This PDF file contains the front matter associated with SPIE Proceedings Volume 10906, including the Title Page, Copyright information, Table of Contents, and Conference Committee listing.

Laser processing using femtosecond laser pulses has been emerging as a powerful tool for micromachining and surface functionalization owing to its precise processing capability, and the understanding of light-matter interactions is of great importance for the optimization. One big challenge in understanding laser ablation processes during microprocessing is to understand influences of surface morphology, which can substantially change the light-matter interaction. Pulses after the first shot experience changes in the surface morphology that are induced by the prior pulses during multi-shot irradiation. To investigate the relation between the surface morphology and the laser ablation processes during multi-shot irradiation, we developed an in-situ three-dimensional depth profile measurement system with nanometer precision. Our system enabled pulse-by-pulse monitoring of the surface morphology changes so that we can investigate the changes in depth profile induced by laser ablation during multi-shot irradiation. The experimental system consisted of a 1-kHz femtosecond laser, and a white-light interferometry microscope, which was synchronized with the regenerative amplifier. Notably, the changes in the depth profile less than a few tens of nanometers were precisely measured, and the changes strongly depended on the original surface morphology and the laser fluence. We performed systematic measurements on the changes in depth profile as a function of laser fluence and the number of irradiated pulses with various material, and conclude that laser-induced embrittlement of a target material plays a decisive role to determine the ablation rate during multiple-pulse irradiation.

During the 1980s, the medical community embraced titanium as the material of choice for implantable devices destined to be attached to bone. Numerous studies presented titanium’s osseointegration characteristics and further research documented the positive impact of textured, functional surfaces on osseointegration. Compared to smooth “as-machined” surfaces, texturing not only improves bone integration and thus implant stability; it also allows for the growth of supportive tissue and may even provide antibacterial advantages. Today, the gold standard for titanium implants features a textured surface on all areas where integration with bone needs to take place. These functional textured surfaces are found on diverse devices such as bone plates, hip joints, and cervical and dental implants.

The challenge to create corrosion resistant marks and labeling has spanned across many industries that require robust traceability methods including medical devices and instruments. The unique properties of ultrashort laser pulses enable precise surface structuring to withstand the required manufacturing post-processes of passivation and autoclaving. The benefits of ultrashort laser marking are demonstrated with the results in a comparison to traditional nanosecond laser marking systems through observation of pulse energy and pulse duration effects, corrosion resistance and long term durability under clinical conditions on medical grade alloys. Moreover, an analysis of microstructure by use of EDX and XRD exhibits a visual advantage of formed laser induced periodic surface structures (LIPSS) evident only to ultrashort pulse marking techniques. Under this new approach the allowable process parameter window flexibility for varied material types specific to medical applications was noted with respect to pico- and femtosecond pulse techniques. Traceability through unique device identification (UDI) is realized by combining complimentary technologies to format compliant sequenced data. Such data has been demonstrated as verifiable and rated with a customized grade to ensure quality of the marked code. The read-out data as well as the quality grading of marking result can be further processed in the production environment for documentation reasons. Thereby, the obstacle of UDI and corrosion resistant marking for medical devices and instruments can be met with such an industrial solution.

Bessel beams are invariant solutions to the Helmoltz equation that can also propagate, with finite pulse energy at high intensity, in a quasi-invariant regime in transparent dielectrics. Homogeneous energy is deposited along a line focus by infrared ultrashort pulses. If the cone angle is sufficiently high, the laser-deposited energy density is enough to open nanochannels in glasses or sapphire with a single laser pulse. This has found applications in the field of glass cutting via the technique of "stealth dicing". Here we address two important challenges in this field. First, high quality Bessel beams are essential for controlled energy deposition. Second, the maximal angle used up to here for channel drilling was 26° for 800 nm laser central wavelength. This enabled the formation of channels with diameters down to typically 300 nm in glass and sapphire. It is questionable if higher cone angles could also produce channels with potentially smaller diameters. Here, we generate high quality Bessel-Gauss beams with a setup based on reflective, off-axis axicons. The Bessel zone exceeds 100 µm for cone angles up to 35 degrees. This corresponds to central spot diameter down to 0.5 µm FWHM. We qualified these beams with a 100 fs laser source centered at 800 nm wavelength. We report nanochannel drilling down to typically 100 nm over at least 30 µm length in glass. Our approach opens novel perspectives for high quality Bessel beam generation but also for the highly confined laser-matter interaction for high precision processing of transparent dielectrics.

Polycrystalline diamond cutting tools are widely used for drilling and turning applications due to their high wear resistance and long durability, however the issue of adhesion of workpiece to the cutting tool significantly affects the cutting tool lifetime. Using a nanosecond fibre laser surface texturing of polycrystalline diamond single point cutting tools is proposed to improve diamond wear and anti-adhesion properties in machining aluminium alloys. The textures, with topographical features’ depths and pitch ranging from tens of nanometers to tens of micrometers, were first milled using a fibre laser (1064-nm wavelength) at different fluences, feed speeds and pulse durations, and finally characterised using a combination of Scanning Electron Microscopy, White Light Interferometry and Energy Dispersive X-Ray (EDX). The effect of different textures on the wear properties was investigated in turning tests under dry conditions. The tests were stopped every 20 passes and the wear analysed through an Alicona optical 3D measurements. The online monitoring and post-processing of the cutting forces and the microscopical characterisation of the tested cutting tools allowed the evaluation of the effects of texture design and adhesive properties. For textures depths in the order of 260nm and post process roughness in the order of tens of nanometers, a reduction of cutting force and an improvement of antiadhesive effect were achieved in dry turning.

Ultrafast laser processing has diverse scientific, industrial and medical applications. Until recently, this process has been idealized as a one-way interaction — the laser beam modifies the material, which would be the end of the story. The idea of the material modifying the laser beam, in return, and that this could open new doors appears to have been overlooked. In many cases, such two-way interactions either did not occur, or were unnoticed, if present, and actively prevented, if noticed. Our approach is to explicitly design for and exploit such interactions, and this approach has already led to several striking advances. Here, we invoke nonlinearities in the form of positive feedback between laser beam-induced changes in the material and material change-induced effects back on the laser beam. We first showed that we could create laser-induced spatial nanostructures on various material surfaces with unprecedented uniformity (Ilday et al., Nature Photon., 2013), which we later extended to creation of self-organized 3D structures inside silicon (Ilday et al., Nature Photon., 2017). This perspective also led to the extremely efficient regime of ablation-cooled laser-material ablation (Ilday et al., Nature, 2016), self-assembly of colloidal nanoparticles (Ilday et al., Nature Commun., 2017), and intracavity optical trapping, where the trap is placed inside the cavity of a laser, giving rise to nonlinear feedback forces (arXiv:1808.07831).These demonstrations will be discussed, compared and contrasted.

The material processing by DUV laser region has been required for wide band gap material and precise hole and groove in DUV region. It is still very hard to get high power solid-state lasers in this spectral region especially below 300 nm. The rare-gas halide excimer lasers are only the solution, and now the time has come to examine the new applications of material processing with DUV excimer lasers. 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. In this method, it is possible to process fine patterns and various patterns. We processed using Ajinomoto build-up films (ABF) as organic material. The types of ABF were GX92, GX-T31 and GY50, and their thickness was 10 μm. We confirmed that it is possible to process via of 5 μm or less in build-up film. Furthermore, it was confirmed that the L/S pattern can be processed. We will report the result of processing organic materials with 248 nm excimer laser.

Glass light pipes are fabricated using femtosecond laser irradiation followed by etching and thermal processing for minimizing sidewall scattering loss due to surface roughness. Turning mirrors and combiners, or splitters, are demonstrated. A critical step is assembly of the light pipe for coupling to a source or detector, which requires alignment and attachment, typically to a substrate. A combination of such structures has been realized to aid in assembly and optical transmission efficiency. Coupling from a distributed source through a lens array and into a light pipe array has been pursued for a waveguiding solar concentrators. The opposite propagation direction enables LED coupling and light distribution. Light pipes are fabricated with large cross-sectional areas, up to several square millimeters, compared to optical fibers. For glass-to-air cladding, the numerical aperture is substantially larger than for most optical fibers, thus enabling low loss transmission for high etendue sources. Instead of coating with a lower index material, as with optical fibers, a holding structure is desired to maximize the angular range for total internal reflection. We discuss the issues related to surface scattering and losses due to the cladding and light pipe mechanical support for LED lighting and solar applications.

Ultrashort laser irradiation of metal targets results in a variety of coupled processes, such as energy deposition on surface, electron-ion heating and diffusion, as well as thermal ablation and plasma expansion, mechanical rupture below the surface, and melt flow, modifying the initial surface morphology on micro/nanometric scales. Multidimensional simulations capable to predict the consequences of inhomogeneous absorption on hydrodynamic processes are performed in order to elucidate the mechanisms of surface micro/nanostructure formation and material removal during multipulse laser ablation in regimes below, near and above laser ablation threshold. On one hand, the numerical results suggest new ways of control over the properties of periodic and aperiodic surface structures. On the other hand, the strategies to reduce the surface roughness and to improve the quality and the effciency of ultrashort laser ablation are discussed.

In this study, a surface pre-treatment method for applying a metallic coating on a fiber reinforced plastic substrate is presented. Laser structuring with a pulsed laser source is used to create structures on carbon fiber reinforced epoxy. A nickel-chromium coating is applied by atmospheric plasma spraying. A combination of matrix removal and trench structure exceeds industrial requirements. Using pull-off tests, an average adhesive strength of at least 20.3±2.7 MPa was achieved between the coating and the substrate before composite fracture was observed.

Inertial microfluidic particles sorting represents a critical task in many areas of biology, biotechnology, and medicine, including the isolation from blood of rare target cell populations, like e.g. circulating tumor cells (CTCs) and circulating fetal cells (CFCs). Usually, cell sorter microfluidic devices are fabricated by PDMS soft lithography, which is the most widespread micromanufacturing platform enabling to cost-effectively produce Lab-on-a-Chip with resolution in the nanometer scale. However, this technology presents some drawbacks: (i) due to PDMS softness, especially for high-pressure flows, the microfluidic behavior may change along the devices, leading to ambiguous results; (ii) soft-lithography allows to pattern structures on just one side of the chip thus limiting the affordable geometries to enhance the throughput of target particles. In this work, we develop a PMMA continuous size-based inertial microfluidic sorter by femtosecond laser microfabrication (FLM). The device design includes contracting and expanding channels (microchambers) provided with siphoning outlets on the backside of the chip. Since FLM technology is in principle applicable to any type of polymer, we chose PMMA, which is a biocompatible and transparent thermoplastic polymer much stiffer than PDMS. FLM allows machining the microfluidic network on both sides of the chip, making it possible the parallelization of the sorting process. In addition, thanks to the FLM flexibility, we easily varied the chambers number and the collecting strategy (at different flow rates) in order to define a device layout maximizing the trapping efficiency and throughput.

The hermeticity of microfluidic chips is a critical issue to ensure the functionality of the device. In this paper, we report methodology and results of transparent substrates micro-joining by ultra-short pulsed laser. The study has been focused on two materials usually used in microfluidic chips: cyclic olefin polymer (COP) and glass (borofloat). For both joining, the laser-matter interaction at the interface of the substrates was investigated. Pressure and leakage tests have also been performed to validate the microchips functionality. Furthermore, for the polymer-polymer joining, a new methodology for putting in contact the substrates has been developed. Based on electrostatic forces, this tool allows to uniformize the pressure needed to weld two substrates together. This is also a non-contact system which is less dependent on the flatness of the substrates. This paper presents the first results obtained with this technology. Finally, the research has been oriented in an industrial way i.e., same laser sources for both substrates, same optical system and optical elements allowing to process microfluidics chips on conventional substrates in a more flexible way.

The surface treatment of micro- and nanolayers by means of linear scanning with a line-shaped laser beam gains more and more importance for advanced products. Laser annealing of functional layers to enhance material properties is already an established process, e.g. for coatings on architectural glass or in advanced electronic components, such as flat panel displays. Due to their flexibility, anamorphic beam shaping and homogenization of high-power laser beams constantly find further applications in the selective heating of thin layers. One of these applications is debonding of flexible OLED displays, so called laser lift-off, which was introduced just in recent years. The performance of a laser lift-off system highly depends on the optical properties of the line beam. Good homogeneity in long axis direction, high energy density and sufficient depth of focus are crucial for reliable processing results. However, future system concepts will have to consider additional requirements of an industrial manufacturing environment as the application is maturing. We present a system for laser lift-off of flexible OLED displays, which focuses on a compact and rugged design. Starting from an existing system concept of a line focus system in the infra-red regime we define the requirements for a transition to the ultra-violet spectral range and discuss both, optical and mechanical layout. The optical key parameters are presented and validated by simulation and experiment. We demonstrate the implementation of a functional model.

In this work we present femtosecond laser lift off (LLO) technique for GaN coating separation from sapphire substrates. We demonstrate that using rapid raster scanning technique it is possible to achieve successful delamination of GaN coatings with low surface roughness without any stitching artifacts and at industrial processing rate. Several delamination regimes can be identified in femtosecond LLO: thermal decomposition, stress induced peeling. These results show that femtosecond laser LLO could surpass nanosecond LLO by the achieved quality and overall control of delamination processes.

The electrical properties of poly-Si thin films doped using KrF excimer laser irradiation with a phosphoric-acid coating were investigated. After laser doping, the mobility, carrier concentration, activation ratio, and contact resistivity of the poly-Si were found to be 61 cm² /Vs, 1.5×10¹⁸ cm^-3 , 18.1 %, and 8.5 × 10⁻⁵ Ω⋅cm² , respectively. Additionally, the operation of a bottom gate transistor fabricated using laser doping was realized and is described herein.

We demonstrate the use of femtosecond laser micromachining for ablating macro-sized cavities in crystalline silicon. The method employed is laser milling in which the focused laser beam is raster scanned over the area to be removed. We report the achievement of very high volume ablation rates for the cavity of up to 8.48x10⁶ μm³ s^-1. To achieve such high rates, we make use of a high average power fiber laser source of 1030 nm wavelength and variable per pulse energy of up to 100 μJ. By carefully controlling the process variables such as pulse energy, repetition rate and scanner speed, the tradeoffs between micromachining quality and ablation rate are quantified. The developed process is applied on Siliconon-Insulator (SOI) wafers for improving performance of RF devices. By making use of laser removal and an additional step of selective silicon etch using XeF₂, handler silicon is removed completely under RF circuits such as SP9T switch. The local removal of silicon under such circuits completely eliminates the losses and non-linearities caused by the coupling of RF signals to the semi-conducting substrate. Small-signal and large-signal RF measurements are performed before and after substrate removal to quantify the performance gain. The obtained performance after substrate removal is better than specialized RF-SOI substrates such as trap-rich SOI. This is of practical significance for next generation wireless technologies like 5G which operate at higher frequencies with stringent specifications. The proposed method is also potentially useful for fabricating membrane based devices in SOI technology such as pressure sensors.

The welding of glass using ultrashort laser pulse has attracted much attention due to its potential applications in many fields such as solar cells, implanted microelectronics, OLED, MEMS, micro sensors and so on. However the optical contact which requires a distance between two glasses less than 100 nm is a very harsh requirements in practical engineering applications. A welding method of glass, which adopts bursts sequences of ultrashort laser pulses oscillated in a small region to react more glass material and release heat stress gently, is presented in this paper. In this way, a stable and mild liquid pool with more melt glass can be achieved to weld glasses with large gap. The maximum gap distance between two glasses is almost 40 μm which is an order of magnitude higher than other methods, and the joint strength of the glass weld with the natural contact gap of 10 μm is up to 64 MPa. At last, the encapsulation experiment of the welding glass with a closed area was carried out to prove that the sample can guarantee good sealing in 100 hours.

Ultrashort lasers have gained widespread use for both scientific and industrial applications due to their highly efficient and precise material ablation properties. In order to optimise the interaction between the ultrafast laser source and the target an in-depth understanding of the optical and ablation dynamics is required. Here we present a study of the complete ablation dynamics ablation properties of the three most relevant metals (Copper, Aluminium and Stainless Steel) after ultrashort laser pulses for the first time. This is achieved through a temporal analysis of the change in the optical properties after laser irradiation using pump-probe ellipsometry and pump-probe microscopy. The complex refractive index change in the first 50 ps after laser irradiation is analysed with a 1 ps resolution using pump-probe ellipsometry. The results show a large decrease in the extinction coefficient k for all the analysed metals in the first few ps after the pulse impact. This indicates an early stage decrease in the material density due to unloading of the pressure buildup generated by the stress confinement state in the metal skin depth. This pressure buildup and density decrease results in phase change and material motion at time scales from 100 ps to 1 ns, which can be visualised with pump-probe microscopy. Depending on the metal, ablation mechanisms such as spallation and phase explosion can be visualised and followed into the equilibrium state at about 10 µs. The effects of the early stage dynamics can be used to describe ablation efficiency trends observed for double and pulse bursts of various inter-pulse delay times.

Femtosecond laser surface processing (FLSP) is a unique material processing technique that can produce self-organized micro/nanostructures on most materials including metals, semiconductors, and dielectrics. These structures have demonstrated the enhancement of surface properties such as heat transfer and broadband light absorption. The chemical composition and morphology of FLSP structures is highly dependent on processing parameters including background gas composition, pressure, laser fluence, and number of laser pulses. When the laser processing is carried out in open atmosphere, a thick oxide layer forms on the FLSP surface structures due to the high reactivity of the surface with the environmental constituents immediately after laser processing. In this work, N₂ and forming gas are used during laser processing in an effort to form a metal nitride on the surface of aluminum. Aluminum nitride is a promising material for enhancing the heat transfer performance of surfaces because of its thermal conductivity, which can be as high as 285 W/m-K, whereas aluminum oxide has a low thermal conductivity (30 W/m-K). Aluminum nitride incorporation into FLSP surfaces has the potential to act as a passivation layer to decrease the oxygen content and increase the thermal conductivity of the surface. Nitrogen incorporation is studied by applying FLSP in air, N₂, and a 95% N₂/5% H₂ mixture. The chemical composition of the FLSP surfaces is determined by X-ray photoelectron spectroscopy (XPS) and energy-dispersive X-ray spectroscopy (EDS). Cross-sectional analysis of the FLSP microstructures is performed using ion beam milling.

In this work, we report on the fabrication of laser induced periodic surface structures (LIPSS) on stainless steel, using bursts of 200 fs sub-pulses at a wavelength of 1030 nm. A cascade of birefringent crystals was used to generate the bursts with tunable number of sub-pulses and intra-burst delays varying between 1.5 ps and 24 ps. Being such a delay shorter than the typical electron-lattice relaxation time in metals, the sub-pulses impinge on the sample surface when the material is still in a transient state after excitation from the first sub-pulse, thus allowing peculiar structures to be generated depending on the burst features. We obtained 1-D and 2-D periodic surface structures and investigated the influence of number of sub-pulses and polarization on their morphology. In particular, when bursts composed by all-aligned linearly polarized sub-pulses were used, 1-D LIPSS were obtained with different periodicity and depths depending on the number of sub-pulses. Bursts with crossed linear polarization or circular polarization sub-pulses produced 2-D LIPSS with morphology varying from triangular structures arranged in hexagonal lattice to pillar-like ordered or disordered structures depending on the bursts features. In most cases these structures exhibit a superhydrophobic behavior, as assessed by static contact angle measurements, which is achieved after a time of exposition to laboratory air. By XPS analysis we investigated the chemical variations occurring on the surfaces over this time.

The advantages of the femtosecond laser for micromachining of materials have been widely demonstrated allowing the laser micromachining to reach a level of accuracy in the micrometer range level. However, most of the current femtosecond laser micromachining applications are for flat surfaces, 2D or 2.5D, requiring different kinds of machining: drilling, cutting, and texturing, for more and more exotic materials. Biomedical implants are a part of those new objects requiring very high level of accuracy and surface finish, and for complex geometries: cylindrical or hemispherical shapes. LASEA has developed a system combining femtosecond laser with 7 simultaneously moving axes: 5 mechanical axes and 2 galvanometric axes. This combines the 3D micromachining offered by the 5 axes with the fast scanning. The laser parameters and strategies are controlled owing to laser specific developed functionalities. Another challenge to overcome is the research of laser parameters which is time and material consuming. In order to make this research more efficient, LASEA has developed a tool named LS-Plume which simulates the profiles for different sets of parameters. In this work, we focus mainly onto biomedical implants, such as stent cutting and hip implants texturing. The characterisation of the stents was carried out based on computed X-ray tomography, after processing and balloon inflation. Fast texturing of 3D part is also demonstrated and evaluated. Different biocompatible materials have been characterised and used by the tool LS-Plume. Showing a good match between a simulated and measured profiles.

The use of self-organized micro/nanostructured surfaces formed using femtosecond laser surface processing (FLSP) techniques has become a promising area of research for enhancing surface properties of metals, with many applications including enhancing heat transfer. In this work, we demonstrate advantages of the use of dual-pulse versus single-pulse FLSP techniques to produce self-organized micro/nanostructures on copper. With the dual-pulse technique, the femtosecond pulses out of the laser (spaced 1 ms apart) are split into pulse pairs spaced < 1 ns apart and are focused collinear on the sample surface. Single-pulse FLSP techniques have been widely used to produce self-organized “mound-like” structures on a wide range of metals including a number of stainless steel alloys, aluminum, nickel, titanium, and recently on copper. Due to its high thermal conductivity, copper is used in many critical heat transfer applications and micro/nanostructured copper surfaces are desired to further improve heat transfer characteristics. Using single-pulse (pulses spaced 1 ms apart) FLSP techniques, self-organized microstructure formation on copper requires much higher pulse fluence than is commonly used for producing microstructures on other metals, which results in instabilities during laser processing (non-uniform surfaces), low processing efficiency, and limitations on the control of the types of structures produced. In this paper, we report results that demonstrate that the dual-pulse FLSP technique can be used to produce microstructures on copper more efficiently than using single-pulse FLSP, with better control of the surface structures produced. Cross-sectional subsurface microstructure analysis is also presented for single-pulse versus dual-pulse FLSP functionalized copper surfaces.

Surfaces with well-defined features (e.g. periodic structures) have shown to exhibit outstanding properties. The design of these textured surfaces often follows a biomimetic approach motivated by living organisms which developed over time through natural selection and evolution. The efficient production of these versatile patterns still represents one of the greatest technical challenges today in the development of new customized surface functionalities. Direct Laser Interference Patterning (DLIP) has been identified as an outstanding technology for the efficient fabrication of tailored surface structures. This method can show impressive processing speeds (up to 1 m²/min) as well as a superior flexibility in producing extremely versatile surface structures. This work gives an overview about recent developments of the DLIP technology by focusing on the topics: structure flexibility, process productivity, technical implementations and recent examples of achieved surface functionalities.

The sub-µm- and nanostructured thin metal layers and dielectric surfaces exhibit manifold applications. However, the fast, easy and cost-effective fabrication is still a challenge. A possible technological solution is laser-induced self-organized processes like IPSM-LIFE (laser-induced front side etching using in-situ pre-structured metal layer). At IPSM-LIFE, a metal covered dielectric is irradiated where self-organized molten metal layer deformation process assists the structuring. A chromium-fused silica system was irradiated by a KrF excimer laser (λ = 248 nm, Δt_p = 25 ns, f = 100 Hz). The IPSM-LIFE can be divided into two steps: STEP 1 and STEP 2. At IPSM – LIFE - STEP 1: The laser irradiation of thin metal layers on dielectric surfaces results in a melting and consequently in a nanostructuring process of the metal layer. The laser treatment induced a large-area modification of the sample surface. These modifications allow a macroscopic adjustment of the optical properties as well as of the water contact angle. The transmission can be variated from ~3 % to ~ 74 % for visible light and the water contact angle from < 5° to ~ 97°. The localized modification of the optical properties allows the fabrication of high-resolution greyscale images. Furthermore, the pre-structured metal layer can be used as a mask for a reactive ion beam etching (RIBE) of the SiO₂. The RIBE process allows the fabrication of sub-µm glass structures with a diameter down to 30 nm and a high aspect ratio (>10) at the same time. At IPSM-LIFE - STEP 2: A subsequent high laser fluence treatment of the pre-structured metal layer results in a structuring of the underlying dielectric surface. The RIBE and IPSM-LIFE structured fused silica surface exhibits water contact angle up to 105°. The resultant surface topography was analyzed by optical (OM), atomic force (AFM) and scanning electron microscopy (SEM).

Low spatial frequency Laser-induced Periodic Surface Structures (LSFL) have been created on single crystal silicon with picosecond laser pulses with a wavelength of λ =1030nm with varying laser spot diameters obtained by a defocused laser beam. The laser processing parameters have been adjusted theoretically and experimentally to obtain similar LSFL for all studied laser spot diameters. The periodicity and amplitude of the LSFL were measured by SEM and AFM analysis. It has been found that the periodicities of the LSFL do not change when LSFL were created with larger laser spot diameters. The amplitudes of the LSFL decrease with increasing laser spot diameters, although this correlation is not strong.

Surface structuring has attracted great attention due to the rising need of the industrial sector to improve their products through surface functionalization. A very promising technology for this purpose is Direct Laser Interference Patterning, which implements interference of multiple beams to directly form periodical patterns with a single laser pulse. This provides the ability to utilize the whole laser power for high speed structuring of large surface areas. However, in some cases even higher speeds are required. Therefore, alternative technologies like roll-to-roll hot embossing must be utilized. By the synergy of the DLIP technology, which is used for structuring the sleeves (embossing tool) and the roll-to-roll hot-embossing method, the throughput for the fabrication of micro/nano structured polymer foils can be increased at least one order of magnitude. Furthermore, since the sleeves are processed directly, without the need of lithographic methods, the fabrication cost of the textured sleeves can be significantly reduced (up to ~ 90%). In this study, a unique DLIP-workstation is introduced, consisting of a ps-laser, several DLIP optics and a special positioning system for cylindrical parts. The system allows the patterning of cylindrical parts up to 600 mm in length and 300 mm in diameter. The structures, consisting of line-like or dot-like patterns with periods ranging from 5.5 µm down to 1.0 µm, can be produced with record processing speeds up to 5700 mm²/min. Finally, the implementation of these structured sleeves in a roll-to-roll system is demonstrated for imprinting polymer foils at an impressive surface throughputs of 12.5 m²/min, corresponding to web-speeds of 50 m/min. Additionally, some examples of the decorative elements processed by these technique are presented.

This study reports on the application of the Direct Laser Interference Patterning method for the fabrication of holographic motives. The advantages of this method over conventional laser processing methods in terms of resolution, flexibility and throughput are analyzed. It is showed that interference approach for formation of diffraction gratings provides faster fabrication speed together with enhanced visual effect of the structural colors. The control of the period of the formed patterns provided the ability to form exact structural colors, which preserved the visibility of the motives across the whole structured area at certain observation conditions. The capability to improve further the fabrication speed, required for several industrial applications, is demonstrated using a Roll-to-Roll hot embossing system, permitting to replicate holographic motives formed by DLIP on PET foils. Finally, the first tests of inline monitoring method are presented, which is proposed for controlling the quality of the imprinted structures.

The ability to employ spatially-selective control of refractive index and dispersion variation with a high magnitude of change is essential for the realization of functional infrared graded-index (GRIN) components. Thin films fabricated from multi-component GAP-Se glass-ceramic materials were processed using nanosecond laser radiation at the wavelength λ = 2 μm. Various irradiation and post-processing protocols were implemented to maximize the magnitude of the local refractive index change, and to quantify the evolution of the glass to glass ceramic ‘conversion’ on optical material physical properties. Irradiation of films possessing various thicknesses from 1 to 25 μm was performed using area-scan patterns, while the average laser power and the number of scans were varied. Irradiated materials were subsequently heat-treated, and the local refractive index was determined for different durations of the heat treatment. Depth-dependent composition and film morphology characterization of as-deposited films was evaluated, and surface morphology of the post laserprocessed and heat-treated areas was studied to evaluate effects on the photo-thermal refractive index change associated with nanocrystal formation. Initial studies demonstrated a maximum positive refractive index change of ▵n ≈ 0.07 in a broad spectral range in the infrared which scales with film thickness and exposure dose while maintaining required optical quality.

Materials processing using femtosecond laser pulses offers the potential for high-precision manufacturing. However, due to the associated nonlinear processes, even small levels of experimental noise (e.g. instability in laser power, or unexpected debris) can result in substantial deviations from the desired machined structures. There is therefore much interest in the development of closed-loop feedback processes. Recent advances in the algorithms behind neural networks, and in particular convolutional neural networks (CNNs) have led to rapid advancements in the field. Here, we will present the first demonstration of the application of a CNN for observing and identifying the experimental parameters exclusively from a camera that observes the sample during laser machining. We will show that the CNN was able to accurately determine the laser fluence, number of pulses and the material used. Although there are many other computational approaches for image-based feedback, this CNN approach has the significant advantage that it works purely as a pattern recognition device, and hence requires minimal human input with regards to the physical processes that underlie the laser machining process. Therefore, this avoids the need for a comprehensive programmatical description of the nonlinear interaction of laser light and material. Training time was one hour, and the time to process and identify the experimental parameters from a single image was approximately 30 milliseconds, hence showing the potential for a CNN to act as the central component of a real-time feedback system for laser machining, and enabling undesired or incorrect machining to be immediately compensated.

In the last years LIPSS based processes leap from the research laboratories to industrial applications, in particular for tribology, polymer mold texturing, colorizing and enhanced biocompatibility. Despite of these applications not all the phenomena underlying LIPSS generation were understood and a comprehensive model to explain all the cases is generally accepted. In this work a phenomenological explanation of the level of regularity achievable when patterning different materials is proposed and discussed. In particular the regularity is correlated to the ratio between the laser wavelength and the decay length of the surface electromagnetic waves induced on the metallic surfaces. Regularity is measured by means of an original parameter, the Dispersion of the LIPSS Orientation Angle (DLOA). DLOA is calculated for different materials and parameters obtained both from original experiments and from literature and the results are the basis of the phenomenological model presented in the work. In the model the effects of the material dielectric permittivity and its dependency by time immediately after the irradiation are simulated and the effects of spot size is critically discussed.

Electrospun polylactide (PLA) nanofiber nonwovens are promising candidates for applications in tissue engineering. They may combine the advantageous chemical properties of PLA with a highly porous three-dimensional structure, which promotes the transportation of nutrients and the cell proliferation into the scaffolds. In this work, we tested different laser micro material processing strategies to optimize the surface topography of PLA nanofiber nonwovens for cell attachment. It was found, that the wetting behavior of the nonwoven samples could be switched between a hydrophobic and a hydrophilic behavior by balancing laser induced thermal processes and gentle laser ablation.

Laser reduced graphene oxide-based interdigitated microelectrodes were functionalized with TiO₂ nanoparticles towards sensor applications. Two kinds of interdigitated microelectrodes were prepared by laser direct writing using graphene oxide (GO) and TiO₂ nanoparticles. One is a TiO₂ nanoparticle-deposited interdigitated microelectrode consisting of GO and laser-induced reduced graphene oxide (rGO), where the rGO/GO/rGO structure was prepared by laser direct writing on a GO-coated PET film and then a TiO₂ sol solution was drop-casted on the electrode. Another is a TiO₂/rGO hybrid interdigitated microelectrode prepared by laser direct writing on a TiO₂ nanoparticle-GO hybrid film. The UV light sensitivity of the TiO₂ nanoparticle-deposited rGO/GO/rGO interdigitated microelectrode and the oxygen quenching behavior were applied to oxygen sensing. The output voltage from the TiO₂ nanoparticle-deposited rGO/GO/rGO structure in the AC detection mode under 369 nm LED irradiation showed clear relationship with the degree of vacuum. The sensing behavior was based on the photo-generated carrier quenching by oxygen. The irradiation of a 405 nm blue violet laser to a TiO₂ nanoparticle-GO hybrid film caused the crystal phase transition from anatase to rutile TiO₂ accompanying the melting of anatase nanoparticles. The TiO₂/rGO hybrid interdigitated microelectrode consisting of anatase TiO₂, rutile TiO₂, and rGO was prepared by laser direct writing. The TiO₂/rGO hybrid interdigitated microelectrode showed the response to visible light irradiation.

The realization of micro-disk resonators (MDRs) of high quality (Q) factors using lithium niobate on insulator (LNOI) as the substrate has spurred great interest in developing on-chip nanophotonic structures which hold the promise for efficient nonlinear wavelength conversion, fast electrooptic light modulation, and high density photonic integration. Here, we report on fabrication of crystalline lithium niobate microresonators with quality factors above 10^7 as measured around 770 nm wavelength, which is almost one order of magnitude higher than the state-of-the-art Q factors around the visible and near-infrared wavelengths reported so far. Our fabrication process includes four steps. First, a thin layer of chromium (Cr) was deposited on the surface of the LNOI by thermal evaporation coating. Subsequently, the Cr film on the LNOI sample was patterned into a circular disk using space-selective femtosecond laser direct writing. Next, the chemo-mechanical (CM) polishing process was performed to fabricate LN MDRs by a wafer polishing machine, the surface smoothness is greatly improved by the CM polishing process, leading to a significant increase of the Q factor. Finally, the fabricated structure was first immersed in Cr etching solution, and then underwent a chemical wet etching in a buffered hydrofluoric acid (HF) solution to partially remove the SiO_2 layer beneath the LN microdisk to produce the freestanding LN MDRs. We have also demonstrated nonlinear processes including second harmonic generation and Raman scattering in our LN MDRs.

Gaussian intensity profiles are widely used in the field of laser material processing. Nevertheless, there are applications, where the inhomogeneous beam profile is not acceptable. We show that refractive beam shaping systems provide very good results for generating tailored focal intensity distributions, e.g. top-hat or doughnut shaped profiles. Even though using just one beam shaping system the width of the profiles is scalable. The device is suitable for working with a scanner and F-Theta lens as commonly used for material processing. Results of material processing of steel are compared for different focal intensity distributions.

In this study, an optical setup based on two phase-only spatial light modulators is presented, capable to shape two parallel laser beams. Each of the light modulators creates different and complementary Gaussian multi-spot distributions in the focal plane. By the polarization based combination of two differently shaped beams, a multi-spot beam profile with higher multi-spot density than for a single spatial light modulator setup can be obtained without speckles to appear. Beam shaping results are characterized by means of a beam profile camera and compared to a single spatial light modulator setup. Beam shapes generated by the presented setup are applied to ultrashort pulse laser ablation of metals. The potential of the presented optics is discussed regarding ground roughness and waviness of the ablated structure.

The high peak power of ultrashort laser pulses enables the processing of transparent materials by inducing absorption nonlinearly. There are already a variety of applications in the field based on volume or surface absorption. Spatial beam shaping offers high potential, for example by applying Bessel-like beams for single pulse full thickness modification in cutting applications. Temporal shaping the pulse or applying bursts of pulses adapted in amplitude and interval is a further option to localize and dose the energy deposition. An alternative option for scaling is processing at elevated repetition rates. This typically results in accumulation effects, often not desired, sometimes useful or even necessary for several applications. Learning about the complex interplay of the effects relevant for ultrashort pulse laser processing of transparent materials is crucial for the development of advanced industrial applications. Pump-probe diagnostics have proven to be a powerful tool for analyzing the laser matter interaction of spatially shaped beams with high temporal resolution. By extending this to broader range of temporal parameters of the pump, including flexible burst operation, combined with unlimited delay range of the probe and integrated optional polarization microscopy, high speed camera and observation during translation of the workpiece, the setup is suitable to analyze effects on different temporal and spatial scales in a single setup. The potential of this modular experimental system is demonstrated by analyzing multi pulse focusing of Gaussian and Bessel-like beams into glass.

We present a method based on simultaneous spatiotemporal focusing (SSTF) of the femtosecond laser pulses that enables to fabricate 3D structures on the centimeter scale. The isotropic spatial resolutions of fabrication have been achieved in different materials, making this approach easy to implement. For example, applying simultaneous spatiotemporal focusing (SSTF) of femtosecond laser pulses in two-photon polymerization (TPP) (i.e., termed as SSTF-TPP hereafter) uniquely allows for producing centimeter-scale 3D structures at a spatial resolution as high as ~10 μm. The fabrication resolution can be tuned simply by varying the power of femtosecond laser. The capacity of this SSTF-TPP method is confirmed by fabricating complex 3D structures such as Chinese guardian lions and a Terra Cotta Warrior. In addition, based on the SSTF scheme, we demonstrate 3D microprocessing in glass with a nearly invariant spatial resolution for a large range of penetration depth without any aberration correction. The SSTF technique can be useful for a broad range of superfine 3D printing applications such as micro-electromechanical systems (MEMS), infrared or Terahertz photonics, microfluidics, and 3D bio-printing.

In this paper, we will report recent progress on engineering various kinds of industrial scale laser micro-processing of PCB. FPC and glass materials used in mobile devices with ns, ps, and fs lasers, respectively. A full ps-laser processing solution of glass-based device (cover-glass, full-screen, and filter) was developed suitable for massive production. Similarly, a new processing strategy of FPC and PCB with new type of ns/ps-UV laser was also proposed for achieving good quality and high speed. Besides the well-known cutting and drilling, other processing such as coating removal using laser as an effective solution is also discussed here. In addition, the related industrialized processing modules and systems were developed.

Ultra-short pulse laser (UPL) industry is counting on high power P sources (100W class) to increase the throughput of a wide variety of industrial fabrication process. Nevertheless, this poses the challenge to overcome heat accumulation phenomena observed when P exceeds few tens of Watts compromising the machining quality. Novel beam engineering strategies are required to tackle this issue and guarantee high throughput with the high, distinctive, UPL machining quality. Here a study is reported on a variety of laser processes carried out with 100W class femtosecond lasers following two possible beam engineering strategies i.e. beam scanning with high speed (both a 100 m/s polygon scanner head and a 2D, 20 m/s fast, galvo-head) and parallel processing with multiple beams (obtained with both a DOE and an SLM head). Results show that by increasing P from few to 100 W also the throughput increases by nearly a factor 10 for micro-cutting (with galvo head and DOE) and even higher for surface texturing (with polygon scanner) while the machining quality is kept unchanged. Furthermore, we optimised the use of an SLM head for precise micro drilling of matrix holes showing the benefit of this technological approach in term of throughput. A full characterisation of the results carried out via optic and electronic microscopy will be also reported. We believe that all these results further increase the USP laser technology effectiveness level which is primed for industrial applications.

Publisher’s Note: This conference presentation, originally published on 4 March 2019, was withdrawn per author request.

Lithium-ion batteries applied for example in electric driven vehicles aim towards increased energy density at high active mass loading per unit area. Therefore, calendering processes are used to densify the electrodes. However, a low porosity, especially in top layer of the material compound, leads in general to a low rate (dis-) charging capability due to hindered lithium-ion diffusion. This work proposes a laser surface treatment method of highly densified cathodes to reduce the apparent process limitation of ion diffusion. The surface treatment is done with a short pulsed infrared laser in the nanosecond regime. Depending on the provided energy density in the laser spot the electrochemical inactive matrix of the cathode can be ablated partially and most of the pores below the top layer get reopened. Cathodes with different high densities after calendering are laser treated and electrochemically analyzed. Highly densified cathodes with a porosity of 20% exhibit a distinct improvement of rate capability at C-rates higher than 2C in relation to cathodes without laser treatment. Explicitly, at high current rates of 5C the electrodes of 20% porosity show an improved capacity of more than 20%. In addition, at low current rates the results show no negative impact of the laser treatment. The results lead to the interpretation, that selective laser ablation enables an improved access of Li-ions into the active mass of the cathode. Keywords: Li-ion battery, cathodes, selective laser ablation, rate

The confined and tailored interaction of ultrashort laser pulses with wide band-gap materials such as glass led to a broad range of applications and processing methods throughout recent years, especially for glass cutting. One major benefit of the short pulse duration is to locally modify a defined area inside of the glass volume. By stringing together numerous modifications along a desired contour, a preferential separation path can be created. However, complex contours and the extension to glasses of several millimeters thickness remain a challenging task due to the generation of cracks with undesired orientation, which antagonize the preferred separation direction. This might result in a loss of quality and stability due to rough cutting surfaces or even a lack of separability. A prominent example for single pass cutting profiles are Bessel-like beams. Their elongated but transversally confined intensity profile facilitate the homogeneous modification on a millimeter length-scale. Moreover, advanced beam shaping enables laterally anisotropic beam shapes leading to a preferential direction for crack propagation and allows to further increase the quality and process management. We employ pump-probe microscopy to study the effect of the interaction of single and multiple laser pulses. The combination of transmission microscopy, polarization microscopy and cutting processes under observation for time delays up to several microseconds allows the in situ detection of pressure waves and transient stress. Camera recording rates in the 100 kHz range allow the continuous detection of stress- and crack-formation and eliminate stochastic uncertainties. In combination with multipulse experiments and glass samples under feed rate, a profound understanding of cleaving applications is achieved.

Waveplates modify polarization by generating a phase change. Laser Induced Periodic Surface Structures (LIPSS) have recently started to be studied as waveplates due to the birefringence in-duced by the nanoripples, easily fabricated in a one-step process by laser, where LIPSS morphology is defined by the characteristics of the laser process parameters and the substrate material. The optical properties of these waveplates are defined by LIPSS parameters such as period, depth or width of the ripples. In this work we have deposited thin film coatings on stainless steel samples containing LIPSS for different coating thickness and composition. Results show that thin film coatings are a good candidate for the tunability of LIPSS birefringence since the coating modifies the induced polarization change and reflectivity of the sample depending on coating thickness and composition, as expected from numerical simulations.

CO2 glass ablation technology provides a very high degree of flexibility in the design of optical fiber sensors and optical probes for medical, sensing and industrial applications. In this paper, we review fabrication techniques for the design and manufacture of such devices, including diffusers, lensed fibers and cladding light strippers. We present an experimental characterization of the optical performance as well as a detailed description of the fabrication process for these devices.

Silicon and GaAs are typical materials used in terahertz components because of their high transparency and low dispersion, but their high refractive indices will cause about 30% reflection loss in power. Fabricating gradient index photonic structures (also known as moth-eye structure) on the surface of components have been examined suitable especially to terahertz system. In order to achieve high performance on anti-reflection in these structures, the gradient profile of refractive index, this is, the shape of tapers is important as well as high aspect ratio (= depth/pitch in tapers). We theoretically calculated anti-reflection characteristics of tapered structures with different refractive index taper profiles of Klopfenstein, linear and exponential, and the results showed that the Klopfenstein taper profile has the best performance on anti-reflection at the THz frequencies. Moreover, Femtosecond laser is reported as a strong method to perform microfabrication on Silicon substrate. However, if femtosecond pulses are continuously irradiated to the same point, the ablated material will absorb the incident pulse again, and reattach to the original point, which hindered the obtaining of high aspect ratio and shape control of the taper. By increasing the scan speed of laser beam, we decreased the pulse number continuously irradiated in unit time to reduce the thermal influence, and obtain a higher aspect ratio and smooth surface of the tapers. We employed femtosecond laser processing to fabricate anti-reflective structures formed by periodic tapers with different pitches. We also evaluated their anti-reflection characteristics experimentally and theoretically at terahertz frequencies (0.1 THz ~ 2 THz). The experimental results showed that the Fresnel reflection is almost decreased to zero at a wider frequency band, and the measured frequency dependence of reflection in the grating structures is good agreement with theoretical ones. These results showed that the laser processing is very useful to fabricate anti-reflection structures with precise dimensions.

Recent years have seen an increase in the demand of laser processing of transparent materials because of the numerous applications, such as the formation of through-silicon vias, glass scribing, the creation of optical wave guides, and so on. Furthermore, laser processing is expected to be used for fabricating photonic devices and circuits. Although significant research efforts have focused on laser processing of transparent materials, many unexplained mechanisms remain to be elucidated. In particular, mechanisms that remain unclear include plasma absorption and the process whereby traces expand when using double pulses. In 2017, to improve the laser-processing speed and efficiency, we proposed a method for cutting transparent materials called the “double-pulse explosion drilling method,” which uses two laser pulses of differing wavelengths to create internal modifications in a material. In the present study, we use the double-pulse method to drill through transparent materials and investigate how the second pulse affects laser-beam absorption and the generation of processing traces. We used a picosecond laser with pulses at 532 and 1064 nm for the first and second pulse, respectively. The target material was fused silica glass. The results clarify how the use of double pulses improves the processing efficiency. This presentation gives the experimental results and discusses the processing mechanisms at work in the double-pulse method.

CEA designs, studies and manufactures targets dedicated to laser experiments on the MegaJoule laser facility. These centimetric experimental objects are the place of laser/matter interactions: their designs are continuously evolving and combine many different materials and with various geometries. Their manufacturing requires high versatile and accurate level means. Among these technologies, laser micromachining means have been developed – namely based on excimer or femtosecond lasers. They combine the unique capacity to process many different materials with an outstanding precision and a small affected zone. In this study, we report experimental data related to tantalum oxide aerogel (Ta₂O₅) samples – low density material of interest for laser/matter experiments. This work aimed to get a first set of operating parameters for deep static drilling. In that goal we used different kind of laser sources: 193 nm excimer laser, Ti:Sa or Ytterbiumbased femtosecond lasers. Various parameters have been explored like fluence, wavelength, pulse duration and are related to ablation rates.

We report on the experimental and theoretical studies of ultrafast laser-induced optical breakdown on the surface of fused silica to elucidate the mechanism of damage formation and sub-optical-cycle dynamics in material processing using single and a burst of two femtosecond laser pulses. Ionization pathways, including photo-ionization (PI) and avalanche ionization (AI), are investigated by using single-beam and double-beam laser damage threshold measurements, which are used to analyze electron dynamics and extract the avalanche coefficient. The relationship between damage size and laser fluence is interpreted as a result of a combination of PI and AI. Electrical field rather than laser intensity is the fundamental influential factor in PI, and AI is found to play a significant role in creating the free electron density needed for optical breakdown. These findings are verified by a double-pulse delay-scan experiment where two cross-polarized pulses are used to induce damage with delay within a few optical cycles. Variation of the damage diameter is observed within one optical cycle, which is explained by the periodic change of polarization in the combined electric field. This finding shows the potential of controlling laser induced damage by tuning the temporal overlap of a burst of ultrashort laser pulses.