This PDF file contains the front matter associated with SPIE Proceedings Volume 10091, including the Title Page, Copyright information, Table of Contents, Introduction (if any), and Conference Committee listing.

Vanadium dioxide (VO₂) undergoes a metal-insulator transition (MIT) at 68°C, at which point its electrical conductivity changes by several orders of magnitude. This extremely fast transition (Δt < 100 fs) can be induced thermally, mechanically, electrically, or optically. The combination of fast switching times and response to a broad range of external stimuli make VO₂ an ideal material for a variety of novel devices and sensors. While the MIT in VO₂ has been exploited for a variety of microwave/terahertz applications (i.e. tunable filters and modulators), very few devices exploiting the fast switching time of VO₂ have been reported. The electrical properties of thin film VO₂ (conductivity, carrier concentration, switching speed, etc.) are highly dependent on growth and post-processing conditions. The optimization of these conditions is therefore critical to the design and fabrication of VO₂ devices. This paper will report the effects of various pulsed laser deposition (PLD) growth conditions on the metal-insulator transition in thin film VO₂. In particular, we report the effect of PLD growth conditions on the stress/strain state of the VO₂ layer, and the subsequent change in electrical properties. Finally, results from fabricated VO₂ devices (THz emitters and THz modulators) will be presented.

In this work, the experimental results of the graphite oxide (GO) reduction with laser irradiation are presented. GO films on a flexible polycarbonate substrate were produced using a modified Hummers method. Experiments were conducted using a picosecond laser. The pulse energy and beam scanning speed were varied during the reduction experiments. All experiments were performed in air. Raman spectroscopy measurements and electrical resistance measurements were implemented on the laser treated GO samples. Scanning electron microscopy (SEM) was used for morphology inspection. Experiments results showed that for certain range of laser microfabrication parameters, electrical properties, suitable for electronics applications can be achieved in reduced GO films. Such laser-modified GO films are intended to be used as contacts for flexible supercapacitors.

In this study, silicon nitride film is deposited by laser assisted chemical vapor deposition technique based on the direct photolysis of SiH₄/NH₃ gas mixture using argon fluoride excimer laser of 193 nm wavelength at low substrate temperature around 100°C. By illuminating laser beam in parallel to sample surface, sample damage or heating can be avoided allowing compatibility of temperature sensitive device architectures. A wide range of processing parameters for laser and reactant gases are examined in correlation with deposition mechanisms.

We propose an innovative method for aluminum doping of 4H-SiC with passivation films, induced by XeF excimer laser irradiation in AlCl3 aqueous solution (28.6 wt%). A 100-nm thick Si passivation film was deposited on an n-type 4H-SiC substrate by physical vapor deposition. Using a laser beam (200 μm × 170 μm) with an irradiation fluence of 0.5–5.0 J/cm², 1–300 shots were administered. After laser irradiation of 1.0 J/cm² and 300 shots, an Al-Si-O compound film was formed on the SiC surface. The compound film was removed by chemical wet etching and plasma treatment. After the removal of the compound film, no irradiation damage was observed on the SiC surface. From the results of secondary ion mass spectrometry measurements, high concentration aluminum doping (about 1 × 10²⁰ /cm³ at the surface) was confirmed. The I-V characteristics of the junction between the n-type substrate and the irradiation area indicated clear rectification with a large on/off ratio of 9 decades in the range of ±10 V. When forward biased, electroluminescence phenomenon with a peak at 387 nm, corresponding to the electroluminescence of SiC’s band gap, was confirmed. These results prove the achievement of Al doping of n-type SiC to p-type using laser irradiation without any damage to the SiC surface.

Light-weighting of vehicle is now strongly required for reducing gasoline consumption and CO₂ emission. In this study, F2 laser was irradiated to the surface of hard silicone resin, coated by dip coating method onto the film of acrylic resin on a polycarbonate substrate. The surface part of the silicone resin was photo-chemically modified into SiO₂. One of two types of aperture mask, 3×3 mm² and 50×50 μm², was set on the sample surface. The single pulse fluence was varied from 4 to 14 mJ/cm², pulse repetition frequency was set to 10 Hz, and irradiation time was changed from 30 to 120 s. N₂ gas was induced around the surface of the sample. After modification, SiO₂ modified layer was etched by HF 1% diluted solution, and the etched depth was measured by a stylus-type surface profilometer. As a result of experiments, stress in the SiO₂ modified layer increased by increasing of F2 laser irradiation time. In case of using aperture mask of 3×3 mm², cracks were generated only on the irradiated area for longer irradiation time than 60 s. It is considered that the tensile stress in the modified layer exceeded the tensile fracture strength of 48 MPa of typical SiO₂. When a mesh mask of 50×50 μm² aperture was used, no crack generated even for a long irradiation of 200 s. We found, the tensile stress in SiO₂ modified film can be reduced remarkably with using smaller aperture size of mesh mask, and it is very effective to prevent cracking.

Four-waves mixing (FWM) of co-propagating femtosecond laser pulses is widely used in various practical applications for diagnostic of a medium, for example. Using the problem invariants (conservation laws for four wave pulses interaction) it is possible to develop an analytical solution of the problem under consideration in the frame-work of plane wave approximation and long pulse duration approximation (point–wise model). This solution demonstrates an existence of various FWM modes under their co-propagation. Among them, there is a mode of wave propagation without unchanging intensities. In the case of pulse propagation with inhomogeneous beam profile, this mode results in occurrence of (or oscillating) spatial-temporal domain of unchangeable intensity during certain propagation distance, which depends on SOD (second order dispersion) and beam diffraction. Both these factors destroy this propagation mode. Nevertheless, a pulse with hyperbolic cosine shape may exhibit such propertty. We investigate an influence of a pulse shape as well as a beam profile.

Ultrafast waveguide fabrication has been an active research area since its demonstration, leading to numerous applications. Recently reported high quality waveguide in Gorilla Glass has promoted it as a good candidate for optical devices. In this study, 120-fs laser pulses centered at 520, 650 and 775 nm at a repetition rate of 1 kHz were applied to investigate the influence of the wavelength on micromachining. Grooves ablated onto Gorilla Glass surface with different pulse energies and scanning speeds presented similar features and threshold pulse energy, regardless the excitation wavelength. Fifteen millimeter long waveguides were produced 100 μm below sample surface with pulse energy varying from 250 nJ up to 5 μJ (scanning speed of 200 μm/s). Waveguides longitudinal and transversal profiles were analyzed via optical microscopy and its guiding properties characterized in an objective-lens based coupling system at 633 and 775 nm. Guide modes intensity distribution show that for waveguides fabricated with higher pulse energy light is guided further from the core, while for lower fabrication energy light is guided closer to the center in a more fundamental mode. Considering that light traveling through 15 mm of material in confined mode, we coupled 775 nm fs-pulses into fabricated waveguides. By monitoring the spectrum of the guided light as input pulse energy increased, spectral broadening assigned to self-phase modulation effects was observed followed by white-light generation starting at 450 nm. In conclusion, we found that micromachining on Gorilla Glass is wavelength independent and inscribed waveguides present desirable nonlinear features.

Polydimethylsiloxane (PDMS) is a material used for cell culture substrates / bio-chips and micro total analysis systems / lab-on-chips due to its flexibility, chemical / thermo-dynamic stability, bio-compatibility, transparency and moldability. For further development, it is inevitable to develop a technique to fabricate precise three dimensional structures on micrometer-scale at high aspect ratio. In the previous works, we reported a technique for high-quality micromachining of PDMS without chemical modification, by means of photo direct machining using laser plasma EUV sources. In the present work, we have investigated fabrication of through holes. The EUV radiations around 10 nm were generated by irradiation of Ta targets with Nd:YAG laser light (10 ns, 500 mJ/pulse). The generated EUV radiations were focused using an ellipsoidal mirror. It has a narrower incident angle than those in the previous works in order to form a EUV beam with higher directivity, so that higher aspect structures can be fabricated. The focused EUV beam was incident on PDMS sheets with a thickness of 15 micrometers, through holes in a contact mask placed on top of them. Using a contact mask with holes with a diameter of three micrometers, complete through holes with a diameter of two micrometers are fabricated in the PDMS sheet. Using a contact mask with two micrometer holes, however, ablation holes almost reaches to the back side of the PDMS sheet. The fabricated structures can be explained in terms of geometrical optics. Thus, we have developed a technique for micromachining of PDMS sheets at high aspect ratios.

Being lightweight materials with good mechanical and thermal properties, hollow glass micro-particles (HGMPs) have been widely studied for multiple applications. In this study, it is shown that by using reduced binder fraction diluted in solvent, enables minimal contacts among the HGMPs assisted by a natural capillary trend, as confirmed by optical and electron microscope imaging. Such material architecture fabricated in a composite level proves to have enhanced thermal insulation performance through quantitative thermal conductivity measurement. Mechanical strength has also been evaluated in terms of particle-binder bonding by tensile test via in-situ microscope inspection. Effect of laser treatment was examined for further improvement of thermal and mechanical properties by selective binder removal and efficient redistribution of remaining binder components.

The fabricated composite materials have potential applications to building insulation materials for their scalable manufacturing nature, improved thermal insulation performance and reasonable mechanical strength. Further studies are needed to understand mechanical and thermal properties of the resulting composites, and key fabrication mechanisms involved with laser treatment of complex multi-component and multi-phase systems.

A rapid, mask-less deposition technique for the deposition of conductive tracks to nano- and micro-devices has been developed. The process uses a 405 nm wavelength laser diode for the direct deposition of tungsten tracks on silicon substrates via laser assisted chemical vapour deposition. Unlike lithographic processes this technique is single step and does not require chemical masks that may contaminate the substrate. To demonstrate the process, tungsten was deposited from tungsten hexacarbonyl precursors to produce conductive tracks with widths of 1.7-28 μm and heights of 0.05-35 μm at laser scan speeds up to 40 μm/s. The highest volumetric deposition rate achieved is 1×104 μm³/s, three orders of magnitude higher than that of focused ion beam deposition and on par with a 515 nm wavelength argon ion laser previously reported as the laser source. The microstructure and elemental composition of the deposits are comparable to that of largearea chemical vapour deposition methods using the same chemical precursor. The contact resistance and track resistance of the deposits has been measured using the transfer length method to be 205 μΩ cm. The deposition temperature has been estimated at 334 °C from a laser heat transfer model accounting for temperature dependent optical and physical properties of the substrate. The peak temperatures achieved on silicon and other substrates are higher than the thermal dissociation temperature of numerous precursors, indicating that this technique can also be used to deposit other materials such as gold and platinum on various substrates.

Thermoelectric generators (TEGs) are an attractive means to produce electricity, particular from waste heat applications. However, TEGs are almost exclusively manufactured as flat, rigid modules of limited size and shape, and therefore an appropriate mounting for intimate contact of TEGs modules onto arbitrary surfaces represents a significant challenge.

In this study, we introduce laser assisted additive manufacturing method to produce multi-layered thermoelectric generator device directly on flat and non-flat surfaces for waste heat recovery. The laser assisted processing spans from laser scribing of thermal sprayed thin films, curing of dispensed thermoelectric inks and selective laser sintering to functionalize thermoelectric materials.

ZnO nano/microstructures have attracted much attention as building blocks for optoelectronic devices because of their high crystalline quality and unique structures. We have succeeded in synthesizing ZnO microspherical crystals by a simple atmospheric laser ablation method, and demonstrated ultraviolet whispering-gallery-mode lasing from the spheres. In the microsphere synthesis process, molten droplets formed into spherical shapes by surface tension, and crystalized during ejection from the ablation spot. In this study, we observed the generation of ZnO microspheres by high-speed camera. Now we are trying to control and manipulate the microspheres using a vortex beam.

Zone plates with integrated band-pass filters and binary Fresnel lenses designed for the THz spectral range were fabricated by direct laser ablation in metal films and the silicon substrate. Results on the process performance and quality of the products are reviewed. The focusing performance was measured using the THz source that produces the 580 GHz radiation. The beam was directed to the centre of the fabricated optical elements. Zone plates with integrated band-pass filters have shown the double performance in focusing and spectral selection. The dependence of ablation rate and surface roughness on the laser process parameters was thoroughly investigated on the silicon. The depth of the ablated grooves linearly depends on the number of laser scans number with a particular slope for each scanning speed. The process regime with the 125 mm/s scanning speed provided the most precise control over the ablation depth. The topography measurements of the laser fabricated multilevel phase zone plates (Fresnel lenses) with the 10 mm focal length showed good agreement with the calculated topography. The intensity distribution of the focus spots using the laser fabricated 2, 4 and 8 level binary Fresnel lenses showed better focusing performance when more depth levels were applied in the lens production.

With availability of high power ultra short pulsed lasers, one prerequisite towards throughput scaling demanded for industrial ultrafast laser processing was recently achieved. We will present different scaling approaches for ultrafast machining, including raster and vector based concepts. The main attention is on beam shaping for enlarged, tailored processed volume per pulse. Some aspects on vector based machining using beam shaping are discussed. With engraving of steel and full thickness modification of transparent materials, two different approaches for throughput scaling by confined interaction volume, avoiding detrimental heat accumulation, are exemplified. In Contrast, welding of transparent materials based on nonlinear absorption benefits from ultra short pulse processing in heat accumulation regime. Results on in-situ stress birefringence microscopy demonstrate the complex interplay of processing parameters on heat accumulation. With respect to process development, the potential of in-in-situ diagnostics, extended to high power ultrafast lasers and diagnostics allowing for multi-scale resolution in space and time is addressed.

The essential basis for a reliable and target-aimed process control is the understanding of the interaction between the laser beam and the treated material and this was gained by thorough research on the influence of the process input parameters on the interaction sub processes and on the treatment result. The main players conducting this research over the decades have been research facilities and institutes and this research is still in progress. Since the moment when it was possible to achieve the necessary power density to start the process of deep penetration welding, accompanied by a keyhole, there is hope - and need - to measure e.g. the depth of this vapor channel. In the decades in which the technology of deep penetration welding has been used, various approaches have been developed that allow a message about the depth of the keyhole. The aim of this contribution is to show a compact overview on the different approaches to monitor and/or control micro and macro laser welding processes and especially bring out those which successfully have been transferred from laboratory to serial production in the recent past and will in the near future. Further use includes the acquisition of 3D images around the laser process itself, allowing for coaxial integration of pre- and post-process sensors.

For most micromachining applications, the laser focus has to be moved across the workpiece, either by steering the beam or by moving the workpiece. To maximize throughput, this movement should be as fast as possible. However, the required positioning accuracy often limits the obtainable speed. Especially the machining of small and complex features with high precision is constrained by the motion-system’s maximum acceleration, limiting the obtainable moving spot velocity to very low values. In general, processing speed can vary widely within the same processing job. To obtain optimum quality at maximum throughput, ideally the pulse energy and the pulse-to-pulse pitch on the workpiece are kept constant. This is only possible if laser-pulses can be randomly triggered, synchronized to the current spot velocity. For ultrafast lasers this is not easily possible, as by design they are usually operated at a fixed pulse repetition rate. The pulse frequency can only be changed by dividing down with integer numbers which leads to a rather coarse frequency grid, especially when applied close to the maximum used operating frequency.

This work reports on a new technique allowing random triggering of an ultrafast laser. The resulting timing uncertainty is less than ±25ns, which is negligible for real-world applications, energy stability is <2% rms.

The technique allows using acceleration-ramps of the implemented motion system instead of applying additional override moves or skywriting techniques. This can reduce the processing time by up to 40%.

Results of applying this technique to different processing geometries and strategies will be presented.

To be competitive in industrial applications the throughput is a key factor in laser micro machining using ultra-short pulsed laser systems. Both, ps and fs laser systems are suitable for industrial applications. Therefore one has to choose the right pulse duration for highest ablation efficiency. As shown in earlier publications the efficiency of the ablation process can be described by the specific removal rate, which has a maximum value at an optimum fluence. But its value often bases on a calculation using the threshold fluence and energy penetration depth deduced by measuring the depth of ablated cavities machined with different fluences and number of pulses. But this calculated specific removal rate often differs from the one deduced from ablated squares as recently shown in literature. Further an unexpected drop of the specific removal rate was reported for stainless steel when the pulse duration was reduced from 900 fs to 400 fs. Thus the influence of the pulse duration in the fs and low ps regime onto the specific removal rate is investigated with different methods for industrial relevant materials

Fiber Bragg gratings (FBGs) in the center of multimode microfibers (MM-MF) with 10μm diameter were successfully inscribed with point-by-point method and their reflection spectra show peaks over 10dB signal-to-noise ratio (SNR) and less than 0.5nm bandwidth. FBGs on regular size multimode fiber (~60μm core size) shows nearly continuous reflection spectrum. However, when the diameter of the multimode fiber is reduced to ~10μm, its modal volume significantly decreases so that the remaining optical modes are separated by larger propagation constant difference, resulting distinguishable sharp peaks on FBG reflection spectrum. Therefore, MM-MF based FBGs could be practical sensors for simultaneous multi-parameters with outstanding sensitivity and accuracy.

Femtosecond-pulse modification of the refractive index in transparent materials enables the inscription of fiber Bragg gratings with new features and extended capabilities. In this study we present the results of fiber Bragg gratings inscription in Corning 62.5/125 multimode graded index fiber with IR femtosecond laser pulses. The specifics of point-by-point inscription including single and multiple Bragg grating inscription in limited fiber segment as well as different transverse modes excitation/suppression is discussed. Multimode fiber Bragg gratings inscribed with femtosecond radiation are investigated for the first time directly in the Raman fiber laser cavity.

Nowadays processing of transparent materials, such as glass, quartz, sapphire and others, is a subject of high interest for worldwide industry since these materials are widely used for mass markets such as consumer electronics, flat display panels manufacturing, optoelectronics or watchmaking industry. The key issue is to combine high throughput, low residual stress and good processing quality in order to avoid chipping and any post-processing step such as grinding or polishing. Complimentary to non-ablative techniques used for zero-kerf glass cutting, surface ablation of such materials is interesting for engraving, grooving as well as full ablation cutting. Indeed this technique enables to process complex parts including via or blind, open or closed, straight or small radius of curvature patterns. We report on surface ablation experiments on transparent materials using a high average power (70W) and high repetition rate (1 MHz) femtosecond laser. These experiments have been done at 1030nm and 515nm on different inorganic transparent materials, such as regular and strengthened glass, borosilicate glass or sapphire, in order to underline their different ablation behavior. Despite the heat accumulation that occurs above 100 kHz we have reached a good compromise between throughput and processing quality. The effects of fluence, pulse-to-pulse overlap and number of passes are discussed in terms of etch rate, ablation efficiency, optimum fluence, maximum achievable depth, micro cracks formation and residual stresses. These experimental results will be also compared with numerical calculations obtained owing to a simple engineering model based on the two-temperature description of the ultrafast ablation.

Conventional processing tools of glass cannot fulfil the forever increasing industrial requirements for processing speed and quality. In the future these methods can be replaced by emerging laser-based techniques. While nowadays most of the research is dedicated for thin, especially chemically strengthened glass, used in electronic devices, there is still a need for a suitable processing technique for thick glasses. One of the most material-efficient and energy-efficient glass cutting techniques is to locally weaken the material along the cutting path by generating cracks or material modifications and then separate sheets by applying thermal or mechanical load. Such approach provides a clean cut with an infinitely thin kerf width without a need for post-processing. Bessel-Gaussian beams, commonly generated using a conical lens, have very appealing properties for processing of transparent materials, such as the long non-diffractive propagation length and self-reconstruction. However, due to manufacturing tolerances, the shape of an optical element deviates from an ideal cone and the intensity pattern is non-symmetrical and modulated along the beam propagation axis. We have found that such asymmetry leads to the significant elongation of laser-induced glass cracks along one dominant direction, which can be beneficial for fast glass cutting.

The initial stages of femtosecond laser ablation of gold were observed by single-shot soft X-ray laser interferometer and reflectometer. The ablation front surface and the spallation shell dome structure were observed from the results of the soft X-ray interferogram, reflective image, and shadowgraph. The formation and evolution of soft X-ray Newton’s rings (NRs) were found by reflective imaging at the early stages of the ablation dynamics. The soft X-ray NRs are caused by the interference between the bulk ablated surface and nanometer-scale thin spallation layer. The spallation layer was kept at the late timing of the ablation dynamics, and the height of that reached over 100 μm. The temporal evolution of the bulk ablated surface was observed in the ablation dynamics. From these results, we have succeeded in obtaining the temporal evolution of the ablation front exfoliated from the gold surface.

Generation of periodic arrangements of matter on materials irradiated by laser fields of uniform and isotropic energy distribution is a key issue in controlling laser structuring processes below the diffractive limit. Using three-dimensional finite-difference time-domain methods, we evaluate energy deposition patterns below a material's rough surface [1] and in bulk dielectric materials containing randomly distributed nano-inhomogeneities [2]. We show that both surface and volume patterns can be attributed to spatially ordered electromagnetic solutions of linear and nonlinear Maxwell equations. In particular, simulations revealed that anisotropic energy deposition results from the coherent superposition of the incident and the inhomogeneity-scattered light waves. Transient electronic response is also analyzed by kinetic equations of free electron excitation/relaxation processes for dielectrics and by ab initio calculations for metals. They show that for nonplasmonic metals, ultrafast carrier excitation can drastically affect electronic structures, driving a transient surface plasmonic state with high consequences for optical resonances generation [3]. Comparing condition formations of 2D laser-induced periodic surface structures (LIPSS) and 3D self-organized nanogratings, we will discuss the role of collective scattering of nanoroughness and the feedback-driven growth of the nanostructures.

[1] H. Zhang, J.P. Colombier, C. Li, N. Faure, G. Cheng, and R. Stoian, Physical Review B 92, 174109 (2015).

[2] A. Rudenko, J.P. Colombier, and T.E. Itina, Physical Review B 93 (7), 075427 (2016).

[3] E. Bévillon, J.P. Colombier, V. Recoules, H. Zhang, C. Li and R. Stoian, Physical Review B 93 (16), 165416 (2016).

Ultra-short pulsed lasers offer a great potential in precise and efficient material processing. Experimental and theoretical studies on efficiency of laser material processing from metals have demonstrated a high degree of dependency on the laser pulse duration. Within these studies, the investigation of the transient energy deposition in material takes a great significance for the thermal and mechanical material response after laser irradiation. The scope of this study was to investigate the ultra-fast energy deposition in a copper metal during the irradiation with a 680 fs ultra-short laser pulse at a 1056 nm and a 528 nm wavelength. For this purpose, a numerical analysis of the laser-matter interaction was performed by using the optical Drude critical point (DCP) model and thermal two temperature model fully coupled with thermoelasticity theory (2T-TE). The DCP model was incorporated into the 2T-TE to simulate the ultra-fast laser energy deposition and optical material response of copper. For comparison with experimental data a pump probe ellipsometry set-up was used. The pumpprobe ellipsometry set-up combines the high temporal resolution of pump-probe technique and ellipsometric measurements of optical indices. It was found numerically that a dynamic change on re ectivity and optical penetration depth at 1056 nm is mainly induced by a rapid temperature increase. In contrast at the irradiated wavelength of 528 nm the laser pulse absorption is mainly described by the interplay of the the interband excitation and intraband heating of conduction band electrons The time resolved simulation of optical indices (n, k) confirms the temporal experimental observation of refractive index and extinction coefficient within the first 10 ps from pump-probe ellipsometry set-up.

Previously the influence of picosecond laser spot size on ablation depth and threshold fluence on copper has been experimentally investigated. In order to have a comprehensive understanding of the corresponding mechanisms for high laser fluence cases, in which the laser fluence is several folds larger than the optimal ablation fluence, an axisymmetric 2D model, combining modified Two Temperature Model (TTM) and hydrodynamics, was developed. Since the dense vapor and plasma shielding effects have a significant impact on the absorbed energy of incident laser on the material surface, especially for the situation where the laser fluence is higher than vaporization threshold, several assumptions were made. It was roughly supposed that when the lattice temperature reaches 0.9T_c (T_c denotes the critical temperature of copper) dense vapor forms above the surface of the material due to the homogenous nucleation within the superheated melted layer, and once the surface temperature exceeds T_c stronger absorption of incident laser by plasma starts to play a crucial role. As the optical thickness of both dense vapor and plasma were supposed to be constants, correspondingly, the transmittance of both layers were approximately evaluated. Furthermore, as generally supposed in the literature, considerable energy loss caused by homogenous nucleation was also taken into account once the surface temperature of the lattice increased to 0.9T_c, and the melted material was treated as weakly compressible laminar flow with low Mach number (Ma<0.3). The numerical results indicate that the kinetic energy of the evaporated material increases when the laser spot size decreases, which could be a possible mechanism of the deeper ablation depth per pulse observed in the experiments with smaller laser spot sizes. Due to the occurrence of phase explosion, the surface temperature keeps constantly around 0.9T_c, and the intensive evaporation could remain the temperature at T_c until the establishment of equilibrium of both subsystems. Finally, the calculated evaporated mass has the same order of magnitude as the corresponding experimental data.

Superimposed multiple shots of low-fluence femtosecond (fs) laser pulses form a periodic nanostructure on solid surfaces through ablation. We have demonstrated that the self-organization process of nanostructuring can be regulated to fabricate a homogeneous nanograting on the target surface in air. A simple two-step ablation process and an ablation technique using interfering fs laser beams were developed to control plasmonic near-fields generated by fs laser pulses. The results have shown the nature of a single spatial standing wave mode of surface plasmon polaritons of which periodically enhanced near-fields ablate the target surface, to fabricate the nanograting on gallium nitride (GaN) and metals such as stainless steel (SUS) and titanium (Ti).

Direct writing using single or multiple energized beams (e.g. laser, ion or electron beams) provides high feature resolution (<1μm) compared with other solution-based printing methods (e.g. inkjet printing). There have been extensive researches on micro/nano additive manufacturing methods employing laser (or optical) and ion/electron beams. Many of these processes utilize specially designed photosensitive materials consisting of additives and effective components. Due to the presence of additive (such as polymer and binders), the effective components are relatively low resulting in high threshold for device operation. In order to direct print functional devices at low cost, there has been extensive research on laser processing of pre-synthesized nanomaterials for non-polymer functional device manufacturing. Pre-synthesized nanocrystals can have better control in the stoichiometry and crystallinity. In addition, pre-synthesis process enjoys the flexibility in material choice since a variety of materials can be synthesized. Femtosecond laser assembly and deposition of nanomaterials can be a feasible 3D micro/nano additive manufacturing approach, although mechanisms leading to assembly and deposition have not been fully understood. In this paper, we propose a mechanism for 2D and 3D deposition of nanocrystals by laser excitation with moderate peak intensities(10¹¹-10¹² W/cm²). It is postulated that laser induced charging is responsible for the deposition. The scheme paves the way for laser selective electrophoretic deposition as a micro/nanoscale additive manufacturing approach.

Ceramic materials are used extensively in the microelectronics, semiconductor, and LED lighting industries because of their electrically insulating and thermally conductive properties, as well as for their high-temperature-service capabilities. However, their brittleness presents significant challenges for conventional machining processes. In this paper we report on a series of experiments that demonstrate and characterize the efficacy of pulsed nanosecond UV and green lasers in machining ceramics commonly used in microelectronics manufacturing, such as aluminum oxide (alumina) and aluminum nitride. With a series of laser pocket milling experiments, fundamental volume ablation rate and ablation efficiency data were generated. In addition, techniques for various industrial machining processes, such as shallow scribing and deep scribing, were developed and demonstrated. We demonstrate that lasers with higher average powers offer higher processing rates with the one exception of deep scribes in aluminum nitride, where a lower average power but higher pulse energy source outperformed a higher average power laser.

Heat-sensitive materials, such as polymers, are used increasingly in various industrial sectors such as medical device manufacturing and organic electronics. Medical applications include implantable devices like stents, catheters and wires, which need to be structured and cut with minimum heat damage. Also the flat panel display market moves from LCD displays to organic LED (OLED) solutions, which utilize heat-sensitive polymer substrates. In both areas, the substrates often consist of multilayer stacks with different types of materials, such as metals, dielectric layers and polymers with different physical characteristic. The different thermal behavior and laser absorption properties of the materials used makes these stacks difficult to machine using conventional laser sources.

Femtosecond lasers are an enabling technology for micromachining of these materials since it is possible to machine ultrafine structures with minimum thermal impact and very precise control over material removed. An industrial femtosecond Spirit HE laser system from Spectra-Physics with pulse duration <400 fs, pulse energies of >120 μJ and average output powers of >16 W is an ideal tool for industrial micromachining of a wide range of materials with highest quality and efficiency. The laser offers process flexibility with programmable pulse energy, repetition rate, and pulse width. In this paper, we provide an overview of machining heat-sensitive materials using Spirit HE laser. In particular, we show how the laser parameters (e.g. laser wavelength, pulse duration, applied energy and repetition rate) and the processing strategy (gas assisted single pass cut vs. multi-scan process) influence the efficiency and quality of laser processing.

Thanks to the past years’ development efforts towards higher average power levels, higher repetition rates and, of course, improved robustness, ultra-short pulsed lasers have been able to enter more and more industrial 24/7-production areas. Despite some exceptions, where ultrashort-pulsed lasers with very high repetition rates are used to weld glass and other sensitive materials, the majority of industrial applications are related to material removal or the use of non-linear effects in transparent materials.

An interesting feature of ultra-short pulsed lasers in MOPA-configuration is the so-called “burst” mode. It provides pulse packages at nanosecond separation using programmable power slopes. Thus, the energy distribution of the pulses within a burst can be adjusted to the specific application task. Using burst pulses, laser-material-interaction is brought into a different regime, as subsequent pulses hit preconditioned material and plasma effects can be used effectively.

Burst pulses can help optimizing surface quality and ablation rates of engraved structures simultaneously. For laser filamentation of transparent and brittle materials, burst pulses provide filaments lengths of several millimeters.

In this paper, micro-processing of three kinds of super-hard materials of poly-crystal diamond (PCD)/tungsten-carbide (WC), CVD-diamond and cubic boron nitride (CNB) has been systematically studied using nanosecond laser (532nm and 355nm), and ultrafast laser (532nm and 515nm). Our purpose is to investigate a full laser micro-cutting solution to achieve a ready-to-use cutting tool insert (CTI). The results show a clean cut with little burns and recasting at edge. The cutting speed of ~2-10mm/min depending on thickness was obtained. The laser ablation process was also studied by varying laser parameters (wavelength, pulse width, pulse energy, repetition rate) and tool path to improve cutting speed. Also, studies on material removal efficiency (MRE) of PCD/WC with 355nm-ns and 515nm-fs laser as a function of laser fluence show that 355nm-ns laser is able to achieve higher MRE for PCD and WC. Thus, ultrafast laser is not necessarily used for superhard material cutting. Instead, post-polishing with ultrafast laser can be used to clean cutting surface and improve smoothness.

We developed a longitudinally excited CO₂ laser with a long external cavity and investigated the drilling characteristics of polycarbonate resin. The CO₂ laser was very simple and consisted of a 45-cm-long alumina ceramic pipe with an inner diameter of 13 mm, a pulse power supply, a step-up transformer, a storage capacitance, and a long external optical cavity with a cavity length of 175 cm and an aperture of 9 mm. The CO₂ laser produced a short pulse that had a spike pulse with the width of 282 ns and the energy of 0.45 mJ, a pulse tail with the length of 66.9 μs and the energy of 15.65 mJ, and a good circular beam. In a processing system, a ZnSe focusing lens with the focal length of 50 mm was used and the location of the focal plane was that of the sample surface. In the drilling of polycarbonate resin by the CO₂ laser, the drilling characteristics depended on the number of pulses and the fluence was investigated. Clear drilling without carbonization was produced by the irradiation of 50 pulses or less with the fluence of 19 J/cm² and the irradiation of 100 pulses or less with the fluence of 8 J/cm². The clear drilling with the deepest depth in this work was 403 μm at the 50 pulses irradiation with the fluence of 19 J/cm². The number of pulses and the fluence can control thermal influence in the CO₂ laser processing of polycarbonate resin.

The increasing demand for reliable, compact and low-cost optical components has been driving the development of very high precision glass shaping platforms. In the medical field for example, ball lenses are used for eye surgery or diffusors to destroy cancer cells in tumors, ball lenses are also used with catheters for the purposes of illumination during laparoscopic surgery. The fabrication of these all-fiber miniature components requires a high level of motion accuracy along with a well-controlled heating technology. Carbon dioxide (CO2) lasers are proven to be the most responsive heating source that offers the flexibility and resolution needed for the fabrication of these optical components. In this paper, we propose a novel glass temperature stabilization technique that improves the accuracy of heating with a CO2 lasers. This method is based on direct measurement and active stabilization of the glass temperature and can be used to enable the processing of specialty glasses, to increase the level of process control and improving manufacturing throughput yields.

Zinc oxide films are used as a photovoltaic transparent electrodes for current collection. They are a good substitute for expensive transparent electrodes on the basis of Indium tin oxide. The ZnO films fabricated with a certain morphology of the structure are able to act as a light diffuser. When passing through a layer of this material solar radiation quantum changes its trajectory, so dispersion of radiation occurs, which leads to an increase in the optical path of the particle in the photoactive structure.

We demonstrated beam shaping to top-flat and square by phase-only Spatial Light Modulator (SLM) and spatial frequency filtering. Spatial phase distribution of a femtosecond laser beam was modulated by a phase grating pattern reflecting a transfer function for beam shaping. By filtering the higher spatial frequency component at Fourier plane in 4f system, the spatial amplitude distribution of the zero-order beam was shaped to top-flat and square. This result enables us to fabricate large area and uniform devices by using multi-shot processing.

For higher cell-to-module efficiency in Cu(In,Ga)Se₂ (CIGS) thin-film solar cells, it is important to reduce the loss of active area due to integrated connection. The integrated connection contains three scribing processes: P1 (back contact insulation), P2 (electrical connection) and P3 (transparent conductive oxide, shortly TCO front contact insulation). In this work, we focused on ultrashort-pulse laser scribing (λ=1034 nm, Δτ=300 fs) of TCO via lift-off process as damage-less P3 scribing of CIGS thin-film solar cells. The lift-off of TCO was caused by laser ablation of only an upper part of CIGS light-absorbing layer. The dependence of lift-off behavior on the laser pulse energy and TCO film thickness has been investigated. It was observed that the lift-off of TCO formed a heat-affected zone (HAZ) with a thickness up to 250 nm beneath the trench bottom, where the CIGS experienced to melt. Further, thinner TCO film required lower laser energy threshold for the TCO lift-off, which is favorable to higher solar cell efficiency due to smaller HAZ. Using the TCO liftoff as P3, a submodule with an active area of approximately 3.5 cm² made by all laser scribing exhibited the conversion efficiency of 11.6 %. After post-annealing at 85 °C for 15 h in vacuum for recovering laser-induced damages, the efficiency was successfully improved to 15.0 %, which is comparable to mechanically-scribed one.