The range and maturity of commercially useful laser applications are illustrated by selected examples. Macroscopic applications (commercialized or potentially so in the near future) include cutting, machining and welding metals, cutting fabrics, shock hardening of steels, nitrogenization of iron, and laser drilling through rock. Microscopic applications include drilling micro-holes for cooling of jet engine turbine blades, thin film growth, precision machining of structures inside transparent materials and inertially-confined deuterium-tritium fusion. To be commercially useful, these applications take advantage of the special properties of laser light, such as monochromaticity, high brightness, high pulse energy or intensity, wavelength range from soft xray to far infrared and pulse duration from femtoseconds to CW. This talk will be divided into three sections: (a) summary of the theory of laser-materials interactions with examples from published laser impulse production studies, (b) macroscopic applications, (c) microscopic applications and (d) exotic and futuristic applications, including a diode-laser-driven μN thruster for micro- and nano-satellites, and proposals to use lasers to clean hundreds of thousands of small but hazardous space debris from near-Earth space and to launch 5kg payloads into near-Earth orbit.

Japan is one of the most advanced countries in manufacturing technology, and lasers have been playing an important role for advancement of manufacturing technology in a variety of industrial fields. Contribution of laser materials processing to Japanese industry is significant for both macroprocessing and microprocessing. The present paper describes recent trend and topics of industrial applications in terms of the hardware and the software to show how Japanese industry challenges to advanced materials processing using lasers, and national products related to laser materials processing are also briefly introduced.

Micro patterns of some μm size were fabricated by transferring metal thin films using Laser-Induced Forward Transfer (LIFT) technique. The oxygen composition ratio of deposited patterns fabricated by varying laser irradiation conditions was measured by using XPS. Then we investigated the dependence of the oxygen composition ratio of deposited patterns on the thin film-acceptor substrate distance and laser fluence. LIFT was performed using a single shot of KrF excimer laser (wavelength: 248nm, pulse width: 30ns). Sn thin film, with a few hundreds of nanometer thickness deposited on quartz substrate using electron beam evaporation method, were removed by laser irradiation, and deposited on acceptor substrate (Si wafer) after transfer in air under room temperature. As a result of XPS analysis of deposited patterns, it was revealed that the oxygen composition ratio depended on laser fluence and the distance from a thin film to an acceptor substrate and tended to increase and then fall with increase of laser fluence when the film-acceptor substrate distance was fixed. In order to investigate this tendency, we photographed the shadowgraph of the transferring thin film. From this investigation, it was revealed that higher fluence causes higher velocity. As the velocity becomes higher, the time from the beginning of removal to attachment on the acceptor substrate becomes shorter. So the higher laser fluence is, the lower the oxygen composition ratio is.

For the increasing demand of miniaturizing electro-optical devices, Molded Interconnect Device (MID) technology has been taken interest in recent year. MID is a three-dimensional molded component on which electronic circuitry is directly fabricated. The laser structuring process on MID includes the process of forming a copper thin film on a molded component and directly removing only the contour of the circuit using a laser beam. Forming a uniform copper thin film, the laser beam diameter can be made small enough to produce fine patterns with a 50/50 micrometers track/gap combination. This method also simplifies the process by eliminating the need for the photo-resist and mask required in conventional photo imaging processes. The combination of laser wavelength and molded material is carefully selected in consider of absorption characteristic. By controlling the first pulse and designing a circuit for avoiding field concentration during plating, the molded component is successfully processed without any damages. Using this method, the world’s smallest human detection sensor, “NaPiOn” has been developed.

In order to realize a micro mechanical relay, a new technology of adjusting the characteristics of relays by laser has been developed. While IT-related mechanical relays have been increasingly miniaturized, the mechanical adjustment system by using the conventional spring material bending has already come to its limit in the adjustment process of relays. In attempt to overcome this situation, the application of laser forming, which is able to deal with miniaturization and is not influenced by spring back, was examined. However, as the beam spring used for relays involves a thin thickness and high thermal conductivity, the conventional technique of repeating laser irradiation, which induces damage of the surface and residual stress, to the same parts couldn’t adjust the displacement with accuracy. A technique that changes beam path in repeating laser irradiations was then applied. Consequently, with a minimal number of times of irradiation, the characteristics of relays can be adjusted by using laser without causing damage to the surface.

In order to examine the dependence of ITO(Indium Tin Oxide) thin films on wavelengths of laser at ablation, the first, second, third and fourth harmonic of diode-pumped Nd:YLF laser were employed respectively. Patterning was performed successfully at any wavelength. The laser fluence was controlled by defocusing of beam. We made comparisons with each fluence for ablating ITO layer on substrate glass, and observed surface of the glass and edge of groove formed by laser etching. Near the groove, much debris was deposited. So we examined the effects of various sealed gases having molecular weight (e.g. He, N₂, Ar). The amount of debris was reduced by only He gas. Additionally we measured index of absorption by ITO and substrate glass for lights. The range for wavelengths was swept from ultraviolet to infrared. In conclusion, we recognized that the removal of ITO was more efficient with increase of absorption of lights.

ITO film, which is a kind of transparent conductive film, has been used for LCD, PDP and so on. This film is mostly removed by wet etching method. However, this method needs many chemicals, numbers of process and large-size equipments. On the other hand, laser beam processing can achieve the dry process without chemicals and drastically reduces the number of process. Therefore, selective removal of ITO film on glass substrate by LD pumped Q-switch SHG YAG laser is experimentally investigated. Electric insulation across machined groove was successful. Better groove shape can be obtained by accurate control of defocused distance and feed rate under a constant average power. Using SHG YAG laser makes it possible to remove only ITO film without any damage to glass material as substrate, since SHG YAG laser of 531 nm in wavelength is easy to transmit the glass material. When laser beam is irradiated from ITO film to glass material, a non-removed portion of ITO film remains at the bottom of groove under long defocused distance condition. On the other hand, backside irradiation method, in which laser beam is irradiated to ITO film through glass material, can prevent from remaining a non-removed portion, since absorption of laser beam occurs from the boundary part between ITO film and glass material.

On laser drilling of printed circuit board, one-dimensional non-steady heat conduction problem of two-layers composed of resin and metal was analyzed with the finite element method (FEM), considering resinous evaporation. Validity of analysis method was verified by comparing with experimental results. The main conclusions are as follows: (1) Proportionality between latent heat of evaporation and absorptivity can be obtained using the experimental results of removal quantity when resin is thick enough. These values can be estimated simultaneously by comparing analytical results by FEM and experimental results. (2) An equation for rough estimate of maximum removal velocity was derived. (3) Removal quantity is proportional to the number of shots, but its proportionality is lost after layer thickness reaches to absorption length, yielding smear in practical use. Residual smear is caused by heat conduction to substrate during pulse. (4) Removal quantity depends on fluence most, but hardly depends on repetition rate. When resin thickness is larger than absorption length, removal quantity per pulse is proportional to fluence. (5) Removal velocity becomes larger with shorter pulse width. When resin thickness is smaller than absorption length, residual thickness increases as pulse width becomes long.

Present study was performed to determine the welding conditions for sound welding, efficiency and process of bead formation using Yb fiber laser for ultra thin metal foil (SUS304, thickness: 10~60μm). The influence of assist gas was investigated by the measurement of bead width at different gas flow rate and the conditions of keyhole welding was estimated with metal foil. Relationship between experimental results and thermal conduction calculation based on moving line heat source model was also investigated. Sound lap welding of 20μm to 30μm thickness was obtained.

In order to investigate the applicability of laser micro welding to the fabrication of medical devices, SUS304 stainless steel and Ti-Ni based shape memory alloy biomaterials wires were micro spot melted by using YAG laser. By the optimization of laser conditions such as laser power or pulse duration, sound spot melted wires free from any defects were prepared and the width of the melted metal was reduced to about 0.3mm for the 0.35mm diameter wires. Compared with the SUS304 wires, melting of shape memory alloy wires needed more precise control of laser conditions although it needed smaller power input. Melted metal exhibited a rapidly quenched microstructure. The spot melted wires showed comparable tensile strength or super-elastic behavior with base materials. Besides, by the microstructural observation and corrosion test in a quasi biological environment, corrosion resistance was estimated to be hardly degraded by spot melting. Crosswise or parallel joints was also successfully prepared by laser spot welding of wires, suggesting the laser micro welding is applicable to the fabrication of biomedical devices.

The past three years has seen the evolution and maturation of Clearweld technology as a tool which is readily employable for the transmission laser welding of thermoplastic and some thermoset polymers using near infrared lasers and inks uniquely chosen and targeted to absorb the laser light at the intended laser weld joint in order to efficiently and rapidly effectuate the weld. This paper will discuss the novel and useful transmission values and minimal haze characteristics of the welded polymeric part as compared to the unwelded component parts both in the nascent state and in parts prepared for the laser welding operation. Further presentation will be made relative to the color hue recession toward neutrality and the goal of colorlessness as the parts are taken from these prewelded states to the welded final part. Among the polymeric materials discussed are polycarbonate, cast polymethylmethacrylate, nylon and polyester. Detailed attention is given to the Clearweld process used in these welding operations as well as to the employed welding equipment, ink deposition, laser welding process parameters and full spectral characteristics of all components and welded parts. Mechanical characteristics of resultant welds are offered for verification and comparison of the process integrity as a novel and very useful manufacturing tool.

A new system has been built allowing the fast control of the laser welding process in conduction regime. Based on a traditional Proportional Integral Derivative (PID) analysis, the system can regulate millisecond laser pulse (Its response time is 90 microseconds). Besides, the interaction in this regime has been monitored with different diagnostics. Visible signal above target, IR signal from surface and visualization from CCD camera have been correlated as function of laser power density to distinguish the different phases of interaction (pure conduction, vaporization and/or plasma). With this experimental set up, the detector used for control process could be calibrated. The integration of the system is shown for watch parts assembly.

The presence of melt during the laser drilling process always signifies a balance between an efficient material removal in molten form and a reduction of quality due to recast on the hole walls and near the crater entrance. Earlier investigations have demonstrated that by reducing the laser pulse duration the amount of produced melt can be decreased and hence, the precision increased. Nevertheless, they also demonstrate that melt can never be avoided completely. Therefore, to achieve an optimum balance between efficiency and quality by a preferably complete expulsion of melt the physical fundamentals of its generation and ejection have to be understood. By applying several different analytical and numerical models ranging from simple estimations to multi-dimensional simulations, the authors will outline the peculiarities of the melt formation and dynamics during the drilling with short and ultra-short laser pulses. Since these calculations demonstrate the importance of the consideration of melt acceleration and geometric aspects, special interest will be taken in these matters. While the evaporation stops soon after the laser pulse, the melt ejection may continue until the complete solidification of the material. For a better understanding and verification, the results of the models will be compared to experimental data.

Laser drilling is one of the promising methods for manufacturing fine-patterned and noble devices in electronic packaging. In order to realize 3D packaging by via hole drilling on Si chip devices by short pulse laser without damage, we developed the basic method predicting heat damage based on thermal conduction by finite element analysis. Quantitative prediction of heat affected zone (HAZ) where temperature exceeds the threshold value was employed in variety of process parameters such as power density, pulse width and beam profiles of laser. Numerical result showed that melting zone (MZ) size by a single shot of excimer laser was nearly same as irradiated area size in case of 7 μm of irradiated diameter, 10.2 J/cm² of fluencies and 50 ns to 1 μs of pulse width, and that HAZ size was independent of pulse width consequently. It was found that spatial beam profile did not affect MZ size although HAZ size was slightly changed. Thermal degradation was predicted to be enhanced in case that the beam was irradiated near the edge of chip.

This paper presents a new CO₂ laser technology for precision microfabrication applications. The laser produces short (microsecond) pulses at very high pulse repetition frequencies (PRFs). In contrast, most commercial CO₂-laser micromachining applications employ one of two type of CO₂ lasers: RF-excited with external pulse modulation, and TEA lasers. The laser technology presented here produces pulses sharing some of the characteristics of the TEA CO₂ laser, but is capable of delivering them at much higher PRFs (20-100 kHz). Microfabrication applications to date are primarily microdrilling in common electronic circuit board and IC packaging materials, including unreinforced, glass-fiber reinforced, and particle-filled epoxies. These materials are processed using pulse energies lower than those generally used by conventional CO₂ laser designs, and at speeds typically 1.5 to three times as fast as achieved by conventional CO₂ laser drills.

The waterjet-guided laser processing is a thermal cutting process in which the laser beam is used as the machine tool for cutting and the fine waterjet plays a role as an optical waveguide. The laser beam is guided in the waterjet stream with the full reflection that takes place at the boundary between water and air, in a manner similar to glass fibers. The waterjet also has the function of waveguiding and removing the cut products. The diameter of the waterjet can be controled between 50 and 200 μm. The diameter of laser beam is completely utilised. The useful length of waterjet is usually approximately 50 to 100 mm. The type of laser used is a pulsed Nd:YAG laser. The advantages of waterjet-guided laser processing are (1) no Z-axis control, (2) narrower cut widths down to 50 μm, (3) very small heat affected zone, (4) a little oxidation of the cut edges, and (5) no assist gas for cutting. A reseach was carried out for the new industrial application which is unsuitable by conventional laser cutting.

A new type of f-theta lens has recently been developed for microvia laser drilling of multilayer printed circuit boards. It employs a diffractive/refractive hybrid lens which has a blazed surface-relief microstructure on an aspheric surface. By introducing that hybrid lens for CO₂ laser system, and by stopping the use of germanium that is optically much sensitive to temperature, the f-theta lens that consists of all zinc selenide lenses is obtained with its optical performance stable on temperature. Achromatic properties against the wavelength fluctuations of actual lasers are also achieved. A prototype is fabricated through the development of single point diamond turning of hybrid surfaces. The performance of the lens is first examined by measuring wavefront error with a tunable infrared interferometer. The results show diffraction-limited performance at all conditions, including different temperatures (up to 50°C) and wavelengths. The temperature dependence of the focal length of the lens is also measured and found to be 5 times as insensitive to temperature as that of a conventional one. Laser drilling experiments are performed for a polymide film on copper foil. The result shows good uniformity of hole size and circularity all over the 50×50 mm² scan field.

Using a 1.06 μm wavelength YAG laser, we have produced holes in glass-foam substrates. We have used three types of glass-foam made from 1-mm-thick quartz. The first type, called S1, contains 5% foam ranging in size from 2.0-50 μm. The second type, called S2, contains foam ranging in size from 0.1-0.5 μm. The third type, called S3, contains 12% foam ranging in size from 100-200 μm. We have drilled holes in these three types of glass-foam at pulse widths of 0.5-1.2msec and power of 0.5-3.0J. Only the S1 substrate is capable of creating a through hole at a power up to 0.8J. The height of the pile-up increases 15-40 μm with increasing power. The S1 substrate has better machinability than S2 and S3. The S1 substrate is suitable for laser beam machining.

Micromachining using the DPSS 3rd Harmonic Laser (355nm) has outstanding advantages as a UV source in comparison with Excimer lasers in various aspects such as maintenance cost, maskless machining, high repetition rate and so on. It also has the greater absorptivity of many materials in contrast to other IR sources. In this paper, the process for micro-drilling of through and blind hope in Cu/PI/Cu substrate with the UV DPSSL and a scanning device is investigated by both experimental and numerical methods. It is known that there is a large gap between the ablation threshold of copper and that of PI. We use the multi path for through hole with high energy density and we use Archimedes spiral path for blind hole with different energy densities to ablate different material. Furthermore, Matlab simulations considering the energy threshold of material is performed to anticipate the ablation shape according to the duplication of pulse, and FEM thermal analysis is used to predict the ablation depth of copper. This study would be widely applicable to various laser micromachining applications including through and blind hole micro-drilling of PCB, and micromachining of semiconductor components, medical parts and printer nozzles amongst others.

We studied the microscribing of Al2O3 ceramics by a diode-pumped Nd:YLF laser. The third harmonic of a Nd:YLF laser (λ=349nm) was used. The scribing characteristics such as groove width, groove depth and debris height were measured. By varying the focal position of the beam at fixed laser power, we observed three regions characterized by the color and the profile of the irradiated area. Region I was marked by high debris and black color due to thermal effects at the focusing position, Region II showed brown color and good scribing properties with low debris height at a slightly defocused position, and finally Region III was unchanged color (original white) but little scribing due to low power density at the defocused position. These results show that an optimum energy for scribing ceramics exists. Finally good scribing without color change may be possible by adjusting the irradiation energy.

Laser ablation of GaN thin film and GaN/Sapphire structure for the application o flight emitting diodes (LEDs) has been performed. Edge quality and surface roughness of the specimens are compared using scanning electron microscopy (SEM) and atomic force microscopy (AFM) after laser processing by the 3^rd harmonic Nd:YAG laser, KrF excimer laser and Ti-sapphire femtosecond laser. Dependence of laser ablation rate on the processing parameters, such as laser fluence, scanning speed and pulse repetition rate with the laser irradiation is also investigated. Device characteristics of the specimens after the laser microprocessing are also analyzed.

We describe the diagnostics of the particle dynamics during thin film deposition and the nano-particle formation by pulsed laser ablation in a background gas. Oxidation process during the deposition of the Ce-substituted yttrium iron garnet thin films in an oxygen background gas has been investigated by the laser-induced fluorescence spectroscopy (LIF) and the ZnO nano-particle formation process has been observed by the Rayleigh scattering imaging, in order to understand the relationship between the deposition conditions and the film properties. Furthermore, in order to investigate the earlier stage of the nano-particle formation process in the ablation plume, a new imaging technique, named as re-decomposition LIF (ReD-LIF) was proposed and its signal characteristics were investigated theoretically and experimentally. It was proved that ReD-LIF can visualized the small clusters, which are difficult to be visualized by any other methods.

Time-of-flight (TOF) mass and optical emission spectroscopies have been performed on the ablation plume from α-FeSi₂ alloy target under KrF excimer laser irradiation at a fluence of 0.35-2.5J/cm² to characterize the mass, kinetic energies and excited states of the ejected species. According to the TOF mass measurements in vacuum, the most prominent species were Si and Fe atoms and ions over the entire fluence range, in addition to Si dimer. At 0.4-0.7 J/cm², only neutrals of Si, Fe and Si₂ with the kinetic energy of around 0.2eV were observed. At the fluences above 0.7J/cm², doubly and singly charged Si and Fe ions appeared abruptly increased their number density and kinetic energies from 6 eV at 0.7 J/cm² to over 100 eV at 2.5 J/cm². Consistent with the TOF mass spectra, the optical emission lines stemmed from the monatomic Si and Fe as well as Si dimer in the wavelength range of 240-800 nm in vacuum. On the other hand, we confirmed some luminescent lines appeared only in helium atmosphere of 10 Torr, suggesting the cluster formation such as FeSi.

We have investigated dynamics of ablated species in ZnO plume under ArF excimer laser irradiation with emission imaging and spectroscopy, and discussed the effect of a surrounding inert gas. Surrounding He or Ar gas strongly cools down the plume and encourages aggregation of ablated species, which is visualized by second laser irradiation to the plume.

Transient transmitted power through thin Si substrate (0.35 mm) irradiated with pulsed SHG-(532 nm) and fundamental (1064 nm) Nd:YAG lasers has been calculated to simulate laser marking process using FEM (finite element method). Dependence of attenuation factor on temperature and wavelength is considered. Fraction of transmitted power with a fundamental Nd:YAG laser drastically decreases by irradiation with three pulses from 40% to 5%, while the transmitted power with an SHG-Nd:YAG laser is negligible over the pulses.

Two measurement methods to determine the rate of neutral free radical production by the photo-deionization of negative ion beams ( PDINIB ) are introduced. These methods, namely, photoelectron-current measurement by low-frequency electro-modulation probe ( PMMP ) and measurement of decrease in the negative-ion beam current ( DNIC ) were employed to evaluate the production rate in a trail surface-processing apparatus developed in the author’s laboratory utilizing a steady-flux refined beam of neutral free radicals produced by the PDINIB procedure. A ⁶³Cu^- negative ion beam of kinetic energy E_i varied up to 15 keV was irradiated with a 514.5 nm visible light beam from a 25 W CW Ar⁺ ion laser. The detection limit of the production rate by the PMMP setup was as high as 6×10⁹/s under the condition that E_i = 15keV, the negative ion beam current I_i = 4 μA, and the laser power P = 6W. The DNIC method is simpler but less reliable than the PMMP method owing to larger uncertainty resulting from the fluctuation of the negative-ion beam current.

Ab initio molecular orbital methods were applied to screening tests of the organometallic source materials suitable for the photo-assisted low-temperature growth of stoichiometric epitaxial films of group-III nitrides. The molecular properties of dimethylgalliumnitrene ((CH₃)₂GaN), dimethylaluminumnitrene ((CH₃)₂AIN), and dimethylboronnitrene ((CH₃)₂BN) were examined in terms of the stability and the reactivity. Also clarified were the photolytic and the pyrolytic decomposition mechanisms of the corresponding azides. Based on these theoretical analyses, we confirmed the applicability of beams of (CH₃)₂GaN and (CH₃)₂AIN produced by the method of photo-dissociation of energetic compound beams to the epitaxial growth.

The dynamics of a charged two-dimensional colloidal system in the presence of a one-dimensionally modulated laser field is studied by using Brownian dynamics simulations. The present model consists of interacting point particles in two dimensions, including effects of screened Coulomb force, laser-induced periodic force, Stokes drag force, and thermal noise. For the case of low particle density and the laser potential periodicity commensurate with the mean interparticle distance, computer simulation results find four characteristic phases with three crossover as a function of the laser field strength.

Laser-induced backside wet etching of fused silica plates using aqueous solutions of naphthalene-1,3,6-trisulfonic acid trisodium salt (Np) and pyranine (py) was performed upon KrF excimer laser irradiation at 248 nm. The two etching media show different etching behavior with changing laser fluence and medium concentrations. Well-defined line-and-space and grid micropatterns at 1 μm scale were fabricated using an aqueous solution of Np and the etched pattern was free of debris and microcracks.

Basic principles of laser assisted process of fiber etching for scanning near-field optical (SNO) probes formation and control technique are presented. The thermal and temporal regimes are considered in order to provide stable reproducibility and high quality of a tapered end of the optical fiber. Problems of adequate definition of the scanning imaging properties of a SNO probe are discussed. Thus an optical method of far-field registration and processing together with a new autoelectronic emission method are considered for solution of the task of a subwavelength SNO probe aperture measurement and estimation of its apparatus function.

This paper describes the fabrication of micro-channels in resin for micro-fluidic devices by a UV laser. Quartz wafers are coated with a 20μm thick BCB resin. Micro-grooves for micro-channels are fabricated into the BCB resin by a KrF excimer laser. The groove bottom is 100m wide at a pulse width of 20nsec, fluence of 1.3mJ/cm²/pulse, and overlap of 98.9%. The wafer surface serves as the bottom face of the groove. Moreover the side wall angle is 72°. Furthermore, the grooves are covered with laminate films to prevent leakage of the liquid samples. A thermoplastic film or a heat-hardening resin film is used as a laminate film. Laminating conditions are: roller temperatures of 120°C, pressure of 0.8MPa, and laminating speed of 0.2m/min. The thermoplastic film coats the groove perfectly. On the contrary, the heat-hardening film does not sag into the groove, resulting in an open-are cross-sectional ration of 80%. Furthermore, the open-area-ratio becomes 100% through a heat-curing process at a temperature of 120°C for 30min. The through holes are made in the laminate film by a KrF excimer laser. Inlet pipe for a micro-pump are inserted into the hole.

Laser-assisted chemical vapor deposition is investigated as a useful method to fabricate micrometer size carbon rods and to directly write an arbitrary deposit pattern. The deposits were produced on graphite substrates from pyrolytic decomposition of ethylene by irradiating focused argon ion laser beam at a wavelength of 514.5nm. Depending on whether the laser beam is stationary on a fixed location or scanning over the substrate, a growth of micro carbon rod or a direct writing can be achieved, respectively. Micro rods with various diameters, ranging from about 30 to 400 micrometers, with an aspect ratio of as large as 100 are fabricated using this method. Generally, a larger diameter rod is obtained as the laser power increases. Averaged growth rate of the rod varies from approximately 4 to 35 micrometer per second and increases with both gas pressure and laser power. Laser direct writing of carbon film is achieved by controlling scanning speed of the laser beam. When the scanning speed is too small, the film transforms into a rod growing toward the laser beam while a continuous film is obtained as the scanning speed and the deposition rate is balanced.

Direct-Write techniques have the potential to revolutionize the way miniature sensor devices and microbattery systems are designed and fabricated. The Naval Research Laboratory has developed an advanced laser-based forward transfer process for direct writing novel structures and devices comprising of metals, ceramics, polymers and composites under ambient conditions on both ceramic and plastic substrates. Using this forward transfer technique, we have demonstrated the ability to rapidly prototype various types of physical and chemical sensor devices, and microbatteries. The laser forward transfer process is computer controlled which allows the design of the devices to be easily modified and adapted to any specific application. Furthermore, the same process enables the fabrication of complete sensor or power-source systems by incorporating the passive electronic components required for sensor readout or power management. Examples are provided of various types of miniature sensors, and prototype alkaline and Li-ion microbatteries fabricated using this technique.

Meso-scale devices that contain micro-scale features have been fabricated in a photosensitive glass ceramic material using a novel combination of direct-write pulsed UV laser irradiation and variable exposure processing. This merged nonthermal, direct-write laser processing technique involves the precise variation of the laser irradiance during material patterning. The controlled variation of the laser exposure dose is used to selectively alter the chemical etch rate of the processed regions in the glass ceramic. Consequently, variegated and proximal high and low aspect ratio structures can be fabricated on a common substrate. The microstructures can be created in a single, simultaneous chemical batch etch without the need for a complex masking sequence or ablation. For example, adjacent microstructures with aspect ratios of 2:1 and 20:1 have been laser patterned via variable exposure processing and concurrently fabricated on a shared glass wafer following a single chemical etch step. Our current variable exposure technique enables the conversion of CAD patterns and corresponding laser irradiance information into realized microfabricated structures in glass or ceramic form that retain feature sizes within 10% of the desired dimensions. We have applied this technique to fabricate various structures that may be useful in far-infrared (IR) or terahertz (THz) devices that require high aspect ratio features.

Laser-ablation-based microfabrication technology is applied to fabricate micro-electro-mechanical-systems (MEMS) devices on polymer substrates. A micromachining apparatus is designed and developed which includes a 355 nm laser, an uncoated focusing lens, computer-controlled precision x-y-z stages and in-situ process monitoring systems. Concentric rings microstructures are formed by efficiently changing the laser intensity distribution. Tiny via holes and micro-nozzles with different diameters have been obtained by low power laser direct drilling. Optical microscopy and scanning electron microscopy (SEM) are used to evaluate the processing results at different laser processing parameters. This method has the advantages of low-cost and time-saving in circle via holes fabrications. Potential applications of this novel MEMS fabrication technique are also briefed.

Photo-stereolithography is one of the most typical rapid prototyping and manufacturing technologies which enables to fabricate 3D objects easily, quickly and automatically from CAD drawings. For these advantages, it has been expected of application to the micromachining. But the conventional method is not suitable for such usage. Because it is based on the so-called laser scanning and laminating process that can’t achieve high accuracy and rapidness together. We propose a new photo-stereolithography method using a liquid crystal display (LCD) as the live-motion mask. Simultaneous exposure using the LCD live-motion mask makes it possible to precisely fabricate each layer at high speed without scanning. A complex 3D structure is fabricated by the continuous laminating of thin layers. Ideally, this method realizes the nonlaminate fabrication. In order to verify a feasibility of proposed method, we performed the fundamental experiments. As a result, the lateral resolution reached 5 μm. We fabricated the pyramidal shape and the bevel gear shape with both lateral and vertical resolution of 5 μm. Although the size was a few mm order, it took only about 20 minutes to finish fabricating. These experimental results show that the LCD live-motion mask method corresponding to the continuous laminating satisfies the two requirements of accuracy and rapidness.

The current paper presents the results of recent studies of the effects of laser processing parameters on the microstructure and surface topology of laser grooved Ti-6Al-4V surfaces used for biomedical applications. Laser micro-grooves are produced using a diode pumped solid state (DPSS) lasers at 355 nm and different pulse repetition frequencies (PRF). The underlying microstructures and surface topologies of the grooves are then characterized using scanning electron microscopy (SEM). Laser/material interaction mechanisms are discussed and optimal laser processing parameters are developed. The implications of the microstructural and topological features are then assessed for cell/surface interactions and adhesion.

We demonstrate a few examples of laser trapping and manipulation technique being applied for the measurements of small forces in the range of fN-pN and for laser microfabrication. We discuss prospective principles applicable for future nano/micro-mechanical tools. Elastic properties of microtubules of 24 nm in diameter were determined, a gold particle of 0.25 μm in diameter was laser trapped and manipulated. Paramagnetic microspheres were DNA-anchored to a glass substrate for measurement of elastic properties of DNA by evanescent light scattering. Also, a gold particle was attached to DNA and laser manipulated. The motion of the DNA molecule controlled. The spring constant of the DNA was determined by using thermodynamical analysis of evanescent light scattering.

We have developed an all-solid-state 252nm coherent light source for laser cooling of silicon atoms with tow-stage highly efficient frequency conversions with external cavities. With the coherent light source, it is possible to manipulate the atomic motion of the silicon atoms towards nano-process applications. In this paper, deflection, collimation, and axial velocity selection of the silicon atomic beam with the coherent light source are discussed.

Cobalt nanoparticles have been fabricated by laser ablation of metal target at laser wavelengths of 1064 nm and 532 nm. The target was immersed in water during the ablation. Size of the resulted nanoparticles was determined by optical microscope and field emission scanning electron microscope (FESEM). It was observed that the minimum particle was 6 nm in diameter. Ultraviolet to visible (UV-vis) spectra and photoluminescence (PL) spectra were applied to characterize the optical properties of these products. In order to investigate the magnetic properties, the particles were spread on clean substrates for vibrating sample magnetometer (VSM) measurement. It was fond that magnetic properties of generated cobalt nanoparticles were obviously influenced by their sizes. Effects for the different laser wavelengths on particle formation were compared.

Nanometer-sized particles of silicon and titanium dioxide were generated by Nd:YAG laser ablation of solid substrates in a low pressure atmosphere. A low-pressure differential mobility analyzer (LP-DMA) was used to control the size of generated particles. The LP-DMA and a transmission electron microscopy (TEM) were used to measure the change in size distribution and morphology of nanoparticles with laser power and pressure. Finally, we succeeded to synthesize the almost spherical nanoparticles of 2-50 nm in diameter.

Metal nanoparticles films were prepared by a gas deposition technique couple with the nanosecond pulsed Nd:YAG laser ablation of two kinds of metal targets. Two generated nanoparticles were insitu mixed in the near space of the targets in the generation chamber and transported by a helium carrier gas to the deposition chamber and deposited on a substrate to form electric devices such as a resistor, a capacitor, wiring, etc., composed of nanoparticles composites. The electrical resistivity and capacity of the devices were measured. The relationship between the experimental conditions such as ambient pressure and laser fluences and the electrical properties of each device were analyzed. A heater was produced as an example of the application of a resistor.

Crystalline and c-axis oriented zinc oxide (ZnO) films with grain structure were deposited on sapphire substrates by pulsed-laser deposition (PLD) technique. The deposited films had cut off at about 390 nm. Photoluminescence (PL) was observed with excitation at 355 nm by third harmonic wave of Nd:YAG laser. In addition, the behaviors of the nanoparticles condensing in the gas phase of PLD were observed by imaging and spectroscopic methods of ultra-violet Rayleigh scattering (UV-RS) and laser-induced incandescence (LII).

Polyperinaphthalenic organic semiconductor (PPNOS) nano-particles are prepared by excimer laser ablation (ELA) of a 3, 4, 9, 10-perylenettracarboxylic dianhydride (PTCDA) target using XeCl excimer laser beams. Heterojunctions of the films consisting of nano-particles of PPNOS with Si wafers are fabricated. Well rectifier property is obtained for the junction of the PPN with a n-Si substrate. Current versus voltage curves of the heterojunction in the dark and under illumination show that the junction is promising as a photovoltaic cell. Furthermore, the films are applied to anode electrodes for ultra thin rechargeable Li ion batteries. In-situ Raman spectroscopy of the films under lithium ion doping and undoping is performed to elucidate the storage mechanism of lithium ion at cis-polyacetylene-type (phenanthrene-edge) of PPN structure.

We deposited SiO₂ films with different refractive indices by pulsed laser deposition with silicone targets. The deposition rate could control the refractive index of the films. The refractive index of the film deposited at 0.05 nm/pulse is greater than that of the film at 0.1 nm/pulse. The origin of the refractive index changes was to be film porosity changes, which was observed by surface profile meter. The deposited films were free of impurities such as OH and carbon. Thus, a 0.4- μm-thick SiO₂ cladding film deposited at 0.1 nm/pulse was firstly formed on the whole surface of Si wafer, and then a 1- μm-thick SiO₂ core film at 0.05 nm/pulse was fabricated in a line on the sample. Again, the sample was coated with a 0.1- μm-thick film at 0.1 nm/pulse. The sample functioned as an optical waveguide for a 633-nm line of He-Ne laser.

A novel technique for synthesizing a diamond-like carbon (DLC) film by pulsed laser deposition (PLD) is proposed. In the technique, additional lasers irradiated the plume in order to increase the density of the ionic carbon. By irradiating with an ArF excimer laser, the emission intensity of the atomic carbon was increased greatly. By irradiating with the third harmonic output and the fundamental output of an Nd:YAG laser, the emission intensity of the atomic and ionic carbon also increased greatly. The sp³ content increased from 51% without to 76% with two additional irradiation of the fundamental output of two Nd:YAG laser beams. The differences in the binding energy and surface morphology between the films with and without the irradiation of the additional lasers to the plume were observed by X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM), respectively.

LiNbO₃ thin films were deposited by pulsed-laser deposition (PLD) method. Crystalline and transparent films were deposited on sapphire substrates at 400 °C and in 100 mtorr of oxygen gas pressure. The waveguide properties, which were waveguide mode and loss, were measured by prism coupling method. Droplet less film was obtained with low ablation laser fluence and without scanning of ablation laser. The smallest waveguide loss was 32.9 dB/cm at present.

Photocatalytic titanium dioxide (TiO₂) thin films with large specific surface area were deposited on Si wafers by pulsed laser deposition with sintered TiO₂ targets in oxygen gas atmosphere. Angular distributions of the number of droplets and the film thickness were examined. The surface roughness and the film thickness depended on the oxygen gas pressure. Photocatalytic effect of the films deposited at various substrate temperatures was evaluated by photobleaching of methylene-blue-aqueous solution. The TiO₂ film deposited at the substrate temperature of 250°C was anatase-type crystal and this film indicated the highest photocatalytic effect.

Thin film of Zn_xCd_1-xS mixed crystal is applicable to short-wavelength optical devices from visible to UV region because of various band gaps. Using the pulsed laser deposition (PLD) method, we first produced the Zn_xCd_1-xS mixed crystal thin films. The surface morphology, the composition of x and the crystal structure of the thin films were observed with SEM, EDAX and XRD respectively. The lattice constant corresponding to (002) plane of hexagonal crystal linearly depends on x following the Vegard’s law. The crystal grains of the Zn_xCd_1-xS thin films have the c-axis perpendicular to the film surface and good crystallinity. The optical transmittance was measured at room temperature so that the optical band gaps of direct transition continuously increase from 2.43 eV (510 nm) to 3.63 eV (340 nm) with x. The continuous change of the band gap indicates solid solution formation.

A thin film is a very attractive material in applications for capacitor material. Since the capacitance of multi layer capacitor is proportional to the number of dielectric layer and it is inversely as thickness, making thickness of film thin has a double advantage, in order to enlarge the capacitance. This research was performed thin film sizing and growth control of BaTiO₃, which are used as a dielectric. The increase of capacitance is predominant over the present value of 1nF.

Optical properties of nitrogen-doped diamond-like carbon films deposited by pulsed laser deposition at room temperature are investigated. Three series of diamond-like carbon films are prepared by KrF excimer laser ablation of graphite with assistance of different nitrogen sources. Series 1: nitrogen gas of 99.999% purity is applied to react with carbon species. Diamond-like carbon films with nitrogen content of ~0.5-1.7 at.% are prepared at different nitrogen gas pressures (10^-4-10^-1 Pa). Series 2: a radical beam source is used for providing an atomic nitrogen beam. Diamond-like carbon films with nitrogen content of ~1.0-5.4 at.% are synthesized at nitrogen gas pressure of 10^-3-10^-2 Pa. Series 3: a 3-cm ion source is employed for supplying an active nitrogen ion beam. Diamond-like carbon films with nitrogen content varying from 8.0 to 14.3 at.% are deposited. The optical properties of the synthesized diamond-like carbon films are characterized by ultraviolet-visible spectrometry. Investigation indicates that the different nitrogen sources have different effects on the optical properties of diamond-like carbon films.

The latest development in industrial fabrication of low temperature poly silicon by high power excimer laser annealing is presented in respect of two different aspects. To begin with, the precondition for todays generation 4 LTPS TFT LCD plants was fulfilled by recently improving the line beam annealing method by introduction of a 300W Lambda Physik excimer together with up to 370mm MicroLas line beam optics, integrated in an complete Japan Steel Works excimer laser annealing system for higher throughputs in substrate recrystallization. Secondly, an outlook on a new substrate illumination method is given, the so called sequential lateral solidification (SLS), which has already been developed to a level enabling industrial exploitation. The SLS method is not only very promising, because it can decrease substrate recrystallization time by a factor of 10 in comparison to the currently used line beam method, it also improves the performance of the poly-Si film by approximately a factor of two in terms of increasing the field effect mobility of free charge carriers to up to 300cm²/Vs. This will possibly allow production of CMOS devices on the panel, which is so far not possible in case of the LineBeam method.

A new dry cleaning methodology named laser-induced shock cleaning has been applied to remove the chemical-mechanical polishing (CMP) slurries from silicon wafer surfaces. After CMP process using the slurries, the slurry particles should be removed from the surface in order to avoid the circuit failure and enhance the yield. The well-distributed remaining silica particles were attempted to remove from the surface by using laser-induced plasma shock waves. In order to evaluate the cleaning performance quantitatively, the number of particles on the wafer surfaces were measured by surface scanner before and after cleaning. It was found that most of the silica particles on the wafer surface were removed after the treatment of laser-induced shock waves. The average removal efficiency of the particles was 99% over. It was found that cleaning performance is strongly dependent on a gap distance between laser focus and the surface and a suitable control of the gap is crucial for the successful removal of the particles.

Liquid-assisted cleaning technology utilizing a nanosecond laser pulse is effective for removing submicron particulates from a variety of solid substrates. In the technique, saturated vapor is condensed on the solid surface to form a thin liquid film and the film is evaporated explosively by laser heating. The present work studies the role of liquid-film evaporation in the cleaning process. First, optical interferometry is employed for in-situ monitoring the displacement of the laser-irradiated sample in the cleaning process. The experiments are performed for estimating the recoil force exerted on the target with and without liquid deposition. Secondly, time-resolved visualization and optical reflectance probing are also conducted for monitoring the phase-change kinetics and plume dynamics in vaporization of thin liquid layers. Discussions are made on the effect of liquid-film thickness and dynamics of plume and acoustic wave. The results confirm that cleaning force is generated when the bubble nuclei initially grow in the superheated liquid.

The present paper describes a study on the crystallization of a sol-gel derived precursor ZnO film during and after the irradiation of an excimer laser. The temporal change of the structure of ZnO films was discussed based on the time-resolved signal of a reflected and a transmitted laser beam during the excimer laser irradiation. The surface morphology of the films was analyzed by atomic force microscope (AFM). The pulse-to-pulse changes of integrated signals reflected the surface conditions of the ZnO film. In time-resolved measurement, significant changes of both signals were observed during the first pulse.

We have developed an anti-reflection (AR) coating technique designed for high power carbon dioxide (CO₂) lasers that has low absorption and high resistance to humidity. This was achieved by performing ion-assisted deposition (IAD) using a Xe ion beam to apply BaF₂ and ZnSe used as coating materials with extremely low bulk absorption coefficients. It was found that to achieve highly compact BaF₂ thin films with low absorption on polycrystalline ZnSe substrates, both a surface flatness treatment using Xe ion bombardment and an optimized IAD condition of relatively low ion energy up to 200 eV are required. The absorption of the new (BaF₂/ZnSe) AR coated ZnSe lens is 0.10 to 0.12%, approximately half that of conventional (ThF₄/ZnSe) AR coated lenses. The new lens has both excellent anti-aging performance and a high resistance to humidity.

Frequency-conversion techniques such as SHG, THG and FOHG with nonlinear optical crystals are indispensable for the applications of solid-state lasers to precision microfabrication. It is well known that the conversion efficiency is very sensitive to the temperature rise of the crystal, which is induced by laser absorption. In this study, temperature dependence of SHG efficiency has been investigated theoretically, supposing Nd:YAG laser of uniform intensity and KDP (KH₂PO₄) crystal. The coupling problem composed of complex wave amplitude equations and one-dimensional heat conduction equation was analyzed. The complex wave amplitude equations were derived considering the absorption of laser in the crystal. The main results obtained are summarized as follows: (1) Decreasing of SHG efficiency due to laser absorption for the single pulse irradiation to a crystal of 10 mm long, is less than five percent. (2) When SHG efficiency is higher, temperature-rise of the crystal is smaller. Because absorption coefficient for the fundamental wave is larger than that of the second harmonic. (3) When the temperature of crystal rises due to repeated irradiation of pulse laser, SHG efficiency fluctuates and decreases gradually. Remarkable inverse-conversion of SHG appears during laser irradiation with high power density. (4) As either pulse width or irradiation time becomes longer, analytical SHG efficiency agrees with the approximate results obtained under the simple phase-mismatching conditions.

ZnSe Diffractive Optical Element (DOE) is one of the advanced optics which utilizes the optical diffraction phenomena by fabricating a micron order pattern on polished mirror-like surface of ZnSe polycrystal substrate. Various applications for a carbon dioxide (CO₂) laser material processing such as beam-splitting, beam-shaping and beam-homogenizing are available. The micro pattern of ZnSe DOE is fabricated by the photolithography and reactive ion etching (RIE) technique. Its optical property is highly dependent on the depth precision of microfabricated pattern. In RIE by using BCl3 as the etchant gas we have achieved an etching technique to maintain the smooth surface of the ZnSe polycrystal with minimal etching rate dependency on the crystal orientation of each crystal grain. The surface roughness is 2nm Ra before etching and 5 nm Ra after about 4 microns depth etching. This good roughness brings better depth precision. With these etching technique beam-splitting ZnSe DOE with less than 10% intensity uniformity of splitted beams is successfully obtained and it can be put to use for practical CO₂ laser hole drilling.

A new type of three-dimensional measurement systems based on Conoscopic Holography is steadily gaining ground against older techniques. ConoProbe, the point sensor is found today on many applications of Q.C. measurements, digitizing, reverse engineering and in-process inspection. Its precision and capacity to measure many materials and geometries previously poorly measured had convinced many OEM and integrators to switch to this new technology. The ConoLine, line sensor, is aimed mainly to in-line inspection and quality control. Distance measurement is used in some applications of high power lasers as for example for inspection before or after cutting or drilling. The ConoProbe is used for such an application with much benefit for the user. Indeed, one of the main advantages of the ConoProbe is its capacity to view through the lens of the high power laser, either YAG or CO2 and to measure accurately the distance using the laser’s own lens. The collinear geometry removes many artifacts related to triangulation probes. Moreover, by deporting the ConoProbe from the region of the laser lens, up to one or two meters, the user recovers much important space for integration purpose and reduces the need for protection of the ConoProbe.

In a PWB laser drilling system, an aspheric beam shaper, which converts single-mode Gaussian beam into beam with uniform irradiance profile is widely used. This beam shaper is very sensitive to decentering of the input beam, which is caused by the instability of beam pointing. It degrades the irradiance profile uniformity of the output beam and the processing quality. To solve this problem, we develop a beam pointing compensation optical system. This system contains a newly designed collimator which have a function to project the origin of the pointing vector of the laser beam to the input surface of the shaper in addition to the conventional function to control the diameter and the wavefront curvature of the laser beam. We analyzed the performance of the collimator by simulation, and confirmed that the irradiance distribution of output beam was not degraded by the instability of the beam pointing. Also, we confirmed its effects by the optical experiments.

For the first step of our study, temperature dependence of SHG conversion efficiency has been analyzed theoretically on the supposition of uniform intensity beam. The results are presented in the paper appeared in the same proceedings. In this paper, the analysis was carried out two-dimensionally with an axisymmetrical model based on the previous one-dimensional model, applying the paraxial approximation. Two-dimensional temperature distribution induced by laser absorption and variation of the conversion efficiency of KDP crystals were analyzed quantitatively during repetition irradiation of pulse laser. Main results are summarized as follows: (1) Depending on SHG and its inverse conversion, temperature of the crystal with Gaussian beam irradiation fluctuates remarkably in the axial direction in the central part of crystal. (2) During repetition irradiation of Gaussian beam, heat conduction in the radial direction prevents temperature from rising in the central part of crystal. (3) The conversion efficiency for a Gaussian beam stays relatively high for a long period, compared with that for uniform beam.

The JAERI FEL group has successfully discovered, and realized the brand-new FEL lasing of 255fs ultrafast pulse, 6-9% high-efficiency, one gigawatt high peak power, a few kilowatts average power, and wide tenability of medium and far infrared wavelength regions at the same time. The new lasing was named to be “high-degeneracy superradianct lasing of FEL”. Using the new lasing, we could realize a powerful and efficient free-electron laser(FEL) for industrial uses, for examples, pharmacy, medical, defense, shipbuilding, semiconductor industry, chemical industries, environmental sciences, space-debris, power beaming and so on. In order to realize such a tunable, highly-efficient, high average power, high peak power and ultra-short pulse FEL, we need the efficient and powerful FEL driven by JAERI compact, stand-alone and zero-boil-off super-conducting rf linac with an energy-recovery geometry. Our discussions on the FEL will cover market-requirements and roadmap for the industrial FELs, some answers from the JAERI compact, stand-alone and zero-boil-off cryostat concept and operational experience over these 10 years, our discovery of the new highly-efficient, high-power, and ultra-short pulse lasing mode, and the energy-recovery geometry.

A novel 351 nm picosecond-range pulsed, master-oscillator-power amplifier laser system, specially designed for an advanced mask repairing system LM700A, capable of repairing photomasks for 130 nm-design rule 1G DRAMS, has been developed. The front-end of the laser system is a diode-pumped, simultaneously active-mode-locked and Q-switched Nd:YLF laser and is capable of emitting short light pulses variable in the range between several ten- and several hundred picosecond. Extracted pulses from the mode-locked and Q-switched pulse trains are amplified by a double-pass amplifier and are subsequently frequency-converted to 351 nm by using LBO crystals for high-precision photomask repairing. Optimum irradiation conditions for opaque defect repairing have been investigated for by varying pulse duration to satisfy the stringent requirements such as for minimum repairing accuracy better than 30 nm, high transmission with minimum surface damage, minimum wall roll-up, etc. Mid-range pulses having around 200 ps have been found to be optimum to realize high quality repairing.

On the basis of highly efficient Yb:fiber amplifiers, a new technology platform for compact and nearly maintenance-free laser sources from the femtosecond to the nanosecond time scale has been developed, allowing their application-customized use in industrial laser material processing. The core of this technology is the patented use of multimode fibers with TEM₀₀ output characteristics, enabling high and efficient amplification while maintaining high quality of the output beam. First, we review the fiber laser amplifier developments in the femtosecond pulse regime. Then, we present for the first time a picosecond seed source, Yb fiber amplifier laser design. Next, we present a completely new laser seeder/amplifier design, enabling online temporal tuning of laser pulses between 4 and 20 ns without changing pulse energy by utilizing high-speed control circuitry to adjust pulse duration, repetition rate and pulse energy independently. Pulse length can be optimized to process a given dimension of a sample structure that needs to be modified. Pulse shape can be controlled to produce almost rectangular pulses with <1.5 ns rise times. The resultant pulses can be transported by a polarization-maintaining delivery fiber for easy integration and use in material processing applications. Finally, we describe a few examples of micromachining using pulses from this new, flexible, fiber-based nanosecond laser source.

The noise and mode-locking phenomena of a hybrid soliton pulse source (HSPS) utilizing Gaussian apodized filter Bragg grating is described. The HSPS is modeled by a time-domain solution of the coupled-mode equations including spontaneous emission noise, and relative intensity noise (RIN) is calculated using numerical solutions of these equations. It is found that transform limited pulses are not generated with Gaussian apodized grating even if system is properly mode-locked at the fundamental frequency. If transform limited pulses are not obtained, a noise peak in the RIN spectrum does not occur at the fundamental frequency.

Ge-SiO₂ thin films with extremely high photosensitivity against excimer laser light were fabricated by plasma enhanced chemical vapor deposition method. Direct formation of channel waveguide was successfully confirmed only by irradiation with excimer laser through a Cr mask pattern, which was previously coated on the slab-waveguide by sputtering method. Bragg gratings with high diffraction efficiency were also printed in the waveguide by another laser irradiation through the phase mask. Channel waveguides with Bragg gratings, on the other hand, were fabricated on the glass ceramic substrates with negative thermal expansion coefficient. Doping of B₂O₃ to Ge-SiO₂ glass film was effectively suppressed the temperature drift of the stop band (dλ/dT)of the grating. The dλ/dT attained in this study was 5pm/°C, which was less than ½ of those for commercially available waveguide gratings. The waveguides with gratings using the photosensitive oxide thin films should be a promising candidate for future low cost and reliable optical access network.

The modifications included on PET by an excimer laser radiation or a low pressure plasma as well as their ability to improve A1-PET adhesion were investigated. For this purpose, surface roughness, chemical composition, surface wettability and adhesion properties of PET were studied depending on the process parameters. Both treatments can significantly enhance the adhesion but the surface change responsible for the improvement was different for each pretreatment.

A multiwavelength excitation process using F₂ and KrF excimer lasers for high-efficiency and high-speed refractive index modification of fused silica is demonstrated. We find that this process is essentially superior to conventional single-wavelength F₂ laser processing. The multiwavelength excitation process achieves twice of diffraction efficiency compared with that of single-wavelength F₂ laser irradiation sample at the same number of total photons supplied to the sample. This high-speed and high-efficiency modification is realized within ±50 ns of the delay time of each laser beam irradiation. In addition, the refractive index change of the multiwavelength sample was increased to 8.2×10^-3, which is 1.78 times larger than that of single-wavelength F₂ laser irradiation sample at same irradiation time. This superiority of the wavelength excitation process is attributed to resonance photoionization-like process based on excited state absorption in fused silica.

When a pair of clean solid surface are brought close to the atoms distance in the vacuum, the solids were bonded by the gravitation and binding force. Such a way of bonding is called a surface activated bonding. In this work, a laser irradiated to a couple of copper plates surface under various conditions of laser irradiation. The surface oxidation layer and organic layer were removed by laser ablation. After the irradiation, a couple of copper plates surface get close to each other. The possibility of the bonding was examined by AFM.

We found out that GeO₂-B₂O₃-SiO₂ thin films fabricated by plasma enhanced chemical vapor deposition method exhibited not only large photo-induced but also thermo-induced refractive index increases, both of which were above 10^-3. The former was observed after irradiation with KrF excimer laser, and the latter was induced by annealing at 600°C. The thermo-induced refractive index increase was closely related to the formation of thermo-induced absorption bands during the annealing, and could be suppressed by the laser irradiation prior to the annealing. Bragg gratings were printed in the films by the laser irradiation through the phase mask without H₂ loading. The diffraction efficiency decreased rapidly by the annealing up to 500°C, but drastically increased after the annealing at 600°C. The thermo-induced gratings couldn’t be erased by the repeated heat treatments between room temperature and 600°C at all. Considering the suppression of thermo-induced index increase by the laser irradiation, this grating was expected to have the reverse pattern of refractive index compared to that of the as-printed one, and might be applicable to the highly reliable optical and sensing devices.

Laser-induced technological chemical processes can significantly contribute to the development of new methods for micro treatment of materials and hence to the broadening of the application spectrum of laser microtechnology. In this paper three typical laser-activated chemical technological methods in liquids, gases and solids and their possible applications are presented and discussed: 1) Laser-induced liquid-phase jet-chemical etching of metals. In this method, laser radiation which is guided from a co-axially expanding liquid jet-stream initiates locally on a metal surface a thermochemical etching reaction, which leads to a selective material removal at high resolution (<1μm) and quality of the treated surface; 2) Local photon-plasma induced synthesis of thin film coatings. This technological method is based on thermochemical CVD processes taking place in a photon-initiated stationary plasma maintained in the electromagnetic optical field of a high-power cw-CO₂ laser radiation. This method allows synthesis of thin-film coatings in the open-air atmosphere without using vacuum or reaction chamber; 3) Laser-induced photochemical modification of the optical properties of polymers. This method is based on the local controllable change of the polymer structure leading to modification of the refractive index in the treated area. By numerous independently adjustable laser radiation parameters, for instance wavelength and irradiation dose, the modification process can be controllably driven in order to generate desired functional properties.

In this paper some recent results are presented about the photochemical modification of polymers by UV-laser-irradiation which leads to a controllable and local change of the refractive index in the irradiated area of the polymer surface. The exact modification mechanism and its relation to the modified refractive index have been investigated on the basis of PMMA used as a UV-modifiable model polymer with good optical quality. This new UV laser-assisted technology for photochemical modification of the optical properties of UV-modifiable polymers like PMMA or PMMI and their fluorinated derivates permits the fabrication of a wide range of integrated-optical components like strip waveguides, power splitters, (Mach-Zehnder-)interferometers, Bragg gratings and other dispersive structures. These integrated-optical elements are crucial for the realization of dispersive components like WDM or AWG, which have a wide application in the optical sensor and information technology. The optical and functional properties like loss rate or mode propagation of some selected integrated-optical components have been investigated and are discussed in this article.

NiTi Shape Memory Alloy (SMA) is with great potential for actuation in microsystems. It is particularly suitable for medical applications due to its excellent biocompatibility. In MEMS, local annealing of SMA is required in the process of fabrication. In this paper, local annealing of Ni₅₂Ti₄₈ SMA with excimer laser is proposed for the first time. The Ni₅₂Ti₄₈ thin film in a thickness of 5 μm was deposited on Si (100) wafer by sputtering at room temperature. After that, the thin film was annealed by excimer laser (248nm KrF laser) for the first time. Field-Emission Scanning Electron Microscopy (FESEM) and Atomic Force Microscopy (AFM) were used to characterize the surface profile of the deposited film after laser annealing. The phase transformation was measured by Differential Scanning Calorimeter (DSC) test. It is concluded that NiTi film sputtering on Si(100) substrate at room temperature possesses phase transformation after local laser annealing but with cracks.

It is a high challenge to fabricate glass microstructures in Photonics and LCD industries. Different from direct ablation with ultrafast or short wavelength lasers, laser-induced-plasma-assisted ablation (LIPAA) is one of the potential candidates for transparent substrate microfabrication with conventional visible laser sources. In the processing, laser beam goes through glass substrate first and then irradiates on a solid target behind. For laser fluence above target ablation threshold, plasma generated from target ablation flies forward at a high speed. At a small target-to-substrate distance, there are strong interactions among laser light, target plasma and glass substrate at its rear side surface. With target materials deposition on glass surface or even doping into the substrate, light absorption characteristic at the interaction zone is modified, which causes the glass ablation. LIPAA is used to get color printing of characters, structures and even images on the glass substrate. It is also used to obtain the glass surface metallization for electrodes and circuits fabrication. Potential application of this technique to fabricate functional microstructures, such as micro-Total-Analysis-System (TAS) for DNA analysis and holographic diffuser for IR wireless home networking, is also discussed.

In this paper investigation of using frequency-converted diode-pumped solid-state laser for substituting conventional industrial machining processes like in the MST is presented. For industrial application a decreasing of the processing time is demanded. This study shows that the pulse energy of current available DPSS lasers is nearly sufficient to meet the demands for industrial laser cutting and selective ablation processes.

A coloring method using a laser system has been proposed in our laboratory. This method has the features as follows. i) The processing objects are plastic materials such as acrylic, nylon, epoxy, polyester etc. ii) Heating the dye solution by the irradiation of a laser, a material can be dyed at a local area of laser irradiation. iii) The images which printed by this method have persistence for erasing such as washing or rubbing. iv) Since the absorptivity of CO₂ laser to the dye solution is high, a slap, RF excited CO₂ laser was used as a heating source. This method, however, could be expressed only one-color image. In order to perform expression based on the digital image, not one-color but the colors printing of the image has been required. In this study, the innovative laser coloring method has been introduced for the colors printing. This method combines the laser processing dots which are possessed different colors. For example, by combining the dots of two colors, another color printing can be created. Otherwise, by changing the combining rate of the dots of two colors, more other color printing has been possible. A color printing on plastics using the innovative laser coloring method has been successfully attempted.

This paper makes a report on the results of experimental analyses about the relation between drilling performance about alumina ceramics and focusing characteristics, as first step for clarifying of drilling mechanism of ceramics by CO₂ laser. The results are as follows: · (1) When the focal point is set inside of the work, the shape of holes is made 50 to 55% deeper and 10 to 15% smaller than these when the focal point is set outside of the work. (The distance between work surface and focal point is +/-0.2mm.) It seems to be able to concentrate higher energy when the focal point is set inside of the work. · (2) Spot diameter under 95 μm with the focusing angle (7.5-8 degrees) is necessary to make deep holes. was clarified. From this, it seems that to make deep holes does not only need higher energy density, but also need smooth elimination of molten work. The result of these analyses was applied to new scribing system to develop scribing performance. The scribing speed of alumina ceramics was improved by 20%.

The manufacturing of micro parts is mainly done in silicon, where manufacturing technologies from electronic production can be used. In cases, where the mechanical and structural properties of silicon are not sufficient or the costs of silicon micro parts can not be effort, other materials like polymers and metals have to be used. In this cases laser technologies can be a versatile tool for the production of tools, like moulds and stamping and embossing tools or the micro parts directly. Short pulse lasers, especially frequency-tripled, diode pumped Nd:YAG-lasers with a high beam quality offer the possibility to ablate these materials with high quality. With a spot size of about 10 μm, high fluences (> 100J/cm²) can be achieved, so that the materials are vaporized without or with only a small amount of molten material. This technique is applicable for the production of micro tools with accuracies < 10 μm at three dimensional microstructures. With optimized machining parameters the surface roughness can be reduced to R_a≤0.1 μm. Depending on the material and the machining parameters the slicing thickness is in the range of 1 to 10 μm.

Phase manipulated ultrafast laser pulses and temporally tailored pulse trains with THz repetition rates are promising new tools for quality micromachining of brittle dielectric materials, allowing to adapt the laser light to the material properties for optimal processing quality. Different materials respond with specific reaction pathways to the sudden energy input depending on the efficiency of electron generation and on the ability to release the energy into the lattice. Loss and cooling mechanisms in the electron population, surface charging, as well as the strength of the electron-phonon interactions control the effectiveness of the energy deposition into the lattice. Knowledge of the response times of materials establishes a guideline for using temporally shaped pulses or pulse trains in order to optimize the structuring process with respect to efficient material removal and reduction of the residual damage. The sequential energy delivery with judiciously chosen pulse trains may induce softening of the material during the initial steps of excitation and change the energy coupling for the subsequent steps. We show, that this can result in lower stress, cleaner structures, and allow for a material-dependent optimization process.

In recent years, femtosecond (fs) laser ablation has attracted much interest in both basic and applied physics, mainly because of its potential application in micromachining and pulsed laser deposition. Ultrashort laser ablation have the capability to ablate materials precisely with little or no collateral damage, even with materials that are impervious to laser energy from conventional pulsed lasers. The extreme intensities and short timescale at which ultrashort pulsed lasers operate differentiate them from other lasers such as nanosecond laser. In this work, we investigate the expansion dynamics of Cu (copper) plasma generated by ultrashort laser ablation of pure copper targets by optically examining the plasma plume. Time-integrated optical emission spectroscopy measurements by using intensified charged couple detector array (ICCD) imaging were used to detect the species present in the plasma and to study the laser-generated plasma formation and evolution. Temporal emission profiles are measured. Our interest in the dynamics of laser-generated copper plasma arises from the fact that copper has been considered as a substitute for Aluminum (Al) interconnects/metallization in ULSI devices (for future technology). It is important to know the composition and behavior of copper plasma species for the understanding of the mechanisms involved and optimizing the micro-machining processes and deposition conditions.

For the purpose pf determining optical properties of high-density plasmas created by ultra-short-pulse lasers, we have measured reflectivity with the pump-probe method. Nominal parameters of pump laser were 248nm, 300fs, and 10¹³~10¹⁴W/cm2 and those of probe beam were 745nm and 120fs. In the case of Al target and a normal incidence probe beam, the reflectivity decreased with time after arrival of the pump pulse. The duration of this change in reflectivity was apparently longer than pulse duration of pump beam at high intensities, while it was almost the same as pulse duration of pump beam for lower irradiance. A change of absorption during the pump pulse and non-linear dependence of resistivity on temperature could not explain these observations. A simple layered structure model was proposed in which heated layer penetrates into cold region with time and interferometric reflection occurs. This model could qualitatively explain the experimental results. Ellipsometric parameters were also measure with a single-shot based four-detector system. There were different time histories observed for the ratios of I(0,0), I(π/2,0) and I(π/4, π/2). This result also implies the plasma has some layered structure.

Laser ablation of Cu, Al, Fe, Zn, Ni, Pb, and Mo by short pulse laser (800nm wavelength, 70fs pulse duration, 0.01-28 J/cm² fluence range) in air was studied. Three different ablation thresholds were distinguished in all metals. The lowest ablation threshold was of one order of magnitude lower than the one observed previously. In the fluence range of 0.018-0.18 J/cm² the ablation rate was ≈0.01 nm/pulse. A dependence of the threshold on the pulse duration was demonstrated in the range of 70 fs- 5 ps for cupper. As the laser pulse duration increased, the ablation threshold had the tendency to be higher. A periodic structure was observed at the bottom of the crater in all metals. The spacing d of the patterned structure was determined to be d=300±40 nm for 0.07 J/cm² and d=600±40 nm for 0.22 J/cm². The spacing depended on the laser fluence rather than on laser wavelength.

Generation of the multiply charged ions and molecular ions have been investigated using synchronous irradiation of high intensity and ultrashort pulse of Ti:sapphire laser and fourth harmonics of Q-switched nanosecond pulse of Nd:YAG laser to carbon target. The ion current wave forms have been analyzed by means of the time-of-flight mass measurement. The formations of cluster ions were detected due to the irradiations of both high intensity and ultrashort pulse of Ti:sapphire laser and fourth harmonics of Q-switched nanosecond pulse of Nd:YAG laser.

Laser ablation process of aluminum with the fourth harmonics of Nd:YAG laser is simulated, using the modified molecular dynamics method, which has been developed by Ohmura and Fukumoto. It has been clarified in the previous studies that there are two types in laser ablation process. One is explosive ablation and the other is calm ablation. In this paper, the ablation processes of these two types were visualized first by classifying the ablated atoms by the start time of scatter. It was cleared that the transition of kinetic and potential energies of ablated atoms and the energy ratio used for ablation to the absorbed energy depend on these ablation types. It was also verified that the transition of the number of ablated atoms and lumps of atoms also depend on the ablation types.

Electron emission from the surface of copper target irradiated with femtsecond pulsed laser (wavelength 800nm, pulse width 100fs) was measured at the atmospheric pressure. A tiny metal probe was used to detect the electric potential made by the charged particles. It was found that the energy of emitted electrons became higher gradually when laser irradiation was repeated on the same spot.

During the past few years research groups demonstrated the potential of femtosecond pulses for ultra-precise machining. Soon industry became interested in the new technique which promises to get rid of precision deficits occurring when using longer pulses. As possible applications drilling of nozzles, structuring of tribological surfaces and sharpening of diamond tools are considered among others. Initial investigations of such industrial applications soon showed, however, several unexpected quality problems such as formation of recast, ripples and irregular hole shapes even in the femtosecond pulse regime. After describing the problems this contribution will present some progress in fundamental understanding of the ultrafast ablation process. On the basis of this knowledge technical means have been developed allowing to achieve an unprecedented level of accuracy at acceptable expenses. The latter being strongly influenced by the shortness of the laser pulse, a comparison between pico- and femto-second regime will be presented.

Large scale, true three dimensional (3D) microchannel structures have been fabricated in photosensitive glass by femtosecond (fs) laser. In general, the microchannel fabricated inside glass by scanning focal spot of fs laser perpendicularly to the laser propagation direction gets an elliptical shape with a large aspect ratio of its cross section, which is undesirable to most of micro total analysis systems (μ-TAS) or micro fluidic devices. In this paper, we describe how to improve the aspect ratio of the fabricated microchannel by using advanced irradiation methods of fs laser.

Femtosecond laser ablation using phase-shifted laser beam is reported. Phase-shifting method is a unique method to modify the Gaussian intensity profile into closely adjacent pair of the high intensity peaks. The phase-shifting was accomplished by the use of reflecting plane-mirror whose plane has a step of quarter of the wavelength. The calculation of intensity profiles using Fresnel diffraction theory shows a steep intensity changes in a very closed area. In the experiment of femtosecond laser ablation using phase-shifted beams, debris attachment has been observed both surround area and the central part corresponding to the phase edge. We discuss the anomalous enhancement of debris attachment at the central part.

Interfered femtosecond laser beams split by a diffractive optics was used to fabricate micro and cyclic structures. The process was done on the surface of samples, as polystyrene, slide glass, sapphire, and gold thin film. On each sample, a line of periodic dot structure with a period of about 6.25 μm was fabricated. The length of workpiece was 6 mm at maximum, and which is longest structure fabricated by a laser ablation using interfered femtosecond laser beams.

Surface treatment of stainless steel and other metals is presented using subpicosecond laser pulses at 248 nm. Applying diffractive optical masks combined with a reflective imaging system sub-micron size features are generated on the sample surface. During the experiments different types of diffractive elements are used. The imaging properties of an amplitude mask consisting of crossed lines and a 2 level diffractive phase element (DPE) are compared to obtain micro hole arrays. Ablated structures with diameters between 300 nm and 1,5 μm are presented. The ultrashort pulse UV laser system applied for surface texturing comprises a Ti:Sapphire front end system and a specially developed excimer amplifier module generating 300 fs pulses at 248 nm with an average power of close to 10 W. Using the above mentioned diffractive optical elements and the newly developed excimer module operating at 300 Hz allows high precision texturing of large surfaces opening up new possibilities in industrial applications.

In recent years industry has shown a growing interest in the field of micro-structuring of surfaces on macroscopic workpieces. Several applications to improve the tribological properties of surfaces are known as well as various techniques for printing and embossing. Today the availability of lasers with the appropriate reliability for industrial applications limits the pulse durations to nanoseconds or longer. However, the quality of the resulting structures is limited, especially in metals, due to the formation of melt that has to be removed by additional post-processing. Several earlier published experimental results have shown that it is possible to avoid melt deposition by shortening the pulse duration into the femtosecond regime. This contribution will present results in the field of microsurface-structuring of metals with ultrashort laser pulses. It was found that femtosecond pulses alone are not sufficient to obtain structures free of recast. Melt free material processing is only possible in a restricted parameter window. With current laser sources, process speed is too slow for the economical use in the industrial production. To explore the potential of high repetition rate lasers, experiments with an appropriate laser source were carried out.

The ultrashort laser microstructuring of multilayer gratings for X-Ray optics is presented in this paper. A micromachining system operating with a KrF laser at 0.5 ps pulse duration and a high reduction ratio (÷30) optical projection system was used to etch grating structures on Si/Mo multilayer with lateral period of 1.5 m. Scanning Electron Microscopy, Atomic Force Microscopy and X-ray Reflectivity were used to characterize the microetched patterns. Gratings with over 100 lines of 0.8μm×700μm were fabrication at low laser fluences (<600mJ/cm²). The roughness of the grating was measured from 0.5 nm to 1 nm for the shallow grooves (depth=4-5nm). The X-Ray reflectivity measurements confirmed the well-preserved multilayer structure. The ω scans around the 1^st Bragg maximum have shown diffraction peaks up to the 3^rd order on both sides with positions corresponding to the grating period. The use of sub-picosecond laser pulses minimizes the thermal affected zone and enhances the quality of the etched features. The ultrashort laser micromachining is advantageous for the fabrication of high spatial resolution microstructures required in the X-Ray optics industry.

In recent years, the microfabrication technology has splendidly been developing in the various industrial applications. It is effective that laser wavelength and pulse duration in laser microfabrication are shorter on the viewpoints of enhancement of spatial resolution and improvements of microfabrication quality. In this paper, we report on the ablation characteristics of the chromium thin film on quartz substrate (what is called Cr binary photomask) by using femtosecond laser (130fs Ti:sapphire laser). The diffraction pattern of laser intense distribution is observed in image printing with the optical rectangular slit, as the result of effects of minimized thermal diffusion with femtosecond laser pulses. We have obtained the Cr ablation without substrate damage with sufficiently wider ablation laser power range for multiple laser pulse irradiation, though ablation of the large band gap materials like quartz is easily caused due to the multi-photon absorption process in femtosecond laser irradiation. Further we indicated that ablation region does not depend on the diffraction limit with the femtosecond laser pulses.

The detailed study of the role of air pressure in deep hole drilling by femtosecond and picosecond intense laser pulses (Ti:Al₂O₃ and Nd:YAP lasers) was performed in the range 1÷1000 mBar. Steel sample plates were mostly tested, experimental data obtained for ceramic materials is also presented. The following ablation parameters were measured and analyzed: ablation rates and their dependence on the channel depth, ablated crater morphology, optical transmission in channels after through hole formation. Both percussion and helical drilling regimes were used. Special attention was paid to two strong gas assisted effects typical of sub-picosecond and sub-nanosecond material ablation, which are low threshold gas breakdown in deep channels and nonlinear interaction of ultra-short intense pulses with air resulting in conical emission. Unwanted aspects of both phenomena were shown to disappear in a moderate vacuum of ~100 mBar. A new approach to formation of such a vacuum in drilled channels was also proposed and experimentally modeled using ultra-high repetition rate nanosecond laser pulses.

Linearly- and circularly-polarized femtosecond (fs) Ti:sapphire laser pulses at 800 and 267 nm were focused in air to ablate hard thin films of TiN and DLC deposited on stainless steel plates. The morphology of the thin film surfaces that were ablated by the fs laser pulses at an energy fluence slightly above the ablation threshold was observed and characterized with a field emission-scanning electron microscope. With the linearly-polarized light, arrays of fine slender granular structure were produced on the ablated surface, which were almost oriented to the direction perpendicular to the laser polarization. On the other hand, the circularly-polarized light is found to form fine dot structures on the film surface. The size of these surface structures was 1/10 ~ 1/5 of the laser wavelength used and was observed to decrease with a decrease in the laser wavelength. It should be noted that the size of surface structures observed is much smaller than that of the well-known surface ripple patterns produced by the laser-induced surface electromagnetic wave.

Femtosecond laser has been expected as a new tool for the industrial usage in particular to material micromachining. We are developing the dicing technique with femtosecond laser ablation for the ultra thin semiconductor substrates, which are 50 μm thick or less. In this research, we performed drilling for 50 μm thick silicon substrate with femtosecond laser (π=120 fs, λ=800 nm, F=1 kHz) as the basic experiment for dicing, focusing on the influence of a double-pulse irradiation on the processing characteristics. The double-pulse irradiation for 18 shots of 10 μJ/pulse at the pulse separation time from 10 to 20 ps showed the remarkable reduction of the height of the molten layer around the drilled hole (<0.5 μm). At the same time, however, the ablation depth was the minimum (<2.3 μm). The surface inside the hole got smooth as the pulse separation time of more than 3 ps. We supposed that the second pulse in a double-pulse should generate the another ablation on the surface and its high pressure should prevent the ablated materials by the first pulse from flying out of the hole.

There is a proven potential of ultra-short laser pulses for precise cutting of all kinds of materials. Especially with regard to miniaturizations in the semiconductor industry, even industrial high-speed cutting processes nowadays aim for the precision of femtosecond laser systems. However, when working with a typical spot-focused laser beam on current standard systems, the processing speed is too low for an industrial cutting of larger parts as, for instance, silicon wafers. Apart from improving the laser systems with regard to pulse energies and repetition rates, it is therefore crucial to realize that material ablation can also be influenced by other process parameters. In case of straight microcuts e.g. in silicon wafers, a new approach is a beam shaping strategy using certain arrangements of cylindrical lenses. This can significantly contribute to an increase of the achievable cutting speed, and at the same time reduce the minimal kerf width while using the highest available laser power. We present examples of such kerfs in thin silicon wafers using a system of cylindrical lenses in comparison to a customary achromatic lens, and provide information about the focusing process and the chances and challenges entailed.

Due to the low energy threshold of photodisruption with fs laser pulses, thermal and mechanical side effects are limited to the sub μm range. The neglection of side effects enables the use of ultrashort laser pulses in a broad field of medical applications. Moreover, the interaction process based on nonlinear absorption offers the opportunity to process transparent tissue three dimensionally inside the bulk. We demonstrate the feasibility of surgical procedures in different fields of medical interest: In ophthalmology intrastromal cutting and preparing of corneal flaps for refractive surgery in living animals is presented. Besides, the very low mechanical side effects enables the use of fs-laser in otoralyngology to treat ocecular bones. Moreover, the precise cutting quality can be used in fields of cardiovascular surgery for the treatment of arteriosclerosis as well as in dentistry to remove caries from dental hard tissue.

Teflon, polytetrafluorethylene (PTFE), is an important material in bioscience and medical application due to its special characteristics (non-flammable, anti-adhesive, heat-resistant and bio-compatible). The advantages of ultrashort laser processing of Teflon include a minimal thermal penetration region and low processing temperatures, precision removal of material, and good-quality feature definition. In this paper, laser processing of Teflon by Ti:Sapphire femtosecond laser (780 nm, 110 fs), Nd:YAG laser (532 nm, 7 ns) and CO₂ laser (10.6 μm, 10 μs) has been investigated. For femtosecond laser processing, clear ablation takes place and provides high-quality groove on Teflon surface. Both the groove depth and the width increase as the laser fluence increase, and decrease almost linearly as the scanning speed increase for laser fluence below 5.0 J/cm². For Nd:YAG processing, Teflon surface roughness is improved but no clean ablation is accessible, which makes it difficult to micromachine Teflon by Nd:YAG laser. For CO₂ laser processing, laser-induced bumps were formed on Teflon surface with controlled laser parameters. The physics mechanisms for different pulse duration laser processing of Teflon are also discussed.

We have been studying the refractive index changes and vacancies that are induced in silica glass by the irradiation of ultrashort laser pulses. By scanning the laser beam in glass we can form, 1) 3-D shapes of waveguides, 2) arrays of nano-scale (sub-micron) vacancies, called voids, and 3) 3-D shapes of long holes with microscopic diameters, and 4) Bragg gratings with microscopic sizes. In this paper, we report on the waveguides formed by femtosecond laser pulses. We may also talk about the cross-sectional asymmetry of the waveguides formed by linearly-polarized laser pulses. The formation of the photo-induced waveguides is normally accompanied by the filamentation, the self-trapping of laser beam due to nonlinear optical effects. We make use of this filamentation to form the waveguides. We also report on the formation of submicro-meter or nano-meter vacancies, called voids, with femtosecond laser pulses. We are going to talk about the possibility of forming asymmetric shapes of nano-scale voids. The asymmetry of voids results from the beam profile. We controlled the profile by inserting apertures before the focusing lens. The asymmetry leads to the polarization dependence of diffraction from the array of voids. We finally report on the formation of 3-D shapes of long holes with microscopic diameters and Bragg gratings in glass. The Bragg gratings were formed in soda-lime glass. We succeeded in forming a series of three Bragg gratings. The formation of grating inside glass was confirmed by diffraction experiments and chemical etching of polished cross-sections.

Time-resolved dynamics of plasma formation and bulk refractive index modification in silica glasses excited by a tightly focused femtosecond (110 fs) Ti:sapphire laser (λ_p=800 nm) was first observed in situ. The newly proposed pump-probe measurement with perpendicularly linear polarized beams was used to study the dynamic of both plasma formation and induced refractive index bulk modification. The energy variation of transmitted probe beam with time delay, which propagates through the induced plasma is measured. At the pre-breakdown domain, the lifetime of induced plasma formation is ~15 ps and structural transition time for forming the refractive index change is ~10 ps. At the breakdown domain, however, the lifetime of induced plasma formation is ~35 ps and structural transition time for forming the optical damage is ~35 ps. We found that the process of refractive index bulk modification is significantly different from that of optical damage. According to the electron spin resonance (ESR) spectroscopic measurement, it was found that the defect concentration of SiE’ center increased significantly in the modified region in related to that of the region without modification. From the diffraction efficiency of Kogelnik’s coupled mode theory, the maximum value of refractive index change (Δn) was estimated to be 1.1×10^-2. By the scanning of silica glass on the optical X-Y-Z stages, the fabrication of the internal grating with refractive index modification was demonstrated in silica glass using tightly focused femtosecond laser. The experimental results will be helpful to understand the physical mechanism of the plasma and structural transformation induced by tightly focused high-intensity femtosecond lasers in transparent materials.

Holes of few tens of micrometers have been drilled through a glass plate by femtosecond laser pulses. A femtosecond laser (Clark-MXR, CPA 2001) which delivered 775 nm, 150 fs pulses at 1 kHz was used to machine holes through glass plates of about 150 micrometer thick. Laser pulses were focused by a plano-convex lens on to the glass plate. An electric shutter controlled number of irradiating laser pulse. Entrances of the drilled hole were crack-free but shell-like cracks appeared at exit end of them. Shapes of the drilled holes were examined in detail by taking replicas of them using silicon-rubber based material. Small debris scattered around the drilled hole and its deposition range depended on the laser peak power. Development of the hole with increasing pulse numbers showed several distinct stages. The first few tens of pulses drilled a shallow, flat bottom hole with a deeper channel at the center of a flat bottom. Then, the flat bottom and the channel emerged into a deep, funnel shaped hole with tapered wall. The hole became deeper and finally went through to the rear side at certain pulse numbers, which depended on pulse energy and focusing conditions. Position of the focus relative to the glass surface affected the shape of drilled holes. This means that the shape of the drilled hole is very sensitive to laser intensity distribution with a well defined threshold and would suggests the possibility of drilling designed-shape holes with proper diffractive optics for modifying the intensity distribution of the laser light.

When femtosecond laser pulses are tightly focused inside the bulk of transparent materials, the intensity in a focal volume becomes high enough to produce submicrometer-scale structural modifications. This damage was shown to be a cavity or a void surrounded by densified material. An array of voids can be used as optical data storages or gratings. We showed the control experiment of the positions and shapes of voids insider transparent materials with femtosecond laser pulses. We have demonstrated the experiments involving optical movement of a void along the optical axis by translation of the focal spot with femtosecond laser pulses. Irradiation of femtosecond laser pulses moves a void inside calcium fluoride and silica glass without any mechanical translations of the optical system up to 2 micron. In this paper, we show that the shapes of voids can be controlled by the spatial profile of incident laser pulses. Finally we show that the fabrication of a Fresnel lens inside silica glass.

We describe a true three dimensional (3D) microfabrication of photosensitive glass by applying a femtosecond (fs) laser which works at fundamental wavelength. First, designed microstructure was written into the glass sample by a tightly focused fs laser beam (wavelength 775nm, pulse width 145±5fs, repetition rate 1kHz); next, this sample underwent a programmed heat treatment; finally it was immersed into 10% hydrofluoric (HF) acid to take an ultrasonic bath. By this approach, true 3D microstructures with embedded microchannels and microcells are directly formed inside the glass matrix, without extra bonding or adhering procedures in those planar fabrication techniques. Such an approach combines the advantages of high precision in laser microfabrication and cost-effectiveness in chemical processing, therefore, could be a promising tool in futuristic manufacture of micro total analysis systems (μ-TAS) and micro fluidic devices.

We have already shown that the refractive-index change is induced by a self-trapped filament of ultrashort laser pulses in silica glass. In this paper, we investigate the dependence of refractive-index change on polarization of incident laser pulses in silica glass. In the experiment, we focused linearly polarized pulses inside a sample of silica glass. We polished the sample and etched by 5% HF solution to observe the cross-sectional view of the regions of refractive-index change that are perpendicular to the filament. The observation with a scanning-electron microscope shows that the cross-section is elliptical and the long axis was parallel to polarization direction of incident laser pulses. The ellipticity was 0.85. We fabricated gratings to estimate the index ellipsoid of the region of refractive-index change. We confirmed that the index ellipsoid was uniaxial and negative. The optic axis was parallel to the axis of the filament and the birefringence was 1×10^-3.

Lime-glass and silica-glass plates with thickness of 100 μm were drilled with a ultra-short pulse laser(780nm, 150fs pulses at 1kHz). The surface of the glass plate at front side and rear side were observed by SEM, and the transmitted laser power though the glass plate was measured for both of glass. The appearance of the drilled hole of lime-glass was compared with that of silica-glass. The drilling characteristics of lime-glass and silica-glass plates with thickness of 100 μm by femto-second laser pulse were studied. On rear side, the crack occurred before drilling through the plate. The crack on the rear side occurred in lime-glass at smaller shot number than in silica-glass. The transmitted laser power ratio was decreased with increasing laser intensity. Interesting phenomenon that the lower glass plate began to be drilled before the upper glass plate was drilled through, when two glass plates with air gap of 12 μm were drilled.

Interaction of highly excited electrons in nonequilibrium states with the lattice in metals has been studied using femtosecond pulse lasers. Two ablation regimes are identified as the optical and energy penetration by examining the fluence dependence of ablated depth per pulse. Surface structuring and surface compositioning of metal substrates using a femtosecond pulsed laser irradiation is characterized with the SEM images as a function of laser fluence. Laser ablation provides a mechanism to facilitate an achievement of a nano- and microstructuring on the metal surface. Based on our results, ultrashort pulse provides wide competitive range of applications in surface structuring and patterning from nano- to microdimensional scales.