This PDF file contains the front matter associated with SPIE Proceedings Volume 11673, including the Title Page, Copyright information, and Table of Contents.

Several conditions—including optics, work material and the environment—can influence the results of laser processing. The physical model of laser-processing phenomena is represented as a complex function; thus, the development of a prediction model using machine learning (ML) may be an effective approach. In this study, the quantity of ablation under femtosecond ultrashort pulse laser processing was predicted using an ML model. For work materials, polycrystalline diamond was used as a composite material, cold rolled steel and aluminum were used as metals, silicon was used as a semiconductor and glass was used as an insulator. A total of 340 datasets were prepared for each material. The neuralnetwork algorithm was used to develop the prediction model. We also explored the challenges from the viewpoint of materials informatics. By applying the algorithm to each material dataset, prediction models with ±20 % precision were developed. When the algorithm was applied to all material datasets, the resulting prediction models had ±40 % precision for the single materials, whereas the prediction function was far from ideal in the case of the composite material. It is necessary to tune the input datasets (particularly the physical conditions of the composite material) for the ML model.

Bessel and annular laser beams offer intriguing possibilities for material processing. However, current beam shaping methods can be limited in tunability, speed, or parallelization possibilities. Here, we show how ultrasounds in liquids enable generating user-selectable arrays of Gaussian, Bessel-like, or annular beams. By cascading two liquid-filled acoustic cavities, each with a different geometry, light control can be achieved at microsecond time scales. Such an acousto-optic technology is easy to implement in current laser-direct writing workstations, providing an unprecedented ability to tune light fields based on application.

In this study, we developed a liquid-crystal spatial light modulator with high laser power capacity for industrial ultrafast pulse lasers to demonstrate innovative manufacturing and fabrication techniques using a cyber-physical system. The incident phase performance characteristic of this device was obtained with a 60 W, 1035 nm ultrafast laser. This research work will help to accelerate the use of liquid crystal spatial light modulators for high-precision laser processing of resistant materials and high-throughput for additive manufacturing.

The crystallization of a-Si leads to alterations in the morphology of Si film such as surface color and surface roughness as a result of excimer laser annealing (ELA). These surface changes correlate with the characteristics of polysilicon films. The quality of crystallized poly Si has been evaluated by Non-destructive optical inspection methods. This study aims to use deep learning to estimate the quantitative relationship between the microscope images of a low-temperature polycrystalline silicon (LTPS) film and the mobility of an LTPS thin film transistor (TFT). This method would make it possible to measure the mobility from the images captured after annealing and improve the crystallization by in situ feedback. An a-Si substrate with a film thickness of 100 nm was polycrystallized by employing a KrF (wavelength of 248 nm) excimer laser, after which an optical microscope image of the substrate was captured. By changing the laser fluence and the number of shots (44 conditions N=10), LTPS films of various surface morphology were fabricated. We fabricated 440 transistors using these LTPS channels (channel size L = 20 μm, W = 30 μm) and measured their mobilities. Then, we performed deep learning with these sets of annealed optical microscope images and the corresponding mobilities. The mobility was estimated with an accuracy of ±12.8 cm² V^-1 s^-1. Further improvement of the prediction accuracy (<±5 %) is needed for in-situ feedback. We plan to increase the number of images and use transfer learning to improve prediction accuracy.

Over the last decade industrial ultrafast lasers with pulse durations between 300 fs and 10 ps, average output powers of up to 150 W and single pulse energies in the range of 10 to 250 μJ have been deployed in various industrial applications that require microscopic material removal within small areas with minimum heat affected zones. This paper will provide a detailed understanding of the influence of laser wavelength, pulse duration, pulse fluence and the temporal distribution of the laser pulses (i.e. seeder burst mode operation) on the speed and quality of the machining process. Experimental data for more than 25 materials commonly used in micro-machining applications have led to guidelines for optimizing ultrafast laser machining processes. A review of the industrial ultrafast laser market and a discussion of the main applications are also provided.

Femtosecond laser (Pharos, Light Conversion) with the possibility to produce bi-burst pulses with a repetition rate of 64.5 MHz or/and 4.88 GHz was used to structure copper and steel samples. Ablation efficiency and quality were studied by varying number of pulses per burst in conventional burst regimes and in the bi-burst mode. The comparison of burst, bi-burst and single-pulse ablation efficiencies was done for beam-size-optimised regimes, showing the real advantages and disadvantages of milling and drilling processing approaches.

Within the last decade, ultrafast laser micromachining has found broad applications in a variety of scientific and industrial fields. Likewise, green technologies like E-mobility, photovoltaics or wind power plants have become essential in helping to protect our environment within the last years. Such advancements as well as improvements concerning other electronic devices are profiting from a continuous progress in semiconductor development. Hereby, among other wide-gap semiconductors, SiC is a key material for the production of many high power electronic devices due to its beneficial material properties. Compared to Si-based devices, electronic elements based on SiC enable higher voltages or an increase of general device efficiency. Since well-established production technologies for Si are often not directly transferrable to the machining of SiC, efficient and productive laser-based micromachining calls for extensive parameter studies prior to volume production. In this contribution, we show a comparison of ultra-short pulsed Si- and SiC-machining, as well as different benefits of highly flexible laser systems like the TruMicro series 2000. Choosing an optimized temporal energy deposition on a short- to ultra-short timescale can address a variety of machining aspects like ablation efficiency and surface quality. Using the unique features of the TruMicro series 2000, the temporal energy deposition can be influenced during operation on a femto- up to a microsecond timescale by tuning parameters such as the ultrashort pulse duration or employing bursts in the MHz- and GHz-regime. This enhanced flexibility leads to comprehensive and automated parameter studies that allow for next-generation process understanding.

Ultrashort pulsed lasers are becoming used in multiple applications thanks to their extremely short pulse durations, which confine processing within the irradiated zone and ensure a precise material ablation. However, ultrashort pulsed lasers encounter some challenges at high-speed material removal. In this situation, the use of higher power lasers for increasing ablation rates leads to detrimental effects due to heat accumulation. Recently, GHz burst mode laser ablation has been proposed as a method to overcome this limitation by applying ablation cooling. Following this approach, we study the influence of laser irradiation parameters in burst mode on the ablation efficiency and surface microfabrication quality with special interest in the use of different wavelengths, since most studies are often limited to use the fundamental wavelength in the near infrared. Bursts of pulses used in this study contain multiple pulses happening at an ultrafast ultrafast repetition rate of 5 GHz.

We investigated GHz pulse bursts ablation on metals, silicon, zirconium dioxide, soda-lime glass and sapphire for surface structuring applications with a commercial laser system providing a burst pulse frequency of 5.4 GHz and a maximum of 25 pulses per burst pulse train. The results on metal show dramatic decrease of the ablation efficiency and a reduction of the machining quality. For silicon we also observed a reduction of the ablation efficiency for GHz pulse bursts but found a strong increase for MHz pulse bursts using a 10 ps laser system. On glass an increase of the ablation rate for GHz pulse bursts was observed, however with pure machining quality indicated by crakes in the surface and boarders. Zirconium oxide was the only investigated material, where a GHz pulse bursts induces a moderate higher ablation efficiency with comparable surface qualities, however a 10% higher ablation rate was obtained with a 10 ps laser system.

Optical elements are usually fabricated via conventional well-established processes - milling, grinding and polishing. However, these techniques cannot fully satisfy the growing demand for miniaturized optics with tailored properties. An alternative technology is a laser-based fabrication, including the ultrashort laser ablation and the subsequent CO₂ laser polishing steps. Although this technique allows complex surface structuring, the fabricated optics require validation. In this contribution, we present the characterization of the laser-fabricated axicon from fused silica and comparison with the conventional element. We demonstrate that laser-fabricated axicon can generate the high-quality optical Bessel beam with a long non-diffractive length, which could be applied for 1 mm-thick glass intra-volume dicing. Furthermore, we demonstrate that the astigmatic aberrations, introduced via axicon tilt operation, allow generation of the asymmetrical intensity pattern, which could enhance the cleavability of modified glass sheets. The scribing process was optimized by the variation of processing parameters to minimize the force, required to separate modified glass sheets, using the fourpoint bending setup. Furthermore, the quality of the generated beam and volumetric scribing performance was compared to the conventional commercial oblate-tip axicon.

In this study, we are developing the process of glass ablation by 248nm excimer to make micro-via to the glass material. The interposer connects many pins between both sides electrically. Therefore, the micro-via to the glass substrate must be needed.　However, the micro-via machining to the glass material is difficult because the glass is brittle material. We report microdrilling processability of less than 20um diameter for glass material using a 248nm excimer laser. We also report the investigation result of the dependence of the drilling rate and laser fluence and laser pulse width.

In this work, we will introduce the Bessel beam asymmetry control for glass dicing applications. Asymmetrical Bessel beam can be used to form modifications inside the glass with dominant crack propagation direction optimizing the dicing speed and sample separation forces. The Bessel beam asymmetry control will be demonstrated by applying axicon tilt operations and other approaches including the beam shaping with amplitude masks. Further, the Bessel beam dicing process will be compared to conventional processing techniques such as mechanical dicing (score and brake method), diamond saw and water jet cutting.

Pancharatnam-Berry phase enables various flat special optical elements such as top-hat converters. We present a study on engineering efficient vectorial top-hat converters inscribed in the glass by high-power femtosecond laser pulses. We start with a phase-encoded top-hat converter and demonstrate how its efficiency can be further increased by adjustment of phase masks and various parameters. We use self-organized nanogratings inscribed by a femtosecond laser for the creation of the converter (produced by 'Workshop of Photonics'). Experimental verification of the concept is also presented.

Glass-to-glass welding using ultrashort pulse laser is attracting attention. However, the low processing speed and the requirement of the small air gap between glass substrates have impeded its use in industry. In our study, we achieved rapid welding of glass substrates by coaxially focusing a single femtosecond laser pulse and a continuous-wave (CW) laser with a wavelength that transmits through glass. The selective absorption of the CW laser into the excited electrons increased the processing speed by a factor of 500 compared to the conventional method, while the allowable gap increased by a factor of 4.

We report on our recent developments in the field of ultrashort pulse welding of transparent and transparent to opaque materials. Based on recent trends in diverse branches such as biomedicine or consumer electronics we obtain a demand of reliable and sustainable joining technologies. This can be addressed by the adhesive free and localized laser joining technique using ultrashort laser pulses. Nonlinear absorption as well as heat accumulation within the focal region generate localized joints that are long term stable. On the other hand, the short focal tolerance and small gap size that can be bridged leads to high requirements for the surface quality of the weld partners hindering a cost-effective industrial usage. To overcome these limitations, spatial and temporal beam shaping of the ultrashort laser pulses is used. Based on temporal energy modulation together with the world´s first optics for ultrashort pulse welding (Top Weld optics) much better weld performance in terms of focal tolerance and gap bridging is achieved. The process allows for the bridging of gaps up to 10μm and a focal tolerance of up to 300μm which is several times higher compared with Gaussian focusing (4μm gap size, 80μm focal tolerance). This enables a highly reproduceable welding process even for larger sample dimensions e.g. in the field of architecture. Furthermore, to ensure welding in industrial environment with high throughput a simple process diagnostic based on monitoring the process illumination is presented.

We present a picosecond-laser-based modification process within the bulk of silicon at 2-µm wavelength. For optimizing the process to reliably generate defined modifications, different pulse durations in the span from femtoseconds to picoseconds and different focusing conditions at different depths in silicon were investigated. A predetermined cleavage plane was realized by transversal scanning. The force required to break the sample at the desired position was analyzed for the different processing conditions. Overall our results constitute the basis for picosecond-laser-based dicing of silicon.

We present a dynamic pulse propagation modelling and experiments for femtosecond laser bonding of glass to glass/metal. The modelling provides quantitative estimates of the heat affected zone and weld geometry, incorporating the nonlinear electron dynamics along with temperature-dependent thermal properties. The model numerically determines the desired relative position between the geometrical focus of a femtosecond-laser-pulse and the interface of the two substrates to be welded, for the first time to our knowledge. The welding results of two similar and/or dissimilar materials using the model-predicted weld geometry and offset distance will be presented. This research was supported by NASA SBIR contract 80NSSC20C0432.

[100], [110] and [111] oriented silicon shows different behavior when it is machined with 10 ps pulses in the NIR. For the [100] orientation the roughness increases to 2.8 µm when the peak fluence is raised to 1.6 J/cm2 then drops down to a value below 200 nm for a fluence of 2 J/cm2 and stays below 300nm for fluences up to 7.5 J/cm2. For the other orientations a completely different behavior is observed. The roughness constantly increases to 900 nm at 1.6 J/cm2 and then further to about 8 µm for a peak fluence of 7.5 J/cm2.

We have discovered that the pre-irradiation of a below-ablation-threshold femtosecond laser pulse (first pulse) suppressed titanium ablation rate by subsequent irradiation of another above-ablation-threshold femtosecond laser pulse (second pulse). To ablate titanium targets, we used linearly polarized femtosecond laser pulses (810nm wavelength, 45fs pulse duration, 10Hz repetition rate). Ablation suppression was transiently observed with the delay of several hundreds of picosecond. With these delays, the ablation rate with 10% below-ablation-threshold first-pulse pre-irradiation was suppressed to half of that without pre-irradiation. This result indicated that the below-ablation-threshold first-pulse preirradiation does not ablate the titanium target but changes the optical property of the surface. To understand the physics of the ablation suppression, we have developed and performed a new measurement to estimate the temporal changes of the effective laser penetration length (LPL) induced by the below-ablation-threshold first-pulse pre-irradiation. We developed a new description of the dependence of the ablation rate on the laser fluences and delay by considering the absorption and decay of the laser pulse energy in the target. We have demonstrated that below-ablation-threshold firstpulse pre-irradiation reduced LPL with the delay of several hundreds of picosecond. The result indicated that the preirradiation of a below-ablation-threshold first-pulse changed the titanium surface into a novel state with reduced LPL, which is not explained by simple heating of surface.

We report that few-cycle laser pulses at low fluence can produce sub-100 nm periodic nanostructures on DLC surfaces through nanoablation induced by short-range surface plasmon polaritons (SR-SPPs). The 7-fs and 100-fs laser pulses from Ti:sapphire lasers were used. The period of the nanostructures with 7-fs pulses was much smaller than those with 100-fs pulses. The Raman spectrum showed that the modified layer in a DLC surface irradiated with 7-fs pulses was thinner than that with 100-fs. By using a model target, the period calculated for the excitation of SR-SPPs was in good agreement with that in the experiments.

Rate of the photoionization is the key quantity employed in all simulations of nonlinear absorption and generation of free carrier associated with high-intensity interactions of ultrashort laser pulses with transparent solids. The rate is evaluated by either numerical methods or by analytical models. However, they meet significant challenges when applied to the pulses carrying from 3 to 20 cycles because of the single-frequency approximation underlying the analytical models and the difficulties met by the numerical methods in modeling of parametric scaling of the rate. Here, we report an analytical timedomain model of the photoionization that fits that range of the pulse width. Analytical relations for the photoionization rate are derived in the form of asymptotic series. The zero-order term of the series is the Keldysh-type rate evaluated at central frequency of pulse spectrum. Higher-order terms describe departures from the single-frequency approximation of the Keldysh-type models and accurately evaluate the photoionization rate by the pulses carrying 3 or more cycles. Significant influence of carrier-envelope phase in magnitude of the photoionization rate is reported. Substantial departure from the Keldysh-type monochromatic models of the photoionization is demonstrated and discussed. The reported model may serve as a highly effective simulation tool for modeling of nonlinear interactions of high-intensity few-cycle laser pulses with transparent solids.

Surfaces inspired by nature and their replication find great interest in science, technology, and medicine due to their unique functional properties. This research aimed to develop an efficient laser milling technology using single-pulse- and burst-modes of irradiation to replicate bio-inspired structures over large areas at high speed. The ability to form the trapezoidal-riblets inspired by shark skin at high production speeds while maintaining the lowest possible surface roughness was demonstrated.

LIPSS as well as hierarchical structures were generated by applying picosecond laser irradiation on a stainless steel-304 probe in a confinement liquid medium. Periodicity modification from high to low spatial surface frequency LIPSS was observed by modifying the pulse repetition rate from 1.3 to 402 kHz at a constant fluence. One of the outcomes reported in this study was the wettability analysis of the processed area which yielded significative changes on the contact angle between a water drop and the treated surface showing a wetting transition from hydrophilicity to hydrophobicity as an effect of the multiple impact pulses.

It is known that the several-times irradiation of a short pulse laser with fluence near the ablation threshold on material induces self-organization of fine periodic surface structures (so called LIPSS: laser induced periodic surface structure) with periodic interspaces Ʌ smaller than the laser wavelength ʎ. In particular, LIPSS such as Ʌ ≪ ʎ are called “fine LIPSS”. And they are attracting much attention as a method of processing for structures finer than the diffraction limit of laser light. However, their formation mechanism has not been clarified yet. To clarify the formation mechanism of LIPSS, in-situ observation is an effective way. However, the measurement of the small periodic interspaces with fast time scale (comparable to the laser pulse duration) are the difficulties. On a way to in-situ observation, we have reported the LIPSS formation on semiconductors irradiated by mid-infrared Free-Electron Laser (MIR-FEL). Their periodic interspaces are several micrometers and therefore can be measured by visible light. In this presentation, we compared the features of LIPSSs by MIR-FEL to the several models applied to LIPSSs by near-infrared or visible light lasers. Through this discussion, we estimated the temporal resolution needed for in-situ observation.

Micro/nanoscale surface patterning of zirconia ceramic is needed for surface functionalization and performance enhancement, such as improved biocompatibility of medical devices, as well as device miniaturization. Therefore, formation of laser-induced periodic surface structures (LIPSS) with periods shorter than the laser wavelength on a zirconia ceramic was carried out using an ultrashort pulsed laser. In this case, it is important to shorten the processing time required for forming the LIPSS without deteriorating the processing quality. Using the various-parameters-controlled laser processing and observation system, we optimized LIPSS formation by changing parameters such as pulse duration, repetition frequency, number of shots, and fluence.

We present our latest progresses on the development of integrated photonic devices as well as microfluidic chips of unprecedented characteristics and performances using femtosecond laser micromachining. We demonstrate ultra-high Q microresonators in lithium niobate on insulator (LNOI), on-chip micro-laser and waveguide amplifier, and high-throughput micro-chemical reactor. The achievements are the result of persistent effort on improving the precision and efficiency in ultrafast laser processing.

Currently the most widely used technique for solder paste deposition is Surface Mount Technology (SMT), which involves the printing of solder paste using a stencil, onto printed circuit board (PCB) interconnection pads. However, this process accounts for 50-70% of post-assembly defects. Here, we report the use of Laser Induced Forward Transfer (LIFT), for the reliable printing of commercially available solder pastes. LIFT is an environmentally friendly, mask-less technique and offers high resolution (down to 60 μm) control over the printed volume with high throughput. LIFT has been previously employed for the reproducible and high throughput (speed up to 2 m/s) printing of metal nanoparticle inks, but the achievement of reproducible deposition of bumps comprising micro-particles (such as in type-5 or 6 solder pastes) stills poses severe challenges. By investigating the whole spectrum of LIFT process parameters – the donor film thickness, the donor – receiver gap, the effect of a sacrificial layer, the laser spot size and shape and the laser fluence - this paper reports on the digital and reproducible transfer of solder paste bumps at the designated pads of ultra-fine pitch PCBs. The process optimization is enabled by employing a side view set-up, consisting of a high-speed camera (up to 540 kfps) coupled with a lens system for 3x optical magnification of the ejection. The reported results highlight the advantages of a digital and high-resolution solder paste deposition method and validate the compatibility of LIFT with PCB assembly.

An organic build-up film is used as the substrate material for a semiconductor multi-die package. However, the miniaturization of the organic build-up film process by the commonly used 355 nm UV laser has almost reached the limit due to its long wavelength. Therefore, to miniaturize the build-up film process, it is necessary to use an excimer laser with a shorter wavelength than the UV laser. In addition, the high photon energy due to the short wavelength of the excimer laser means the thermal effect of the material can be reduced by direct photon absorption. We have developed several types of DUV excimer lasers. One of them is a high power 248 nm excimer laser with free spectrum operation. The 248 nm excimer laser can be applied to the process of organic materials for semiconductor packages. We are developing the processing of organic materials by 248 nm excimer laser. The organic materials are processed directly by the irradiation using the mask by 248 nm excimer laser. We report microdrilling processability of less than 20 μm diameter for a build-up film using a 248 nm excimer laser. The dependence of the taper angle, processing rate on the fluence for various via hole diameters was evaluated for major commercial build-up films. The results of this study indicate the appropriate selection of build-up film material and excimer laser processing fluence to achieve the processing target diameter and taper angle.

The selective surface activation induced by laser (SSAIL) for electroless copper deposition on PC-ABS blend is one of promoising technique of electric circuit formation on free-form dielectric surfaces, which broadens capabilities of 3D microscopic integrated devices (3D-MID). The process consists of laser excitation, chemical activation of laser-excited areas by dipping in a liquid and electroless copper deposition of laser-treated areas. The limiting factor to increase throughput of the technology is a laser activation step. Laser writing is performed by modern galvanometric scanners which reach the scanning speed of several meters per second. However, adverse thermal effects on PC-ABS polymer surface abridge the high-speed laser writing. In this work, an advantageous laser beam scanning technique by shifted pulse is used to overcome mentioned problems.

The surface of native polydimethylsiloxane (PDMS) was modified into black structures by irradiation of femtosecond laser pulses. Material analysis conducted on the modified areas revealed the formation of silicon carbide (SiC) nanocrystals, as well as multilayer graphitic carbon. Furthermore, electrical conductivity measurements of structures fabricated using various fabrication parameters, suggest that the amount of defect in the formed graphitic carbon affects the electrical conductivity of the fabricated structures. A preliminary demonstration of strain sensing was performed using the structures fabricated, indicating the potential of the structures fabricated by the femtosecond-laser-based modification of PDMS for flexible device applications.

In recent years, polycarbonate (=PC) is gathering attention as a light and strong material for smart windows. In the presentation, a patterning method of Al deposited film on silicone hard-coated polycarbonate by 157 nm F2 laser irradiation will be reported. A photomask placed on Al thin film and irradiated by F2 laser and the non-irradiated area was removed by KOH aq. The mechanism of the patterning will be discussed based on XPS, AFM, and ATR-FTIR measurement.

We demonstrate the microfabrication of double-network (DN) hydrogels by multi-photon polymerization induced by focused femtosecond laser pulses. Two different poly (ethylene glycol) diacrylate (PEGDA) solutions (Mw=700 and 4000) were cured as both structures were crossing each other, allowing overlapped structure to form double networks composed of both employed polymer chains. This method allows the spatially-selective microfabrication of DN hydrogels inside the microfabricated hydrogel structures, which would realize the hydrogel microstructures showing spatially varied distribution of strength and stiffness.

Laser-Induced Forward Transfer (LIFT) is a direct-write laser technique for the transference of material in an enormous range of viscosities and rheological behaviors, from solid-state to low-density inks. Furthermore, LIFT enables the transference of small volumes of material (as low as picoliters) with a high lateral spatial resolution (down to a few micrometers) to produce printed patterns with great flexibility. In this work, simulations using a finite-element model involving Phase Field tracking method are presented and compared with experimental results. Specifically, two LIFT processes are studied: a modified model is used to reproduce the secondary effects (such as bulgy shapes and secondary jets) observed after several ms in Blister-Actuated LIFT (BA-LIFT) of glycerol/water mixtures, and a model for LIFT transference of high-viscosity metallic pastes employed to study the different regimes observed in experiments (non-transference, explosive, cluster, dot, and bridge transfer)

In this work transmission and reflection losses in silicon diffractive THz optical components fabricated by direct laser ablation are investigated. One of the possible sources of reflection/transmission losses in laser-fabricated optics is scattering due to the roughness of laser formed surface. Therefore, influence of laser processing parameters on the transmittance of laser processed silicon wafers was investigated in 0.1 –4.7 THz range. Transmittances of silicon samples ablated in ambient air and argon atmospheres were also compared. Using laser ablation technology MPFLs for 0.6 and 4.7 THz frequency radiation were fabricated and their performance was evaluated.

We report direct laser writing of graded-index optical waveguides via phase segregation in initially homogenous silicongermanium (SiGe) thin films epitaxially-grown on silicon substrates. We used a continuous wave (CW) laser operating at a wavelength of 532 nm. The laser beam was focused to a 5 μm diameter spot on the surface of SiGe films with a thickness of 575 nm and a Ge concentration of %50. Compositional separation of a SiGe film was induced by melting the surface, and the composition profile was tailored by controlling the scan speed of the laser-induced molten zone in a range of 0.1-200 mm/s. At high scan speeds, scanning the laser beam produces a travelling Ge-rich molten zone, where a build-up of Ge content occurs at the trailing edge because of insufficient diffusion-limited Ge transport. Material characterizations have revealed that the laser-processed SiGe microstripes consist of Ge-rich strip cores (> 70% Ge) surrounded by Si-rich under-claddings (<30% Ge). Scan-speed dependent phase segregation allows for fabrication of graded-index SiGe waveguides with tunable compositional profiles, which were characterized by optical transmission measurements, and modal analysis using simulations. Our method could also be applied to pseudo-binary alloys of ternary semiconductors (AlGaAs), which have equilibrium phase diagrams similar to that of SiGe alloys.

In this study, we demonstrate that the P3 scribing of CIGS cells with nanosecond pulses can compete with ultrashort picosecond pulses producing very low conductivity isolation scribes. The investigation covered a wide range of laser wavelengths – from 355 nm to 2.5 µm. Additionally, P3 processing with extremely high speeds (up to 25 m/s) was investigated in CIGS cells. Results showed that heat accumulation effects occurred even in low-pulse-overlap removal of TCO layers (lift-off). Furthermore, processing at highest speeds demonstrated the deteriorated quality of P3 scribes due to ejected TCO flakes partially shielding the laser beam. Nevertheless, scribe conductivity remained low.

The commercially available Synova Laser MicroJet® technology combines conventional laser capabilities with compressed water jet that precisely guide laser beam in a similar manner to optical fibers. Due to physical water breakdown, technology is typically focused on the nanosecond pulse duration range. A stable beam shaping setup with a diffusor and commercial fiber to couple into water jet, was developed allowing to test Laser MicroJet® at 100-300 ps pulse duration. The change to energy intensity profile with diffuser allowed to triple coupled energy without inducing the physical breakdown in water and could be further increased by implementing 2 and 3 pulse bursts into the setup. High quality scribing was achieved at Si wafer at high scanning speed. Preliminary results on multilayer Si-wafer have demonstrated that scribing quality is in this case more feedrate dependent, limited chipping occurring at speed of commercial interest. Cutting tests were performed on semiconductors as well as on metals. On both, it was possible to achieve high quality cuts with high feedrate up to 12 mm/s with Ra < 0,3 μm.

Silicon nanoparticles suspended in deionized water were obtained by the laser ablation of solids in liquids technique. A silicon wafer target was ablated with a Nd:YVO4 pico-second laser emitting at 1064 nm with 10 ps pulse width at a repetition rate of 402 kHz with an energy per pulse of 106 µJ. The effect of fluence changes in nanoparticle size and optical properties was studied. The fluence was varied from 2 to 6 J/cm2 by attenuating the beam by means of optical attenuators. Results show a strong relation between nanoparticles size and fluence values. Optical characterization gives bad gap values higher than that of bulk Si, indicating the existence of quantum confinement effects produced by size reduction of Si nanocrystals.

Many materials with wide bandgap, such as glasses, sapphire, and silicon carbide (SiC), have excellent optical, electrical, and mechanical properties and are used in various industrial and scientific applications. Ultrashort pulse laser processing has been attracting attention as a method of micromachining wide-bandgap materials. Because the peak intensity of ultrashort pulse laser is extremely high, its focused pulse can make wide-bandgap materials absorb its light energy via multiphoton absorption. However, it has a problem that damage occurs around the processed region. In this study, we observe the high-speed phenomena during the ultrashort pulse laser drilling of wide-bandgap materials using pump-probe imaging in combination with a high-speed camera to clarify the mechanism of damage generation. This method visualizes both the static phenomena such as the processed shape and the damage, and the dynamic phenomena such as the electron excitation and the stress wave propagation, which change with each pulse irradiation. In addition, we conduct the experiments by changing the pulse width and the material to be processed to investigate the dependence of damage generation on the processing condition. The results show that stress waves propagating inside the material during processing cause the damage, and that the damage generation pattern changes depending on the pulse width and material. This study contributes to optimizing the processing conditions to suppress the damage during the ultrashort pulse laser processing of wide-bandgap materials.

Stainless-steel type 316L (SS316L) plate was fabricated by selectively laser melting method (SLM) in vacuum. SS316L has excellent properties such as a high corrosion resistance and hardness, but fabricating complicated structures is challenging due to difficulties in processing the material. Although SLM can fabricate complicated shapes because it builds a 3D material layer-by-layer from a powder, some issues have yet to be resolved. One is that spatter is generated by metal powder scattering during laser irradiation. Another one is the denudation zone due to the balling effect. Spatter is considered to be dominated by the recoil pressure of fume caused by melting and evaporation of metal, and it is not possible to suppress the expansion of fume and reduce spattering by changing the atmospheric pressure. In addition, it is considered that the balling effect is dominated by the surface tension of the molten land under atmospheric pressure with a lot of convection. Therefore, in this study, SS316L plate was fabricated by changing the atmospheric pressure in the chamber, and the effect of atmospheric pressure on the spattering and balling effects was clarified. First, SS316L powder was set in a vacuum chamber, depressurized using a vacuum pump, and then irradiated with a single-mode fiber laser. Spatter was captured using a high-speed video camera during laser irradiation of SS316L powder. After that, polishing, edging, and cross-section observation were performed. As a result, it was found that when the atmospheric pressure was lowered, the spatter amount and bead the height decreased, and the denudation zone increased.

A hybrid laser system which combines preheating with a blue diode laser with welding with a single mode fiber laser was developed to realize a highly efficient laser welding of copper. With the hybrid laser system, the blue diode laser and the single mode fiber laser were combined coaxially and a stair shape beam profile was formed at the processing point. Each laser was irradiated to a copper sample and the output power of the blue diode laser was varied to investigate an effect of preheating with it on the welding with the single mode fiber laser. The melting and solidification dynamics of copper was evaluated with a high speed video camera and a thermo camera. As the results, it was found that the melting volume of copper and the temperature at the processing point increased by preheating with the blue diode laser. The copper wire with 2.0×3.5×50 mm was weld in 0.3sec by using hybrid laser with 1kW single mode fiber laser and 200W blue diode laser. Thus, it was concluded that a highly efficient welding of copper was achieved with the preheating with the blue diode laser.