:yttrium aluminum garnet laser, lasing action was confirmed by analyzing the emission spectra at different pumping powers. In addition, by arranging two microfluidic chambers serially in the glass, we built a microfluidic twin-laser which produces an array of two simultaneous laser emissions with one pumping laser. The integration of microoptics and microfluidic in a single glass chip paves the way toward the automatic fabrication of biophotonic chips.

The advantages of ultrafast laser processing of materials include a minimal thermal penetration region and low processing temperature, precision removal of material, and good-quality feature definition. In this paper, fs laser (800 nm, 100 fs) processing of transparent materials at different focus positions and different laser intensities is investigated. Different morphologies are presented and compared. It is found that at controlled laser fluences, both bowl-shape and hump-like microstructures can be produced at the material surfaces. The lengths of the cracks produced inside the bulk material were measured as a function of the focus positions. The physical mechanisms for the formation of different microstructures are discussed. To reduce the patterning size, we employ transparent particles as microlens on the surfaces by self-assembly. Parallel structures in nanometer scale were produced by single fs laser pulse irradiation. These nanostructures change their shapes at different laser energies. The optical near-field distribution around the particle was also calculated according to exact solution of light scattering problem.

Laser drilling becomes of increasing importance when hole diameter is in the range of 10 to 50 μm, for which conventional alternative approaches are becoming difficult and cost inefficient. Furthermore, it is viewed as the technique of choice for a number of composite materials and hard materials which are not readily processed at the microscopic level by contact mechanical tools. We have demonstrated that suitable experimental conditions are capable of producing microholes with record aspect-ratio (up to 600) in pure polymers like PET, PI, PC, PS, PMMA, PEEK, ... For example holes of diameter typically 30 μm can be as long as 18 mm, depth at which the drilling rate is getting nearly zero and the profile stationary. Other materials (metals, ceramics) which can be similarly laser microdrilled do not exhibit such very high aspect-ratio. The mechanisms of the drilling process have been studied in details and an original analytical model has been constructed recently. The various experimental results, obtained with the KrF laser, will be reviewed with emphasis on the parameters leading to formation of good holes with high aspect-ratio. For the application it is also important to note that such high values of aspect-ratio are obtained with regular configuration of the KrF laser giving a standard divergence of 3 mrad. However as shown by the model there is still room for improvement by using a beam with a lower divergence (theoretical limit s 0.2 mrad). Further experimental work is now in progress.

By UV-laser irradiation the refractive index of some polymers can be locally increased in a controllable way. So by mask lithographic methods integrated-optical waveguiding and dispersive structures can be generated in the surface of a planar polymer chip. Thus a polymeric Bragg-sensor component in integrated-optical form was fabricated by the UV-light of an excimer laser. The surface morphology and optical-functional properties of the polymeric Bragg sensor component have been examined especially in dependence on the irradiation parameters and the temperature. The investigations yield the suitability of the Bragg-sensor for the measurements of temperature and deformation. For the realization of a passive fiber-chip coupling for the integrated-optical components a new technology has been developed and tested. The precise control and high-resolution ablation capability inherent in excimer laser machining make it ideally suited for creating grooves for passive alignment of optical fibers to planar channel waveguides.

The ablation of silicone rubber (polydimethysiloxane, [SiO(CH₃)₂]_n) by 157-nm F₂ laser irradiation has been studied. The ablation threshold fluence (F_th) was approximately 140 mJ/cm². The irradiated surface swelled and was modified to SiO₂ for laser fluences below F_th. No carbon contamination was observed in the SiO₂. Above F_th, the surface of etched silicone rubber was structurally well defined and precisely patterned. The chemical composition of the etched surface demonstrated little change. When the silicone rubber was irradiated at laser fluences of nearly F_th, conical structures were formed on the surface. It is supposed that residual carbon photodissociated by laser irradiation initiated cone formation by locally shifting F_th to a higher value. In situ mass spectrometric analysis of gaseous products evolved during F₂ laser irradiation of silicone rubber showed that CH₃ and CH₄ components dominated for laser fluences below F_th, and CO component dominated for laser fluences above F_th. The high photon energy (7.9 eV) of an F₂ laser could photodissociate preferentially weak bonds (Si-C) of silicone for lower laser fluence and almost all bonds (Si-C, C-H, Si-O) of silicone for higher laser fluence.

Microlenses are widely used as components of optical device in LCD display, optical interconnection, scanner and others. It is important to fabricate microlens in any kind of form to satisfy any requirement of optical device. Also, the integration of microlens and optical devices is required to save weight, reduce production cost, and get higher accurate alignment. We have developed a novel method to fabricate spherical plastic microlens using Er:YAG laser beam. In this method, laser beam are shot to the surface of an acrylate resin to form microlens on this surface. In this paper, a method to fabricate cylindrical plastic microlens is proposed. Microlenses are fabricated under several conditions, and the influences of process parameters to geometry of microlens will be discussed.

Surface grating-like ablation with microscopic period (Λ ~ 1-5 μm) is achieved at the surface of polymers with the aid of the KrF laser patterned with a mask projection technique using a precision imaging lens. The ablated patterns can be controlled with a submicron accuracy in most cases on smooth polymer surfaces. Prediction of these patterns can furthermore be made with the aid of theoretical models combining ablation curves, intensity profiles and hydrodynamic flow. We further demonstrate that by using harmonic filtering the grating period can be divided by a factor 2 thus leading to a convenient resolution enhancement. This improvement can be achieved by two experimental approaches. One is by changing the defocus and the other is the removal of low level orders (0 and ± 1) of the Fourier components of the image beams. Resulting grating patterns with doubled spatial frequency will be presented for a number of polymeric materials (AFM, SEM). It reveals to be a good method to overcome the theoretical limitations due to numerical aperture of the precision lens which prevent the transfer of details in the image by erasing the high spatial frequencies. This interesting optical set up and method offer also the advantage of a large working distance above the sample surface which is compatible with irradiations in vacuum and liquid phase.

Near-infrared (NIR) 80 MHz nanojoule femtosecond laser pulses of low sub-nanojoule and nJ pulse energies in combination with focusing optics of high numerical aperture can be used as versatile multiphoton tools in nanobiotechnology and nano/micro-medicine. Novel diagnostic applications include gene imaging by multiphoton multicolor FISH (MM-FISH) and high-resolution multiphoton tomography of skin as well as tissue engineered cardiovascular structures based on two-photon autofluorescence excitation and second harmonic generation (SHG) of endogenous biomolecules. Using high-intense (10¹¹ - 10¹² W/cm²) 80 MHz femtosecond laser beams, non-invasive targeted transfection of mammalian cells with DNA can be realized by creation of highly localized membrane perforations. Nanosurgery can be performed by optical knocking out of intracellular and intratissue structures. Potential applications include gene and cancer therapy, eye and brain surgery as well as optical engineering of single DNA molecules as key elements in bionanotechnology.

The present paper will discuss the influence of the processing parameters on the characteristics of titanium models built by Selective Laser Melting. The microstructure and the fatigue strength of the three dimensional titanium models formed by Selective Laser Melting with an Nd-yttritrium-aluminum-garnet (YAG) pulsed laser are investigated. In order to increase the wear resistance of titanium models, surface alloying via laser-gas-nitriding (LGN) is applied. The mechanical properties of the models built by laser forming are adequate for fabrication of dental implants.

In the production of micro devices the surface properties become more and more important for chemistry, biotechnology and medical technology with respect to wetting properties and chemical composition of the surface. Typical applications are implants as well as micro fluidic systems or miniaturized devices for DNA- and proteome analysis (biochips). In this paper newly designed laser technologies based on UV-laser treatment of polymers for surface processing are described to manipulate wetting properties, cell growth and immobilization of functional molecules with high spatial resolution. Depending on the processing parameters and used polymers either hydrophobic or hydrophilic properties can be enhanced (i.e. laser induced lotus/anti-lotus effect). Enhanced roughness and changes of the chemical composition have also influence on cell growth on polymer surfaces. Thus guiding aids for cells e.g. on medical implants can be generated by laser irradiation. Due to photo oxidation processes while UV-treatment in air, functional groups are created that are suited for covalent bonding of (bio)moelcules onto the surfaces. A second process for the locally selective immobilization of anchor molecules based on azide functionalized templates suitable for further modification steps is presented by means of irradiating polymers under solutions of these linkers.

We propose new application of a pulsed deep-UV laser to processing biological macromolecule crystals. Single crystals of model protein, hen egg white lysozyme, were processed by deep-UV laser irradiation at 193 nm and 266 nm. Desired laser ablation was achieved using the 193-nm light source. A crystallinity of the processed crystals was evaluated by X-ray diffraction pattern recording. The crystal diffracted beyond a 1.9 Å resolution, which was the same as that of the as-grown crystal obtained under identical growth conditions. In addition, we observed that a diffraction pattern from a cracked protein crystal was considerably improved by eliminating the damaged section with the 193-nm laser ablation. A processing tool for protein crystals currently employed, such as a micro needle or knife, suffers from low reproducibility and poor accuracy. The technique using deep-UV laser pulses will be a powerful tool for processing very fragile protein crystals.

The article presents the results of macroscopic examination of adhesion of hydroxyapatite layers deposited by the PLD method on nitrided substrates made of Ti-Al-4V alloy. The layers were deposited by means of the ArF laser, in vacuum at p ~ 3 x 10^-5 Torr, after deposition layers were annealing during the period of 90 minutes, at the temperature of 600°C. The research of the deposited layer topography and the topography of tested layers were carried out by means of the atomic force microscope. The comparative examination showed that the mechanical resistance of the deposited layers depends not on their adhesion to the substrate, but on the cohesion of the deposited material. The most damage-resistant layers proved to have the thickness of the order of several hundred nanometers, as they are still influenced by the forces of adhesion to the substrate. The plasticity characteristic for such layers is similar to the plasticity of the substrate. The deposited layers, both amorphous and polycrystalline were characterized by columnar structure.

The joining processes in watch manufacturing industry are today still dominated by conventional joining techniques like press fitting or crimping. Laser beam micro welding provides consistent joining and high flexibility. Different parts and even different metals can be joined in a non-contact process. The application of a relative movement between the laser beam and the part to be joined at feed rates of up to 60 m/min produces weld seams with a length from 0.6 mm to 15.7 mm using a pulsed Nd:YAG laser with a pulse duration of up to 20 ms. Due to the low energy input, typically 1 J to 6 J, a weld width as small as 50 μm and a weld depth as small as 20 μm have been attained. This results in low distortion of the joined watch components. Since the first applications of laser beam micro welding of watch components showed promising results, the process could be further enhanced using the SHADOW welding technique. Aspects of the technique such as tensile strength, geometry and precision of the weld been improved. Within the scope of this paper this new welding process will be explained and several examples of joined watch components will be presented with respect to fundamentals and the sustainable implementation of the SHADOW welding technique into watch manufacturing. New fields of applications for joining different materials such as steel to brass or steel to copper for electrical interconnects will be discussed. Here the SHADOW welding technique offers new possibilities for the combination of good electrical properties of copper with high mechanical stiffness of steel. The paper will give a closer look to micro joining applications especially using the SHADOW welding technique. Basics of the process as well as its application on dedicated examples will be shown for small parts such as axis-wheel combinations.

The diode pumped thin disk laser found large attention, recently. This relatively new laser concept combines the high efficiency and the good focusability of CO₂-lasers with the short wavelength of YAG-lasers. The short wavelength enables fiber guided beam delivery and brings along advantages for the process such as higher absorptivity in metals and lower sensitivity to laser induced plasma. Due to its good focusability the thin disk layer is best suitable for laser beam micro welding of thin metal sheets. Up to now, this field of applications was reserved for pulsed laser systems. This contribution presents results of high speed micro welding of thin metal sheets with the thin disk laser. The advantages of high beam quality will be discussed in detail. As an example, with a focal spot of 100 μm keyhole welding was performed at travel speeds up to 40 m/min with best quality without any humping. The promisng results demonstrate the great potential of the thin disk laser in the field of micro welding of thin and ultra thin metal sheets.

This paper deals with parameter optimization and online monitoring of laser spot welding (LSW). Using Nd:YAG laser, a wide range of experiments regarding the welding process have been carried out for both successful and failed welds. The typical failures appearing during packaging of surface mounted devices (SMDs) on flexible printed circuits (FPC) include gaps, a loss of connection between the welded components, and damage of the printed circuit boards. A flip-flop device called SO16 and lead frames as two components of widely used SMDs were packaged on FPCs in the experiments. The reproducibility of the weld quality for SO16 (FeNi) is greater than for lead frames (CuFe2P); this points out the difficulties appearing during copper or copper alloy welding. However, a correlation between the weld quality and the detected emission signals recorded during the weld process has been found for both components. The detected signals of the optical process emission for successful welds depict identical characterisics which are divided into three relevant signal phases. Changes in the signal characteristics, especially in these phases, imply information about the weld quality. While monitoring the welding processes for both components are possible, the detected signals for SO16 are less sensitive to process variations compared to those for lead frames. Based on spectral analysis, the intensity of the detected emission due to SO16 welding is slightly higher than the intensity due to lead frames welding.

EUV lithography is scheduled on the international technology roadmap for semiconductors (ITRS). In order to introduce the EUV light source into the production lines, EUV light sources having an average power of more than 100 W at 13.5 nm are needed. Such EUV light sources have been under development by using the laser-produced plasma (LPP) or the discharge-produced plasma (DPP). In the case of Sn LPP, the efficiency is several times higher than that of Xe LPP, but the problem of debris generation that limits the lifetime of the optics in the lithographic system is serious. The mechanism of debris generation is considered to be splashes of a melted surface by rapid heating of the sub-surface within a depth of about 100 nm. So we have suspected that the nano-particles with a diameter of less than 100 nm produce no debris, because the sub-surface can not be produced within such a small particle. In this study, we developed nano-structured SnO₂ targets and investigated the emission characteristics of EUV light from CO₂ laser produced plasma with those targets.

A bonding process between tape-carrier package and a glass panel with anisotropic conductive film (ACF) is tested preliminarily by making use of high power diode laser as a heat source for curing. Laser transient thermal simulation was also carried out to analyze thermal response of the assembly process for a package using ACF. Bonding layers consist of polyimide film, copper bump, ACF, ITO and glass plate. The results from modeling of process and from optical properties of layers showed that heat absorbed from polyimide film surface and ACF layer is dominant source of curing during laser illumination. The temperature on ACF layer goes up to 180°C within 1 sec. The temperature in depth shows a decrease of about 17% from polyimide film surface to the bottom of glass plate, but a constant temperature in ACF layer. It is confirmed by experiment that laser should be irradiated periodically in order to maintain the temperature in the range of 175 - 185°C for curing. New ACF bonding processes by making use of high power diode laser are proposed.

In the present study, bead-on-plate specimens of 1-mm sheets of austenitic and duplex stainless steels were fabricated by laser penetration welding with a 2.5-kW CW Nd:YAG laser. The galvanic corrosion behavior of laser-weldment (LW) against as-received (AR) specimens with an area rato of 1:1 in 3.5% NaCL solution was studied by means of a zero-resistance ammeter. The free corrosion potentials of as-received specimens were found to be considerably higher than those of laser weldments, indicating that the weldments are more active and always act as anodes. The ranking of galvanic current densities (I_G) of the couples in ascending order is: AR S31603-LW S31603 < AR S31803-LW S31803 < AR S32760-LW S32760 < AR S30400-LW S30400. For the galvanic couple between AR S30400 and LW S30400, the I_G is the highest (78.6 nA/cm²) because large amount of δ-ferrite in the weld zone acts as active sites. On the other hand, the I_G of the galvanic couple between AR S31603 and LW S31603 is the lowest (-26 nA/cm²) because no δ-ferrite is present after laser welding. The recorded I_G of all couples revealed constantly low values (in the rnage of nA/cm²) and sometimes stayed negative, which indicated polarity reversal.

The introduction of real time controlled power supply technique made it possible to considerably improve welding feasibility, welding seam quality, and the reproducibility of welding. Even welding jobs that are challenging because of the metallurgical properties of the materials have become possible thanks to the method of a defined control of the heat input and of the influence of melting pool dynamics. Furthermore new process tehniques like SHADOW and closed loop feedback power controlled spot welding open up new fields of application for pulsed Nd:YAG lasers.

The most evident trend in electronics production is towards miniaturization. Regarding the materials involved, another trend can be observed: intelligent combinations of different materials. One example is the combination of copper and aluminium. Copper is the material of choice for electronic packaging applications due to its superior electrical and thermal conductivity. On the other hand, aluminium offers technical and economical advantages with respect to cost and component weight -- still providing thermal and electrical properties acceptable for numerous applications. Especially for high volume products, the best solution often seems to be a combination of both materials. This fact raises the question of joining copper and aluminium. With respect to miniaturization laser micro welding is a very promising joining technique. Unfortunately, the metallurgical incompatibility of copper and aluminium easily results in the formation of brittle intermetallic phases and segregations during laser welding, thus generating an unacceptable quality of the joints. This paper presents investigations on enhancing the quality during laser micro welding of copper and aluminium for applications in electronics production. In order to eliminate the formation of brittle intermetallic phases, the addition of a filter material in form of a foil has been investigated. It can be shown that the addition of pure metals such as nickel and especially silver significantly reduces the occurrence of brittle phases in the joining area and therefore leads to an increase in welding quality. The proper control of the volume fractions of copper, aluminium and filler material in the melting zone helps to avoid materials segregation and reduces residual stress, consequently leading to a reduction of crack affinity and a stabilization of the mechanical and electrical properties.

Sealed CO₂ lasers at <500 watts power are widely used for cuttng and drilling, but their welding performance is less well known. The welding trials reported here address this by identifying welding performance for certain widely used ferrous and non-ferrous materials. Welds were made at a fixed average power and a range of laser parameters over a range of weld speeds. Conventional metallographic techniques were used for assessing weld dimensions and weld quality.

LSM and annealing heat treatment on 304 stainless steel resulted in microstructures with high frequency of low ∑ CSL boundaries defined by the coincidence site lattice (CSL) model, especially, twin boundaries (∑3). The maximum frequency of the low ∑ CSL boundaries could be 88.6% under optimal processing conditions: 947°C and 28h. The high fraction of the low-∑ CSL boundaries led to a high corrosion resistance to intergranular corrosion.

It has reported that a waste of an electronics substrate including lead and its compound such as 63Sn-37Pb has polluted the environment with acid rain. For that environment problem the development of lead-free solder alloys has been promoted in order to find out the substitute for Sn-Pb solders in the United States, Europe, and Japan. In a present electronics industry, typical alloys have narrowed down to Sn-Ag-Cu and Sn-Zn lead-free solder. In this study, solderability of Pb-free solder that are Sn-Ag-Cu and Sn-Zn-Bi alloy was studied on soldering using YAG (yttrium aluminum garnet) laser and diode laser. Experiments were peformed in order to determine the range of soldering parameters for obtaining an appropriate wettability based on a visual inspection. Joining strength of surface mounting chip components soldered on PCB (printed circuit board) was tested on application thickness of solder paste (0.2, 0.3, and 0.4 mm). In addition, joining strength characteristics of eutectic Sn-Pb alloy and under different power density were examined. As a result, solderability of Sn-Ag-Cu (Pb-free) solder paste are equivalent to that of coventional Sn-Pb solder paste, and are superior to that of Sn-Zn-Bi solder paste in the laser soldering method.

We propose CO₂ laser-produced plasma as the extreme ultraviolet (EUV) light source for future optical lithography. The laser beam from a transversely-excited atmospheric (TEA) CO₂ laser (4 J, 50 ns FWHM) was focused on a Xe gas target and a Xe cryogenic target to generate EUV radiation around 13.5 nm. The EUV pulse of about 100 ns in FWHM was measured 50 ns after the CO₂ laser irradiation. The EUV spectra were measured by an X-ray CCD camera with a transmission grating spectrograph (TGS). A characteristic EUV spectrum was observed from CO₂ laser produced Xe plasma. The EUV energy was measured by a Flying Circus II detecting system and an output energy of 3 mJ/pulse and a conversion efficiency of about 0.1% per 2π sr at 13.5 nm (2% B.W.) were obtained with Xe targets. These values are comparable to those of YAG laser-produced Xe plasma, indicating the potential scalability of the EUV light source using a CO₂ laser produced plasma.

The main technological challenge of a future extreme ultraviolet (EUV) light source is the required average power of 115W at the intermediate focus. High repetition rate laser produced plasma (LPP) sources are very promising to face this challenge. We report the current status of the laser produced plasma light source system under development at EUVA. The system consists of the following main components: The plasma target is a liquid xenon jet with a maxium diameter of 50 micrometer and a velocity of more than 35m/s. A Nd:YAG laser oscillating at 1064 nm produces the plasma. The laser is a master oscillator power amplifier (MOPA) configuration with a maximum repetition rate of 10 kHz and an average power of 1 kW. The EUV system currently delivers an average EUV in-band power of 4 W (2% bandwidth, 2π sr) having a stability of 0.54% (1σ, 50-pulse moving average). In order to evaluate a further increase of the repetition rate, xenon jet characteristics and EUV plasma images have been investigated at 10 kHz. In addition, a conversion efficiency of 0.74% (2% bw, 2π sr) has been obtained at low repetition rate operation. This paper presents the progress of our LPP light source development.

We present a source of high power femtosecond pulses at 1550 nm generating compressed pulses at the end of a single mode fiber pigtail. The system generates sub 35 femtosecond pulses at a repetition rate of 50 MHz, with average powers greater than 400 mW. The pulses are generated in a passively modelocked, erbium doped fiber laser, and amplified in a short, erbium doped amplifier. The output of the fiber amplifier consists of highly chirped picosecond pulses. These picosecond pulses are then compressed in standard single mode fiber. While the compressed pulses in the SMF pigtail do show a low pedestal that could be avoided with the use of bulk-optic compression the desire to compress the pulses in SMF is motivated by the ability to splice the single mode fiber to a nonlinear fiber, for continuum generation applications. We demonstrate that with highly nonlinear dispersion shifted fiber (HNLF) fusion spliced directly to the amplifier output, we generate a supercontinuum spectrum that spans more than an octave, with an average power 350 mW. Such a high power, all-fiber supercontinuum source has many important applications including frequency metrology and biomedical imaging.

Laser materials processing has been used increasingly over the wide area of electronic industries, especially for drilling microvias in printed circuit boards, and poly-silicon annealing for thin film transistor of liquid crystal display. Intensity distribution of laser beam is usually a non-uniform gaussian profile. Therefore, the demand for uniform intensity distribution is rising rapidly in some applications of heat processing. To obtain higher uniformity, beam homogenizer of a diffractive optical element (DOE) has recently been developed and introduced to some promising applications. Through the improvement of optical design algorithms and micro-fabrication techniques of a phase pattern of DOE, it becomes possible to convert a non-uniform gaussian distribution not only into a simple distribution like a square and a line but also into a complicated distribution like a distribution of printed circuit pattern. In this study, we introduce a design and fabrication result of beam shaper of DOE that can convert a gaussian distribution into the distribution of a printed circuit pattern, and present the possibility and the point at issue of new laser material processing by using such optics.

A model is developed for the carrier induced refractive-index change in Quantum-well (QW) lasers which affects different mechanisms. The model is based on Artificial Neural Network (ANN) which provides a powerful approach for setting up a complex non-linear model. Different algorithms are tried and tested for different injection current levels. Both the training and the test results for refractive-index change are in very good agreement with the experimental findings reported elsewhere.

In this study. optical carrier and data, which is coining from the 1550 am. CW laser-diode is modulated by using an external optical modulator. The noise that is obtained from the Gaussian white noise source is added to the modulated signal with the help of optical combiners. This combined signal is inputted to the Rarnan Amplifier and the data is transmitted in a 80 kin. fiber optic transmission system. The system is implemented by using chaotic communication tecirnique and the chaotic signal is obtained out of laser diode. Non-return to zero (NRZ) network system is selected in the design.

A measurement interferometer available for wafer stage metrology of lithography has been investigated by means of resolution-extending of optical subdivision based on commercial interferometers. Factors that determine the accuracy, linearity and repeatability of nanometer-scale measurements of displacements exceeding hundreds of millimeters and of target velocities exceeding hundreds of millimeters per second are also discussed.

We have developed a room-temperature fabrication process for β-FeSi₂ microprecipitates through the active use of droplets generated by pulsed laser deposition. The droplets generated by KrF excimer laser ablation of an α-FeSi₂ metallic target were characterized by micro-Raman spectroscopy with a spatial resolution of 1 μm and X-ray diffraction measurements. As a result, it was confirmed that the micron-sized droplets precipitated as the β-FeSi₂ semiconducting phase on silicon and silica glass substrates maintained even at room temperature, whereas the rest of the deposited film was amorphous. It was also found that films containing a high density of β-FeSi₂ microprecipitates exhibited 1.55 μm photoluminescence at low temperature after annealing at 800°C for 6 h in an argon atmosphere.

Thin films of high-k materials praseodymium oxide (Pr_xO_y) and hafnium oxide (HfO_x) were deposited on silicon (100) surfaces by pulsed laser deposition (PLD), using the third harmonic of a Nd:YAG laser. The two materials are compared with respect to their morphology, in dependence on the substrate temperature during deposition, and their chemical composition and crystalline structure, in particular at the interface. The films of both oxides exhibit a grainy structure when deposited at substrate temperatures below 750°C, with the grain size increasing from ≈ 40 nm at room temperature to ≈ 100 nm at 750°C. However, the Pr_xO_y films are much more uniform than hafnia, the latter exhibiting increasingly larger holes, reaching several nm into the silicon substrate. For a substrate temperature of 900°C, the film morphology for Pr_xO_y completely changes to much larger crystalline areas, while for HfO_x the role of holes in the film becomes substantial. Also, the interface chemistry is significantly different for both materials: a silicate formation for Pr_xO_y and a rich abundance of SiO₂ and a silicide for hafnia. Finally, our Pr_xO_y-films exert compressive stress on the substrate, for HfO_x-films tensile stress is observed which, however, may also result from interfacial SiO₂.

An insight into surface chemical reactions responsible for organometallic vapor phase epitaxial growth of ZnSe under alternate supply of diethylzinc and dimethylselenium was provided by findings in laser-assisted free-radical doping experiments. Based on ab initio molecular orbital analyses, atmosphere-sensitive characteristics of the ZnSe growth were attributed to differences in the pathways and the corresponding adiabatic potential barriers between diethylzinc chemisorption onto hydrogen- and methyl-terminated Se-stabilized ZnSe surfaces.

Ion-current difference measurement by light intensity modulation (ICD) is introduced as a convenient method to determine the number flux of netural free radicals produced by photo-deionization of a negative ion beam for the purpose of surface-reaction-selective device processing. The ICD setup developed in this study exhibited the high precision and the high sensitivity under the experimental condition that the beam kinetic energy of the neutral free radicals was higher than 10 keV.

This paper describes a new growth method of ZnO nano-rods. Firstly ZnO nanoparticles were synthesized in an oxygen and He background gas by laser ablation. These nanoparticles were used to deposit nano-structured-ZnO thin films. Under an optimized deposition conditions, ZnO nano-rods with a diameter of about 300 nm and 6 μm in length have been synthesized without any catalyst by nanoparticle assisted laser ablation deposition. The laser action was observed in the nano-rods under an optical excitation at 355 nm, indicating a high quality of the crystal.

Pulsed laser rapid annealing of silicon-germanium (SiGe) films on quartz glass substrate was investigated. Laser-induced melt-regrowth properties were analyzed by the transient conductance measurements. The maximum electrical conductivity of the germanium films associated with the maximum melt depth was increased from 370 to 4420 S/cm as laser energy density increased from 130 to 200 mJ/cm². The complete melting of the films was observed at laser energy density above 200 mJ/cm². The electrical conductivity of the silicon films was increased from 340 to 4480 S/cm as laser energy density increased from 280 to 530 mJ/cm². The melt duration of germanium films slightly increased from 73 to 81 ns as the laser energy density increased from 130 to 180 mJ/cm². On the other hand, the melt duration of the silicon films was increased from 56 to 120 ns as laser energy density increased from 330 to 500 mJ/cm². In the complete melting condition, they were furthermore increased to 117 and 145 ns for germanium and silicon, receptivity. The average size of crystalline grain was increased from 66 to 120 nm as germanium concentration increased from 20 to 60%. The crystallization to the lateral direction induced by the deep melting and rapid solidification increased the grain size.

(103) preferentially oriented ferroelectric SrBi₂Ta₂O₉ (SBT) thin films were sequentially prepared after depositing bismuth (Bi) seeding layers at 600°C on to the (111) oriented Pt/Ti/SiO₂/Si substrates by metal organic chemical vapor deposition (MOCVD). The SBT films with Bi seeding layers showed stronger (103) orientation than those without the Bi seeding layer. Then, the (103) oriented SBT films were irradiated by the excimer laser annealing system (ELA) with line beam (0.4 mm x 200 mm) in order to improve the crystallinity. The surface roughness (Ra) and gradient angle (Δa) of the SBT films irradiated by the excimer laser drastically decreased to Ra = 2.27 nm, Δa = 7.17∠ in comparison with those of as deposited films of Ra = 8.15 nm, Δa = 18.17∠, respectively. The breakdown voltage (abrupt jump of leakage current) with irradiated films was significantly improved to 5 V compared with that of as deposited films of 2V.

For the application of F₂ lasers to micro-/nano-fabrication including photolithography, one of the important research subjects is to eliminate the chromatic aberration, and combination of lenses made of two optical materials with different refractive indices is the effective way. However, only CaF₂ is widely applied to lenses for a vacuum ultraviolet (VUV) beam, and a "second material" to be paired with CaF₂ is strongly requested. Here, we examined two fluoride crystals which are transparent in the VUV region, BaF₂ and LiCaAlF₆ grown by the Czochralski technique, as candidates for VUV optics. We investigated the change of the VUV transmittance and the onset of optical damage of these fluoride crystals against F₂ laser irradiation. These crystals showed good optical tolerance against cumulative F₂ laser irradiation, and the damage threshold of LiCaAlF₆ was similar to that of VUV grade CaF₂ while that of BaF2 was about half of the other two fluoride crystals.

We report on dynamical observation about interaction of the fundamental radiation from a Q-switched Nd:YAG laser to the surface of PMMA observed by an imaging system with nanosecond time resolution, with special emphasis on stress waves inside the sample. We observed stress wave which propagated into the material and a pressure wave propagated into the atmosphere by shadowgraph and photoelastic methods. In the shadowgraph images, a shadow corresponded to the longitudinal elastic wave was clearly observed in the bulk. In photoelasticity images, another contrast which should correspond to the transverse wave was also observed. The contrast of the photoelasticity images depended on laser pulse energy. The contrast and thus the amount of absorbed energy were affected by the surface roughness: roughness greater than 1 micrometer caused complete absorption of laser energy at the surface. Based on this result, we try to examine the effects of incidence angle of the laser to coupling between laser radiations and the material.

A laser spray method, which melts and ablates ultra-fine powder dropped at a small angle to a focused FHG Nd: YAG laser beam in the air, has been developed. The powder contains carbon of 5 μm in diameter and silica of 0.8, 4 and 63 μm in diameter. The 30 μm diameter beam is focused on the substrate in the vicinity of a syringe outlet. The leakage beam falls on the substrate to be deposited and can be expected to perform the effect of annealing. Deposited silica coatings on nickel substrates were analyzed with a scanning electron microscopy, energy dispersive X-ray spectroscopy, and X-ray diffractometer.

A YAG laser of 266 nm is focused just above or at the surface of a Ni substrate in a near critical CO₂ chamber. Since the compressibility of CO₂ becomes very high, strong shock waves may be produced by laser irradiation. We are going to investigate the dependence of the nano structures for nickel and CO₂ on the laser power and the focus point. After the laser radiation, we found fine grains on the Ni substrate with a scanning electron microscopy and energy dispersive X-ray spectroscopy.

The cleaning of photoresist residues on Si and ITO substrate is necessary in electronics device fabrication in order to improve the device performance and manufacturing efficiency. This study is about the laser cleaning of the photoresist residues (AZRFP23OK2) on the substrates being able to substitute conventional photoresist ashing and wet cleaning equipment. The laser cleaning effect of Q-switched Nd:YAG laser at 266 and 532 nm in order to remove the residues on Si and ITO substrate was investigated with regard to laser fluence, shots and wavelength. The cleaning efficiency for the residues on Si substrate was higher than that of ITO at the same laser fluence and shots for both 266 and 532 nm. Much more effective cleaning of the residues on the substrate can be done with flowing assistant inert N₂ gas during the laser cleaning process.

50 nm-amorphous silicon films were crystallized by the pulsed laser-induced electrical-current joule heating method. Holes with diameter of 6 μm were formed within silicon strips, in order to control the position of the formation of crystalline grains. Large crystalline grains of 10 μm were formed between the holes in lateral direction from the observation of the photograph of the optical microscopy. Two dimensional heat flow simulation suggested that a temperature gradient was the ~1 x 10⁵ K/cm.

Fiber lasers have a number of distinct advantages over their more conventional solid state laser alternatives. These advantages include size, reliability, wavelength selectivity, heat dissipation, wall plug efficiency and operational cost. Furthermore they can be operated without the need for active cooling or optical alignment. Consequently the market for these more traditional laser sources are beginning to be eroded by the emergence of fiber lasers. In 1999 high power fiber lasers became a reality, with the world's first single-mode fiber laser exhibiting in excess of 100W cw output. However it was soon recognized that conventional small core, high NA fiber designs were not appropriate to applications requiring further scaling of the output power. More specifically it was found that the maximum achievable output power in such fibers were restricted by a fundamental susceptibility to optical nonlinearities, including stimulated Raman scattering (SRS), stimulated Brillouin scattering (SBS) and self-phase modulation. In order to overcome the limitations imposed by these parasitic nonlinear processes, it has been necessary to develop fibers with high rare-earth dopant concentrations in relatively large core, low numerical aperture fibers. These so-called large mode area (LMA) fibers are directly responsible for the recent explosion in demonstrated diffraction-limited beam quality output powers, now approaching the kW-level from a single fiber. To further scale the output power it is necessary to combine the output of several fiber lasers. Indeed, for a number of industrial and military applications it is desirable to scale the total output power to between several and hundreds of kW's. It is therefore advantageous to be able to coherently combine the beams from multiple fibers and this it turns makes it desirable for the fiber to also be polarization maintaining. This provides yet another layer of complexity to the fiber design but such fibers are now a commercial reality. In this paper we review the recent and ongoing advantages in fiber design that is facilitating the development and production of lasers and amplifiers with ever increasing output powers.

Developers building high-power fiber lasers and diode pumped solid state lasers can receive significant benefits in thermal management and reliability by using single emitter multi-mode diodes in distributed pump architectures. This proposed distributed architecture relies on independent single emitter pump lasers and a modest level of pump redundancy. Driving the remaining diodes slightly harder componensates individual diode failures. A model of the ensemble lifetime based on module failure rates and power-scaling factors demonstrates that the distributed pump architecture requires random failure rates corresponding to better than 200,000h mean time between failure (MTBF), which meets typical industrial requirements. A high power, pigtailed, multi-mode pump module suitable for commercial applications is created through this model. Critical elements are based on telecom architectures, including the optical train and the fiber alignment. The module has a low thermal resistance of 4°C/W from the chip-on-sub-mount to the external heat sink, coupling efficiency of over 80% into 0.2 NA, and demonstrated reliable output power of over 5W cw with peak wavelengths near 915 nm. Individual pump modules are predicted to produce 5W cw output power with an MTBF of more than 400,000h. The relationship between anticipated MTBF requirements, test duration and test population is shown.

Coherent beam combining of many fiber lasers by the Y-shaped complex resonator method realizes both power scaling and spectral narrowing. The basic characteristics of this Y-shaped coherent array, scalability of power summation, and bandwidth narrowing property are presented. As high as 85% addition efficiency with only a few longitudinal-modes was obtained in an array of eight 10-nm bandwidth lasers coupled by fused fiber couplers. By threshold control of the constructive-interference supermodes, high-speed (>1 kHz), high-contrast-ratio (>100) coherent control of beam direction has also been demonstrated. Mass-free and reaction-free properties can realize high-speed laser-beam scanning, which will be quite useful in many applications such as material processing and space communications.

Rare-earth-doped fibers have established themselves as an attractive and pwoer scalable solid-state laser concept. In continuous-wave operation output powers approaching the kW-regime with diffraction-limited beam quality have been demonstrated. In the pulsed regime average powers of more than 50 W even for femtosecond fiber laser systems have been reported. We discuss the feasibility of high average power (> 100 W) and high energy (~100 μJ) femtosecond fiber CPA systems. Novel fiber geometries based on microstructured large-core air-clad fibers are introduced, which allow for a significant performance scaling. Furthermore, an all-fiber CPA system including an air-core photonic band-gap fiber compressor is presented. This approach opens the avenue to a completely fiber integrated high performance short pulse laser system. Applying the ultrafast fiber laser system three-dimensional photonic structures in different glasses and also crystalline media have been generated by tight focusing of the ultrashort laser pulses into the material. Using the ultrashort pulse lasers we fabricated low loss waveguides (< 0.5 dB/cm) at writing speeds of 100 mm/s. The influence of the writing speed on the produced structures as well as their optical properties will be discussed in detail.

The trend in micro-machining lasers is toward greater average power and higher repetition rate, in order to increase throughput, with pulse energy and peak power held roughly constant, as determined by the small scale of the feature. At repetition rates beyond 500 kHz, conventional high-power Q-switched Nd lasers will reach fundamental limits. We demonstrated a fiber-based oscillator-amplifier architecture which produces pulse repetition rates in the 0.5 - 5 MHz range and pulse durations in the 0.5 - 1.5 nsec range. The oscillator is a compact (35 cm³ package) passively Q-switched Nd:YVO₄ laser oscillating at a single frequency. By amplifying this laser in fiber, we demonstrated 10-W average power at the two wavelengths of 914 nm and 1064 nm. At 1064-nm, Yb-doped large mode area fiber will allow scaling of average power to over 100 Watts, with peak power of tens of kW, in a diffraction-limited beam. Excellent conversion will be possible to visible and UV using the robust nonlinear material LBO. By opening up a new range of repetition rates and pulse lengths, at IR, visible and UV wavelengths, in a high power design that has the packaging and efficiency advantages of fiber, new micro-machining applications may be enabled.

It is reported on micro-machining using as a laser source, a high peak power fiber pulse laser, MITSUBISHI CABLE'S LP155R that consists of a two stage erbium doped fiber amplifier (EDFA) designed specialty for pulse amplification. The output of the fiber laser is a transversal single mode and its wavelength is 1.55 μm. The peak power and the pulse width of FWHM in our catalogued products are 10 kW and 2 ns respectively. A laser source having preliminary specification of 2 kW and 80 ps is also used. The high peak power and short pulse created in these systems make precise micro-machining possible with little thermal damages around the processed regions. It is demonstrated that microdrilling and microscribing of metals and crystals such as tungsten, diamond-like-carbon (DLC) coating, stainless steel 304, silicon, sapphire and lithium-niobate. The microstructures of the processed specimens observed by a scanning electron microscope and an optical microscope are also introduced in this paper.

High power single-mode fiber-lasers with CW output power 40 - 200 W was applied to microwelding. Thermal conduction equations of a square heat source were derived to calculate the temperature distribution and the mean temperature within the beam area. The penetration depth can be predicted assuming the beam-irradiation area is heated up to the boiling temperature of the material. High-speed photographs showed that a keyhole with the size of approximately focused beam spot is formed in the molten pool, of which diameter is in good agreement with the measured spot size. The humping defect can be suppressed by using fine beam spot size, because the width of the flow channel beside the keyhole is kept widely even at very high welding speeds rsulting in stable flow of the molten metal. Ultra-high speed welding up to a velocity of 1500 mm/s was attained without humping in SUS304 stainless steel foil. Sound lap welding of thin foils of 10 μm to 30 μm is demonstrated at welding speed of 920 mm/s. Penetration welding of 800 μm in thickness was achieved at laser power of 200 W.

The combination of a gray tone phase mask with a laser assisted wet etching process was applied to fabricate complex microstructures in UV transparent dielectric materials. This one-step method allows the generation of arrays of plano-convex and Fresnel micro-lenses using a conventional XeCl excimer laser and an absorbing liquid, which is in contact with the UV transparent material. An array of plano-convex micro-lenses was tested as beam homogenizer for a high power XeCl excimer and ps Nd:YAG laser. The roughness of the etched features varies from several μm to 10 nm, depending on the laser fluence and concentration of the dye in the organic liquid. The etching process can be divided into several etching mechanisms which vary with laser fluence.

Laser-induced plasma-assisted ablation (LIPAA) process developed for glass materials has been applied for micromachining of a variety of transparent hard and soft materials. We have developed the proto-type LIPAA system using a second harmonic of diode pumped Q-switched Nd:YAG laser for the practical use. In this paper, micromachining and scribing of glass and sapphire is demonstrated using the developed system. Additionally, another application such as selective metallization of glass and polyimide with successive metal plating process is investigated. However, mechanism of this process is complex and still remains unknown. To have a better understanding of this process, double-pulse irradiation of a near-IR femtosecond (fs) laser with a delay time is also investigated. A possible mechanism is discussed based on the obtained results.

A novel direct-write glass metallization based on laser induced plasma assisted ablation (LIPAA) was investigated. Laser is passed through a glass substrate and irradiated onto a metal target placed beneath the substrate. By tuning laser fluence above target ablation threshold, target ablation and plasma generation occur. The plasma flies towards the glass at a high speed and deposits metal materials onto glass backside surface. Metal films were fabricated and their sheet resistances were measured by a four-point probe. It was found that sheet resistances of the metal films vary with processing parameters. Experimental results reveal that low resistivity metal film (< 0.3 Ω/∠) can be obtained at an optimal laser scanning speed and pulse repetition rate. When target-to-substrate distance increases, film resistance also increases. Optimal design of overlap schemes among metal tracks provides a lower film resistance. Meanwhile, thin film and bulk metal targets were used to study their difference on film resistance. It was discovered that deposition using thin film target is more efficient. Laser annealing technique was also applied to activate the deposited metal materials to get higher quality glass surface metallization.

In this study, three-dimensional microstructures are manufactured using a laser micro machining system, which consists of an ultraviolet pulsed laser and a stage having five degree of freedom. The works are controlled to move by the five-axis micro machining system to an arbitrary position, and three-dimensional microstructures can be manufactured. We have succeeded in machining a micro gear, a micro windmill and a micro globe made of polyamide resin by this system. We were machined a conic shape to study a precision limit of this system. We have succeeded in machining a conic tip having radius of curvature less than 1 μm by use of this system. In order to try improving the laser machining characteristics, we have modified the optical system in order to irradiated materials with fourth harmonics and fundamentals of an Nd-YAG laser, simultaneously. We had observed decrease of debris by simultaneous irradiation of the UV-laser and the IR-laser.

We have developed a novel process for releasing MEMS and nano-scale devices formed in SiO₂ on a Si substrate. Current approaches for releasing MEMS made of SiO₂ use wet chemical etches (e.g. EDTA or KOH) or gas phase chemical etches such as xenon difluoride. These approaches are inherently messy and difficult to control. We have shown that it is possible to release patterned SiO₂ structures using a direct write laser assisted chemical etching technique. The developed process removes Si only from the immediate area leaving behind the SiO₂ device. The technique allows the surrounding larger area of the Si wafer to be conserved for use in packaging or integration with electronics. Further, as the release is accomplished in the gas phase, we see none of the problems of "stiction" associated with a liquid etch release process. In fact, we have found this method to be so gentle that we have been able to release devices made from SiO₂ films on the order of hundreds of nanometers.

Micro-conductive patterns formed by selective electroless Ni-B plating process were fabricated to investigate the various distribution of the seed layer on insulating substrates. Selective distribution of the seed layer was forming through successive steps of laser ablation, activation treatment, mechanical polishing. A KrF Excimer laser (wavelength of 248 nm) ablation was carried out on the PMMA (Polymethymethacrylate), PET (Polyethylene Terephalate), PC (Polycarbonate) and PI (Polyimide substrates. The UV-vis spectrometer analysis showed that PMMA was a weaker absorber than other polymers at the wavelength of 248 nm. The geometrical shape of structure formed is affected by absorption coefficient. Surface morphology and characteristics after laser ablation and electroless plating is observed by Field Emission Scanning Electro Microscope (FE-SEM). As a increasing the depth of substrate patterned by laser ablation, plating was precise. Finally, we concluded this method to be suited for manufacturing micro-conductive patterns on insulating substrates without lithography.

The development of micro power systems, on the mm size scale, is necessary for emerging technologies in small, portable micro-electronic device applications. Direct-write processes are used to produce the high-power, low-power and recharging elements of such mesoscale micro power systems. Successful fabrication of alkaline and lithium based micro-batteries, micro-ultracapacitors, and dye-sensitized micro-solar cells are possible on various low processing temperature and flexible substrates using laser direct-write approaches that are ideally suited for the many different structurally complex electrochemical materials used in these systems. Increased areal energy density is realized by depositing thick layers > 10 μm, while maintaining patterns as small as 2 mm². Micro-ultracapacitors exhibit high power densities > 250 mW/cm², while primary alkaline microbatteries exhibit open circuit potentials of 1.5 V with high capacities and discharge currents up to 1 mA. Secondary LiCoO₂ and LiMn₂O₄ based microbatteries employing a novel nanocomposite solid-state electrolyte exhibit open circuit potentials > 4 V and have shown multiple recharging cycles without loss of capacity. Results of the different systems will be discussed with particular emphasis on the combination of elements to produce hybrid micro power systems.

Significant reduction in weight and volume for a given circuit design can be obtained by embedding the required surface mount devices, bare die and power source elements into the circuit board. In addition, embedded structures allow for improved electrical performance and enhanced function integration within traditional circuit board substrates and non-traditional surfaces such as the external case. Laser-based direct-write techniques can be used for developing such embedded structures at a fraction of the cost and in less time that it would take to develop system-on-chip alternatives such as ASIC's. Laser micromachining has been used in the past to machine vias and trenches on circuit board substrates with great precision, while laser forward transfer has been used to deposit patterns and multilayers of various electronic materials. This paper describes recent work performed at the Naval Research Laboratory using the above laser direct-write techniques to machine the surface and deposit the materials required to embed, connect and encapsulate individual electronic components and microbatteries inside a plastic substrate.

Micro ceramic parts are used in electronics, medicine and MEMS for different purposes such as isolators, rigid supports and biocompatible components. Furthermore ceramics are increasingly used as a tool material since high hardness combined with inert surface properties against lubricants qualify them for micro stamping and forming tools. Especially polycrystalline diamonds have a growing market in micro stamping and forming applications with tool geometries < 100 μm and accuracies < 10 μm at surface qualities < 2 μm. Mostly ceramics are processed by high precision grinding but for 3-dimensional parts grinding processes do not offer the possibilities for small and complex geometries. Here laser ablation offers new possibilities by selective processing of all kind of technical ceramics. Using frequency tripled Nd:YAG-Lasers at wavelength of λ = 355 nm structures with single size geometries less than 10 μm can be produced. For the manufacturing of 3-D-parts and processing of micro structures on larger 3D-Parts a multi-axes machine with 5 moving axes for the parts and additionally 2 scanning axes for fast laser movements have been set up. With this system different ceramic parts have been processed using a 5W frequency tripled high repetition rate Nd:YAG-Laser. Optimum accuracies and surface qualities have been achieved using scanning strategies with varying scanning angles for subsequent ablation layers, a combination of contour mode and form filling scanning ablation. For a further increase of surface qualities in terms of roughness a combination of ablation and polishing using different laser parameters has been used leading to surface roughness < 0,5 μm at polycrystalline diamond.

Plastic material can be also bent by laser forming in the same way as metal material, and larger bending angle can be obtained as compared to metal material. However, its deformatio nmechanism has not been yet clarified. Therefore, in this study, the machining characteristics and the deformation mechanism of plastic in YAG laser forming were made clear by experimental and numerical analysis. Small temperature gradient was obtained by thermal analysis in laser forming of high density polyethylene. The plastic material could be bent due to high viscoelasticity in spite of small temperature gradient. Specimen was first bent by the temperature gradient in thickness direction in a few seconds after the laser irradiation. Then, the temperature of specimen became almost the same in thickness direction, and the temperature gradient appeared only in side direction. Therefore, the deformation of specimen was occurred by the contraction of specimen in side direction and the effect of initial shape, which was deformed by the temperature gradient just after the laser irradiation. Besides, it was clarified that small thermal conductivity of plastic material lead to low cooling speed. Therefore, sufficient cooling time is necessary in order to control the deformation accurately, since the temperature of specimen should be kept equal before every laser irradiation.

Biomolecule microarrays are a kind of biosensors that consist in patterns of different biological molecules immobilized on a solid substrate and capable to bind specifically to their complementary targets. In particular, DNA and protein microarrays have been revealed to be very efficient devices for genen and protein identification, what has converted them in powerful tools for many applications, like clinical diagnose, drug discovery analysis, genomics and proteomics. The production of these devices requires the manipulation of tiny amounts of a liquid solution containing biomolecules without damaging them. In this work laser induced forward transfer (LIFT) has been used for spotting a biomolecule in order to check the viability of this technique for the production of microarrays. A pulsed Nd:YAG laser beam (355 nm wavelength) has been used to transfer droplets of a biomolecule containing solution onto a solid slide. Optical microscopy of the transferred material has been carried out to investigate the morphological characteristics of the droplets obtained under different irradiation conditions. Afterwards, a DNA microarray has been spotted. The viability of the transference has been tested by checking the biological activity of the biomolecule in front of its specific complementary target. This has revealed that, indeed, the LIFT technique is adequate for the production of DNA microarrays.

Due to special material properties, among others their two-way memory effect (TWME), shape memory alloys (SMA) are finding increasing attention in micro system technology. However, only slow and quite complicated training methods are available to induce the TWME. At the Laser Zentrum Hannover e.V., investigations are being carried out to realize the induction of the TWME into SMA components using laser radiation. By precisely heating SMA components with laser radiation, local tensions remain near the component surface. Concerning the shape memory effect (SME), these tensions can be used to make the components execute complicated movements. Compared to conventional training methods to induce the TWME, this procedure is faster and easier. Further, higher numbers of thermal cycling are expected because of the low dislocation density in the main part of the component. Results regarding the dependence of the laser induced TWME on material and machining parameters will be presented.

Ultrafast lasers have become reliable tools for material processing on reduced scales, with extended options for process control and optimization. The additional possibility to shape the temporal envelope of ultrashort laser pulses by Fourier synthesis of spectral components enables completely new opportunities for optimal processing of materials. The concept of optimizing laser interactions is based on the possibility to regulate the energy delivery rate and to achieve control of laser-induced phenomena. An experimental demonstration of the technique showing the possibility to design excitation sequences tailored with respect to the material response will be described, laying the groundwork for adaptive optimization in materials structuring. We present recent results related to the implementation of self-learning loops based on temporal shaping of the ultrafast laser pulses to control laser-induced phenomena for practical applications. Besides the fundamental interest, it will be shown that under particular excitation conditions involving modulated excitation, the energy flow can be controlled and the material response can be guided to improve processing results. Examples will be given illuminating the possibility to optimize the kinetic properties of ions emitted from laser-irradiated semiconductor samples, uisng excitation sequences synchronized with the phase-transformation characteristic times, unfolding also interesting perspectives for "intelligent" processing of materials.

In this article, a plasma model with quantum treatments is proposed to predict ablation threshold, depth, and crater shape in femtosecond laser ablation of glasses at peak intensities on the order of 10¹³ ~ 10¹⁴ W/cm². Impact ionization and photoionization are the two major competing mechanisms considered for plasma generation using the flux-doubling model. Using a modified free electron plasma model, the proposed model considers the time and space dependent optical properties of ionized glass. The quantum treatment based on the Fermi-Dirac distribution is employed to investigate the free electron heating. The free electron relaxation time is calculated by using a quantum model derived from the Boltzmann transport equation. The predicted threshold fluence and ablation depth for barium aluminum borosilicate and fused silica are in excellent agreement with published experimental data. The model greatly improves the prediction precision of ablation depth and can predict the crater shape in femtosecond ablation of glasses. Some interesting phenomena observed experimentally, such as the bottom of the ablation crater by a femtosecond Gaussian beam could be rather flat under special ablation conditions, are well explained by the proposed model.

Single pulse drilling and percussion drilling of micro holes (diameter 100 μm, depth 2 mm) with Nd:YAG laser radiation (pulse duration 100 - 500 μs) in stainless steel (X5CrNi18-10) and nickel-based superalloy (CMSX-4) are reported. The development of the hole geometry, especially the hole diameter depending on the focal diameter including caustics and the thickness of the melt at the hole wall, is investigated. The experimental results are compared to the calculations of a physical model describing the motion of the melt front, the phase boundary between liquid and solid. Closures resulting from melt in the hole are detected by recording the expansion of plasma using high speed photography (50000 fps). The quality of drilled holes, e.g. conicity, thickness of recast and closures, is investigated by metallography and optical microscopy. Timescales of physical processes as the onset of melting and vaporization, the time to stationary melt flow and geometrical scales like the hole depth, the closure depth and the hole diameter are determined experimentally and numerically.

In this Paper, laser cutting of super abrasive thin stick stone (SATSS) whose grains are CBN and diamond using Nd:YAG laser is studied. We have investigated cutting characteristics of SATSS and strength of the heat affected zone (HAZ) on the surface cut with laser. As a result, SATSS of 3 mm in thickness can be cut off with the width of 0.2 mm in maximum, and there is no chipping at the edge of the surface cut with laser. In the case of CBN stick stone, cutting time with laser is 2.5 times faster than that with diamond blade, and 15 times faster in the case of diamond one. There is a HAZ with a thickness of 0.05 mm. In this HAZ, the abrasive grains are oxidized and their crystal structures are changed by the heat of laser irradiation. However, laser is absorbed effectively by the HAZ, and the HAZ raises the strength of SATSS because the pores inside of the HAZ are closed by the re-solidified vitrified bond. From these results, it is shown that laser cutting can apply to the manufacturing of the SATSS and improve the productivity and the quality.

In order to achieve high packaging density and high performance of LSI assembly, 3D stacking approach of electronic and opto-electronic devices has been considered where chip to chip interconnections are realized via micro through-holes formed by rapid excimer laser drilling. Since local damages due to temperature increase and thermal stress might cause device degradation, it is crucial for the process optimization to evaluate the quantity of thermal and stress fields around holes. In this study, we conducted transient thermo-mechanical finite element analysis for laser drilling of GaAs and Si chips considering temperature dependence of materials properties. Relationship among laser fluence, pulse width, repetition times, and the temperature increase and thermal stress are thoroughly investigated using 2-dimensional axisymmetric models.

Laser milling of diverse materials has been demonstrated with short pulse lasers ranging from microsecond to femtosecond pulse durations, and with wavelengths from the far infrared to vacuum ultra-violet. In all cases a balance between quality, throughput and cost of ownership must be struck in order to determine commercial relevance. Latest generation Q-switched Diode Pumped Solid State Lasers offer the potential to enable the industrial uptake of laser milling for a wide variety of materials including aerospace alloys, thermal barrier coatings, tool steels, diamond and diamond substitutes. This paper will investigate these practical applications of laser milling with reference to comparative laser and non-laser processes.

Compact short pulse (200 - 350 ps) laser systems using SBS and SRS pulse compression techniques have been constructed. Fine processing of aluminum nitride and silicon wafer has been studied by using these laser pulses and compared with the results processed by 60 femto second laser system. Through-holes are formed on wafers by irradiation of the laser pulses, and the relationship between hole shapes and the processing conditions has been studied. The hole shape relates with the focusing length of the lens, laser fluence, pulse width and the wave length. Trepanning technique has been examined also to improve the hole shape. The result is quite.

Stereolithography is a technology which converts 3-D CAD data to three-dimensional plastic models as a 3-D printer does. The shaped plastic model is useful for a verification model, an engineering design model, a working model, a master model for vacuum casting, a medical simulation model and etc. The fundamental technology of the stereolithography consists of four elements; hardware, software, photo-curable resin and know-how to use, whereas they are based on the key technologies for fabricating model. Out of these photo-curable resin has become the most important item, because the customer uses shaped plastic models with the resin for the research and development.

Stereolithography is one of the Rapid Prototyping and manufacturing technologies which enable to fabricate three dimensional structures easily, quickly and automatically from computer-aided design (CAD) drawing. But it is much difficult to realize microfabrication quickly and accurately using conventional laser-scanning stereolithography due to thick layer of lamination and long time of fabrication. In order to overcome these difficulties, the liquid crystal display (LCD) microstereolthography has been developed in our laboratory, which enable microfabrication of a complete layer by only one irradiation, at high speed as well as high accuracy by continuous laminating of thin layers using the LCD as a live-motion mask. We performed the fundamental experiments to fabricate general 3D micro structure consisting of the overhanging shape using the LCD live-motion mask microstereolithography, and tried to fabricate a microspring with several ten micrometers size as one example.

Ongoing progress in material research and processing industry is fueled to a large extent by the technique of pulsed laser deposition (PLD). With this powerful and versatile deposition method, multi-component target materials can be ablated and deposited onto a substrate to form functional layers with tailored physical properties. Monitoring of growth parameters such as thickness and surface roughness is mostly performed in-situ via electron diffraction or other diagnostic tools. High pulse energy excimer lasers with photon energies as high as 7.9 eV lend maximum flexibility to the technique of pulsed laser deposition since virtually every target material is amenable to excimer laser ablation and its subsequent stoichiometric transfer to a substrat. Spectral properties as well as recent technical advances in excimer lasers for thin film applications are shown in this paper.

Ti:Sapphire lasers remain the most widely used utlrafast laser. However, precise optical alignment and environmental control are necessary for continuous, long-term stable operatoin of the laser. IMRA's FCPA laser is an air-cooled, Yb fiber-based ultrafast laser designed to operate in an industrial environment and provide a stable, high-quality laser beam. In this work, the micromachining performance of the FCPA laser is directly compared with a conventional Ti:Sapphire regenerative amplifier laser. An experimental study was conducted to determine the ablation threshold and etch rate for a variety of materials (including metals, semiconductors, and dielectrics). The materials chosen for the experiments cover a wide range of optical, mechanical and physical properties. Similar focusing conditions were used for both lasers in order to ensure that any differences in the results are primarily due to the different characteristics of each laser. For materials with a relatively low ablation threshold, the full energy of the Ti:Sapphire laser is not needed. Furthermore, it is near the ablation threshold where ultrafast laser processing provides the benefit of minimal thermal damage to the surrounding material. Although the relatively low pulse energy of the FCPA limits its ability to ablate some harder materials, its high repetition rate increases the material processing speed and its good beam quality and stability facilitates tight, efficient focusing for precise machining of small features.

At laser intensities near the threshold fluence, the electron temperatures in metals heated by an ultrashort pulse can be comparable to the Fermi temperature. As the existing approximations for material properties used in the two-temperature models are limited to electron temperatures that are much lower than the Fermi temperature, the models are suitable only for low fluences. This paper extends the existing estimations for optical and thermal properties to high electron temperatures by the following improvements: (1) using the Fermi-Dirac distribution, the heat capacity of metal free electrons is calculated; (2) the free electron relaxation time and electron coductivity are determined by using a quantum model derived from the Boltzmann transportation equation for dense plasma; and (3) the free electron heating and interband transition are both taken into account using a modified Drude model with quantum adjustments to calculate the reflectivity and the absorption coefficient. The proposed two-temperature model is employed to calculate the heating process of thin metal films until melting occurs, which is assumed to be the initiation of damage. The predicted damage threshold fluences for 200 nm gold film using the proposed model are in good agreement with published experimental data. The damage threshold fluence as a function of pulse duration is also studied.

Femtosecond laser pulses successfully ablated the work hardening layers on SUS316L used in boiling water reactors. The measurement of hardness inside the material clarified this new technique to reduce the risk of Stress Corrosion Cracking.

The quenching of the ε phase of iron, which has not been observed under a conventional shock compression, was attained using a femtosecond laser. The crystalline structure in a recovered iron sample was determined using an electron backscatter diffraction pattern, an electron diffraction pattern, and a synchrotron X-ray diffraction methods. A small quantity of the γ phase of iron also existed. Thermodynamic state inside the shock front has to be known because the shock induced phase transition occurs inside the shock front. Therefore, the temperature inside the shock front was calculated using thermodynamic equations. It was found that the ε phase was induced by the shock itself but not the γ phase. The γ phase was suggested to be induced as an intermediate structure between the α-ε transition. The femtosecond laser driven shock may have the potential to quench high-pressure phases which has not been attained using conventional methods.

The study of the effect of nanosecond and femtosecond pulse duration of laser processing of a biodegradable poly(ε-caprolactone) (PCL) film was carried out. PCL has a melting temperature of 60°C and shows symptom of melting when processed with lasers. A very high energy and localized source of laser irradiation is required for effective material removal without melting. Nd:YAG laser with wavelength 355 nm and pulse duration of 7 ns and Ti:Sapphire femtosecond laser with wavelength 800 nm and pulse duration of 110 fs were used. The use of the femtosecond laser produced neat drilled-through holes with excellent repeatability while the Nd:YAG laser performed with fairly good repeatability due to symptoms of melt and occasional tearing of film as a result. The ablated surface of the film was studied and the morphological features were analyzed using phase contrast optical microscopy and scanning electron microscopy (SEM). The present study demonstrated that laser ablation using nanosecond and femtosecond pulse duration are able to achieve good micro-drilling on the PCL with high degree of success and precision. This paved the way for enhancement in membrane tissue engineering.

The experimental results of wide band-gap materials treatment by femtosecond laser pulses are presented and discussed. Borosilicate glass drilling in air and vacuum, the surface and in-bulk three-dimensional laser processing with sub-micrometer resolution are subject of investigatios. Technical issues relevant for achieving high spatial resolution in order to meet requirements of nanotechnology at feature size smaller than 10 nm along with the issues of fabrication efficiency are outlined. Also, we show a concept of modular laser processing system, which can be flexibly optimized for processing by femtosecond laser pulses.

Precision micro holes and structures with smooth internal surfaces are introduced. We adopted a high repetition rate femtosecond laser to form optically damaged structures inside a silica glass. The glass is dissolved by HF aqueous solution after the laser irradiation. Through this process, we could obtain micro structures with smooth internal surfaces. We investigated the effects of laser repetition rate on surface roughness. It is suggested that one of the causes increased hole surface roughness is the increase in the defects by the laser irradiation.

Processing of a human fingernail surface by a tightly focused femtosecond laser pulse is investigated. The processed structure in the fingernail surface is strongly dependent on focus position and irradiation energy of a laser pulse. A variety of structures depending on the focus position were observed. A sudden change in the size of the processed structure according to the irradiation pulse energy is also observed. From a linear theoretical estimation based on the diffraction of a laser beam, we found that the sudden change is mainly due to the diffraction pattern generated by the circular aperture of an objective lens. The processing feature is investigated by comparing the structures processed in a fingernail with those processed in glass.

The design, fabrication and evaluation of photonic crystals (PhC) have attached more and more interests in recent decades. In this paper, a homemade femtosecond laser microfabrication system is described. The optimization of working parameters, especially for resolution power or 2-photon microfabrication and the spatial overlap ratio of scanning, is presented. After that, several log-pile type PhCs are made through 2-photon induced photopolymerization. And their reflection spectrums are got with an infrared spectrometer equipped with an infrared microscope. For comparison, simulation result of photonic bandgap (PBG) using a plane-wave based transfer-matrix method is shown. The measured reflection spectrum of our PhC is agreed with the simulation one quite well.

Results of microdrilling and cutting in silicon and glass with picosecond lasers are presented. Recent progress in the development of diode-pumped mode-locked (picosecond) lasers has increased interest in their industrial application, especially in microfabrication. Our experiments started from single-shot patterning and extended to cutting and drilling of complex shapes. They are directed at finding the right niche for these lasers. All-solid-state Nd-doped lasers of PL2200 series with high peak power were used. Pulse duration of 60 ps and pulse energy up to several mJ at 1 kHz repetition rate allowed to cover a wide energy density range above ablation threshold for processing. Limitations of processing windows for laser fabrication with picosecond pulses were established. The results are a consistent step in search of optimal regimes for crack-free processing with minimal deposit of material and high quality of ablated surface.

A shape of a structural change inside human fingernail produced by a focused femtosecond laser pulse drastically changes depending on the irradiated pulse energy. The structural changes are observed as a dark region by a microscope with transmitted illumination. When the energy is close to the threshold for producing the structural change, it had a linear shape, and at higher energy, it had conical shape. We observed a phenomenon of increase of fluorescence intensity at the structural changes. The fluorescence intensity is higher than its surrounding auto-fluorescence of a fingernail. The spectrum of the increased fluorescence coincided with the auto-fluorescence spectra of a fingernail and a pure keratin. The increase of fluorescence intensity was also observed with the fingernail heated by a drying oven. It is suggested that the fluorescence increase of the structural change is most likely caused by locally heating caused by femtosecond laser pulse irradiation. We demonstrate the fluorescence increase of the structure is useful to read out three-dimensionally recorded data inside human fingernail. Furthermore, we demonstrate the fluorescence can be observed over a half year.

At the bottom of ablation craters produced in many materials, e.g. dielectric and silicon crystals, by the impact of femtosecond laser radiation, regular periodic structures are observed with a feature size at the order of a few 100 nanometers, much smaller than the incident wavelength. Their orientation depends strongly on the laser polarization but not on any intrinsic crystalline parameters. An increasing number of shots results in higher contrast, better developed structures, indicating a positive feedback. The region around the impact is shown, by micro Raman spectroscopy, to undergo phase transformations like under high pressure. The structure spacing appears to depend crucially on the depth of the perturbed volume, i.e. the incident (and absorbed) energy. All observations suggest that the structures form by self-organization from instabilities induced in the material by the laser input. A general picture suggests that the irradiation results in a rapid, non-equilibrium destabilization of the crystal structure, which should not be confused with melting as a classical thermodynamic process (i.e. temperatures defined as equilibrium properties). Relaxation from this instability results in the self-assembly of the observed structures. Theoretical simulations demonstrate the feasibility of this model, which also is corroborated by comparison to other unstable situations.

Micro- and nanostructuring are very important for the fabrication of new materials and multifunctional devices. Existing photo-lithographic technologies can only be applied to a limited number of materials and used on plane surfaces. Whereas, microstructuring with femtosecond laser pulses has established itself as an excellent and universal tool for micro-processing, it is still unclear what are the limits of this technology. It is of great interest to use this technique also for nanostructuring. With tightly focused femtosecond laser pulses one can produce sub-micrometer holes and structures whose quality depends on the material. We present new results on nanostructuring of different materials with femtosecond laser pulses in an attempt to make this an universal technology, and discuss its reproducibility, and further prospects for quality control.

Nano-sized materials such as nanobump, nanomesh, nanobelt were generated by thin film processing using interfering femtosecond laser beams. To split and interfere femtosecond laser, a demagnification system, with a cylindrical lens in some case, was used. With four interfering femtosecond laser beams, a nanobump array was generated from a gold thin film in a single shot. It became larger and a bead was formed at a top of a bump as the fs laser fluence increased. Moreover, with three or two interfering femtosecond laser beams, ellipsoidal or linear nanobump array was generated. As an application of nanobump array, field emission from a nanobump array was demonstrated for the first time. On the other hand, with higher fluence and four beams, nanohole array was generated, and nanomesh was also generated from nanohole array by scratching. Grating was also generated with two beams, and nanobelt was generated from grating by scratching. Bimetallic nanobelt was generated from multi-layered thin film.

Surface modification of thin diamond-like carbon (DLC) films deposited on stainless steel has been studied by irradiating linearly and circularly polarized femtosecond (fs), 800- and 267-nm Ti:sapphire laser pulses at laser fluence around the ablation threshold. The morphology of the DLC surfaces was observed and characterized with a field-emission scanning electron microscope and a scanning probe microscope. The linearly polarized light produced arrays of fine slender granular structure on the ablated surface, while the circularly polarized light formed a fine dot-like periodic structure. The mean spacing of these fine structures was 1/10 - 1/5 of the laser wavelength used. With an increase in the laser fluence, the size of structure was observed to increase, while the surface roughness decreased. We have analyzed the modified DLC surfaces by observing Raman spectra and found that the nanoscale modification of the DLC films is accompanied with a structural change into glassy carbon. This structural change depended on the fs laser fluence and little on the laser polarization and wavelength.

Microspike-arrays were fabricated by irradiating a femtosecond laser on a tungsten surface through a mask opening in air. Natural logarithm of the calculated intensity distributions diffracted at the edge of the mask opening was qualitatively consistent with the experimental results of the shape and arrays of microspikes fabricated. The shape and the array of microspikes depend on the intensity distribution diffracted at the edge of the mask opening. This microspike-array has a potential to be micro emitter tips.

Beneath lithography, etching and coating, laser technology is necessary to support the production of innovative devices in MEMS, electronic and optical industry. Laser beam sources emitting pulses with durations in the regime between nano- and femtoseconds are winning more and more importance for processing metal, semiconductor and optical materials. Finest structures, cuts and drilings can be manufactured in a high variety of materials like silicon, glasses but also in composite materials like polymers. In this paper a survey on a number of laser based processes for precision manufacturing is presented. With regard to this context, effects and material interactions are discussed and attached to different laser beam sources. The quality of processes as well as their economical meaning from perspective of laser technology is evaluated. An overview about machining and actual trends for ns-, upcoming ps- and fs-laser technology is presented.

The development of the recent years led to an increased importance of frequency-converted diode-pumped solid-state lasers (DPSSL) for industrial drilling, cutting and structuring applications. The UV laser systems show favorable beam absorption in a broad range of MEMS and MOEMS relevant materials like ceramics, metals and polymers. Their short pulses in the range of t_H = 20 nanoseconds and the excellent beam quality offer the possibility of manufacturing with a minimum heat affected zone (HAZ) in the surrounding material and thereby a decreasing of initial fusing and debris. To obtain the reachable ablation quality, especially on metals, in this paper copper, tungsten, tantalum, molybdenum, nickel, iron, aluminum and titanium were machined under identical conditions. Material properties like heat conductivity, optical and thermal penetration depth, are decisive for the magnitude of the mentioned side-effects. The correlation of these physical values of different metals to those effects is the subject of this paper. Results of systematically accomplished experiences using a frequency tripled DPSSL with a wavelength of λ = 355 nm in order to investigate this correlation are presented. Due to thermal effects, the ablation quality of metals differ from each other extremely. These information enable a prediction of the reachable quality of the desired structure.

Machining of metals and other materials is presented using subpicosecond laser pulses at a wavelength of 248 nm. Aiming at high speed sub-μm patterning of large areas, a combination of mask projection and multiple beam interference techniques are employed. A special interference scheme is discussed that enables phase controlled multiple beam interference and allows the flexible fabrication of a vast variety of complex periodic surface patterns. In combination with a special short-pulse beam homogenization technique, two-dimensional periodic surface structures with feature sizes below 100 nm and excellent quality and reproducibility can be fabricated. The UV laser system used for irradiation is a Ti:Sapphire-Excimer hybrid device generating 30 mJ, 300 fs pulses at 248 nm. The high pulse energy and a flat-top beam profile allow a relatively large irradiation spot size. Operating the system at 300 Hz enables high speed patterning of extended surface areas with sub-μm feature sizes.