This PDF file contains the front matter associated with SPIE Proceedings Volume 12408, including the Title Page, Copyright information, Table of Contents, and Conference Committee information.

Industrial molds used to manufacture new type of Fresnel lenses require significant control over the size and shape of the ablation grooves. In particular, for demanding patterns, the objective is to obtain asymmetrical triangular grooves of around 10-20 μm width, micromachined with an ultra-short pulse (USP) laser for a better quality. To obtain this ablation profile we use a specific triangular beam shape obtained thanks to a reflection beam-shaping module. The idea is to move and rotate this triangular shape to have one of the edges of the triangle on one side of the groove, and its opposite point on the other side. In order to have total control of the laser process, we have collected a large amount of data of laser parameters, beam profiles and ablated groove profiles. This database allows us, thanks to the use of a deep learning algorithm, to predict the ablation profile from a set of laser parameters and beam profile pictures used for machining. The use of an artificial intelligence algorithm is justified by the fact that, at such a low resolution and with femtosecond laser pulses, light-matter interactions become complex, in particular due to nonlinear effects, which make using simulations difficult. Our deep learning model has the particularity of being a ”hybrid” model using several types of data: laser parameters, curves and images. This allows the algorithm to have an overview of the process but also to give the end-user a very fine control.

The flexibility of new laser sources and process-monitoring enables new possibilities in laser-based production technology, for instance the combination of different laser processes with many adjustable parameters. The fusion of domain knowledge and probabilistic models in the form of hybrid models allows an efficient optimization of these processes with machine learning. This can be a key technology to realize self-learning laser-based universal machines in the future. The article discusses some examples where algorithm-based optimization, partly supported by hybrid models, can already greatly reduce the effort required to find suitable process parameters.

A bead on plate welding test of pure copper plate was conducted with a hybrid laser which combined a high-power infrared (IR) laser and a blue laser to achieve a deep penetration and spatter-less welding of pure copper. A 1.5 kW class IR laser which has the wavelength around 1000 nm and a 1.5 kW class blue diode laser which has the wavelength of 450 nm were used as a heat source. The IR laser and the blue diode laser were irradiated perpendicular to the sample at the angles of 0° and 45°, respectively. Each laser was focused onto 2 mm thick pure copper sample and combined on the surface of it as a hybrid laser. The hybrid laser was scanned on the sample at 100 mm/s varying the output power of the IR laser and the blue diode laser. While scanning the lasers, the dynamics of melt pool formation and the spatters were observed with a high-speed video camera. After laser irradiation, the cross-section of the sample was observed and the penetration depth of the bead was measured. As the results, it was found that the penetration depth of pure copper increased and the number of spatters generated per scanning length decreased with the increase of blue laser intensity. Also, it was clarified that the melt pool dynamics affects the amount of spatter generated during welding.

We demonstrate the direct fabrication of graphitic carbon on a biodegradable polymer composite by laser-induced graphitization and applied the structures for the electrode of metal-free biodegradable triboelectric nanogenerators (TENGs). The laser-induced graphitization of fully biodegradable composite sheets composed of alkaline lignin powder and poly(L-lactic acid) (PLLA) was realized. The fabricated TENGs generated electricity by contact with synthetic polymers and natural materials such as water and plant leaves, indicating their applicability for on-site power generation in the natural environment. The proposed method provides the facile fabrication of biodegradable devices and the development of sustainable power generation.

Fiber Bragg gratings are the most popular type of optical fiber sensor. However, its commercial use is frequently limited by high cost and complexity of the interrogation unit. Here, an interrogator based on a femtosecond laser written silica scattering chip is designed and implemented. Such device can directly reconstruct strain, from the scattering speckle patterns, with a resolution of 70 μϵ (microstrain) within the range of 180-700 μϵ, limited by the slippage of the fiber coating, with the potential to be reduced with the system improvements.

The demand for long-term data storage in the cloud grows continuously into the zettabytes. Operating at such scales requires a fundamental re-thinking of how we build large-scale storage systems to archive data in a sustainable and costeffective manner. In Project Silica, a storage technology for the cloud is being designed and developed from the media up by leveraging the recent progress in ultrafast laser nano-structuring of the transparent media. Together with the advances in reading, decoding and error correction processes, high-density and high-throughput multi-dimensional volumetric optical data writing is achieved, enabling successful end-to-end proof-of-concept demonstrations of the technology. With exceptional media longevity, this could transform archival cloud storage. Here we briefly discuss the development of the technology, key metrics for cost-efficient optical data storage at scale, and successful proof-ofconcept demonstrations.

The requirements on the resolution of direct laser structuring are constantly growing and are now firmly in the sub-μm range. However, strong focusing of a Gaussian beam near diffraction limit is accompanied by a very limited depth of focus, which leads to an extreme increase in process sensitivity. To overcome the problem of the short focal tolerance, nondiffracting Bessel beams can be applied providing a depth of field in the mm range while allowing the diameter of the central processing spot to be 1 μm. Features in this size range are needed, for instance, for printed electronics such as highresolution displays. Since the reduction of the focus diameter is coupled with a decrease in productivity, the process must be parallelized to set the foundation for the industrial exploitation of Bessel beam technology for the manufacture of embossing and printing tools. This contribution presents the optical setup of a laser structuring machine that works with four parallel Bessel beams. Each beamlet can be modulated individually to enable the flexible generation of arbitrary surface structures. Ablation results with structure sizes of 1 μm are presented. A strategy to estimate the position-dependent peak fluence has been developed based on CMOS images of the Bessel beam along the propagation. This knowledge about the fluence is particularly relevant to prevent ablation by side lobes and to transfer the experience from ultrafast laser ablation with conventional Gaussian beams to the Bessel beam processing. Furthermore, this paper presents a novel approach to lateral Bessel beam scanning for efficient machining of cylinders based on RF shifting in AOMs or AODs.

As communication networks move toward higher frequency bands, thin glass substrates are advancing toward industrial production in packaging and interconnect applications as high-frequency, low-loss materials. While current techniques for the formation of through glass vias (TGVs) allow for efficient drilling of <40 μm diameter holes, there are currently limited commercially viable options for smaller TGVs. Presented herein is a unique approach to forming high aspect ratio TGVs in 10-20 μs for 50 and 100 μm thick glass. This is accomplished by using a high-power quasi-continuous wave (QCW) laser with a simple Gaussian beam profile focusing scheme. Crucially, this approach is compatible with high bandwidth beam steering technologies, i.e., the combination of galvanometers and acousto-optic deflectors (AODs), allowing for simple scaling to industrially viable throughputs of tens of thousands of vias per second for high-density drill patterns. The TGVs have straight, smooth sidewalls, and high uniformity. Birefringence image microscopy is used to further assess the finer quality aspects of the TGVs formed; considerable residual stress embedded around the TGVs was found after laser drilling, which could cause cracking in subsequent process steps. It is demonstrated that the stress can be significantly reduced by either annealing the glass substrate after drilling or drilling at elevated temperatures to mitigate the embedded stress.

The use of glass wafers for optical and electronic device substrates requires a high-quality, high throughput dicing solution. The patented Corning® laser nanoPerforation process is well-established in multiple industrial applications for glass cutting. A key attribute is the homogeneous appearance of the side wall over the full thickness of the glass and its high edge quality with low chipping and high throughput performance. Combining this laser-based solution with the mechanical breaking technology by Dynatex provides a complete and scalable path for glass wafer dicing applicable to normal, as well as very small die sizes. Detailed investigations on several different glass wafer materials have demonstrated the current capabilities for this laser and mechanical singulation process and confirm the exceptional performance. A tiny die size of 150×150 μm is demonstrated on a 200 mm diameter, 150 μm thick glass wafer. The laser-based solution can be enhanced to ensure side-wall uniformity at the large number of intersecting lines found on densely packed wafers. Finally, the requirements of the clear aperture for the laser entrance can be reduced into the range below 100 μm by applying Corning’s fundamental process understanding and optimization of the laser optics.

Requirements on glass manufacturing with exceptionally high mechanical strength triggered development of new laserbased processing methods. Localized modifications produced by ultrashort pulsed lasers are attractive but may lead to micro-crack generation in glass. Aiming to control stresses during volumetric material modifications, we have studied the effect of pulse duration experimentally. Bessel beam shapes with arbitrary conical angles have been generated using a programmable spatial light modulator (SLM), while stresses have been monitored using time-resolved optical transmission and cross polarized microscopy. Pulse duration variation influences mechanical stress in the laser glass interaction, and we found the optimized pulse duration exists in the laser glass machining by pump-probe microscopy.

A two-step laser-based concept is presented for cleaving glass substrates with tailored edges. In a first step beam shaped ultrashort laser pulses are used to modify the transparent material along chamfered or C-shaped edges. Secondly, thermal stress is applied close to the modified area by absorbing the radiation from CO₂ laser. The tensile stress thus induced on the upper side of the glass leads to the actual release. The efficacy of our approach is demonstrated by presenting selected samples with tailored shaped edges and discussing corresponding edge qualities.

Laser-induced bubbles can be formed by focusing a conventional nanosecond (ns) laser in a liquid. We recently developed a microfabrication technique (microfabrication using laser-induced bubble (microFLIB)) and applied it to polydimethylsiloxane (PDMS), a thermoset polymer. The technique enabled the rapid fabrication of a high-quality microfluidic channel on a PDMS substrate and selective metallization of the channel via subsequent electroless plating. In addition, we found out that this technique enables true three-dimensional (3D) microfabrication of PDMS so that a hollow microfluidics can be embedded in the polymer substrate. Furthermore, a through hole having high aspect ratio of more than 200 can be fabricated by the single laser scanning. Therefore, in this presentation, we will introduce how the microFLIB works in detail and demonstrate surface microfabrication of PDMS and 3D microfabrication of hollow microstructures in PDMS. In the experiments, a ns laser beam was focused inside uncured liquid PDMS and was scanned to generate 2D and 3D line of laser-induced bubbles. In the microFLIB processing, the shape of the created bubbles was retained in the uncured PDMS for a while; thus, the line of bubbles generated by the laser scanning successfully produced a microfluidic channel on and inside the PDMS substrate after subsequent thermal curing. The developed microFLIB technique permits the high-speed and high-quality microfabrication of PDMS and can be applied to biochip applications.

Ultrashort-pulse micromachining has found a rising number of applications in numerous industrial and scientific fields. Modern ultrafast lasers like the TruMicro series enable a high degree of pulse parameter flexibility. Yet, this flexibility also brings challenges for optimization due to complexity with respect to endless parameter combinations. Unique laser features such as a fast tunable pulse duration, MHz- and GHz-bursts offer the possibility to address several machining challenges depending on the application. Even for a single application, useful pulse parameters are generally related to the particular process phase. For example, high ablation rates are commonly in contrast to highest surface qualities. In this contribution we focus on applications that benefit from multi-step processes with advanced successive parameter sequences, enabled by fast and controlled intra-process pulse parameter switching. As a result, multiple samples are demonstrated where highest processing speeds are enabled in combination with superior qualities and various surface finishes. Besides an optimized temporal energy deposition for a variety of applications, benefits of ultrafast processing with shorter wavelength, position synchronized output and an integrated hollow-core fiber delivery are demonstrated.

We report the experimental studies of UV laser ablation with a microspot scanning system comprising of a 10 ps, 355nm ultrashort pulse laser in combination with a standard galvoscanner employing a Microscan MSE-G2-UV extension from Pulsar Photonics. The UV wavelength provides the first step in downscaling the feature size and the microscan extension allows the laser beam to be tightly focused down to a very small diameter of < 1.5 μm. The small focal spot size allows highly precise ablation of microstructures. Laser ablation characteristics with the microscan objective is investigated in steel and copper for different laser repetition rates. The threshold fluence and the energy penetration depth for steel and copper were found to be comparable for repetition rates from 200 kHz-2 MHz. The advantages and also the limitations of laser ablation using the microscan objective is discussed, especially with respect to its small Rayleigh range of ~ 5 μm. The sample positioning tolerances and maximum achievable ablation depths count among the latter. Initial experiments on laser drilling in 10 μm steel foils is also reported, with the exit hole diameter of the order of the focused laser beam diameter.

Selective laser etching (SLE) has demonstrated to be an effective technique to push further the exploitation of laser-based surface functionalisation techniques allowing to reach always smaller surface structures at higher resolution and with controlled aspect-ratios. In this work, SLE is investigated on sapphire as a method to induce different surface functionalities such as antireflective effect and wettability modification. The effect of laser process parameters on the etching rate is evaluated in Gaussian and Bessel laser-beam configurations for KOH etching solution by means of scanning electron microscope (SEM) and confocal microscope analyses.

Recent experiments with newly developed radial machining paths have shown that process time gains of up to 300% can be achieved compared to conventional linear scanning strategies. Various radial patterns such as circles and spirals were analyzed and developed. These individual methods were further optimized to achieve the highest possible process speeds and reduce downtime when the laser is not in operation. Furthermore, an optical z-axis was integrated into the system, which allows the marking of workpieces with uneven surfaces while maintaining full synchronization between the scanner and the laser system.

In this work, we study the ablation dynamics of copper (Cu) induced by single fs pulse and fs GHz bursts using in situ multimodal diagnostics; time-resolved scattering imaging, emission imaging, and optical emission spectroscopy. Multimodal probing techniques reveal that fs GHz bursts rapidly remove molten liquid Cu from the irradiated spot due to the recoil pressure exerted by following fs pulses. Material ejection stops after burst irradiation due to the limited amount of remnant matter, combined with the suppressed heat conduction into the target material. Our work provides insights into the complex ablation mechanisms of GHz fs bursts, which are critical in selecting optimal laser conditions in cross-cutting processing and micro/nano-fabrication applications.

In nanosecond pulsed laser processing techniques such as laser annealing and laser doping, the surface temperature of the laser-irradiated area changes on a nanosecond scale, which strongly affects properties of the processed material. Therefore, a temperature measurement method with in-situ, non-contact, nanosecond time response and microscalespatial resolution is necessary to optimize the laser processing conditions. In this study, a two-dimensional temperature distribution on a Si wafer surface irradiated by a nanosecond pulsed laser was estimated by a two-color temperature method using an ICCD camera with nanosecond time resolution. 20 ns after the laser irradiation at 1.0 J/cm², the area above 1500 K started to appear in the two-dimensional temperature distribution. It is confirmed that the high temperature area increased further at 40 ns and was maintained for a certain period of time in temperature distribution. The average temperature at the center of the laser-irradiated area reached above 1685 K, which is the melting point of Si, at 40 ns and remained until 110 ns. The probe laser was irradiated to the laser irradiated area and the reflectivity was measured. The reflectivity varied according to the change between the solid and liquid phases on the Si surface, and the results corresponded to the two-dimensional temperature distribution.

Titanium (Ti) is widely used for biomaterials such as an implant for human body due to its excellent anti-corrosion. However, new functions should be added to Ti substrates because a strong revival is slow in a joint with a bone. A useful method is periodic nano structure formation on a material to control cell spreading and promote the osteogenic differentiation of cells. When a femtosecond laser is irradiated on a Ti plate at a fluence of near the ablation threshold, periodic nano structures are formed in the direction of perpendicular to the polarization angle of the laser pulse. In our previous study, it was found that the direction of cell was spread by periodic nano structures formed on Ti plate. For the controllability improvement of the cell spreading direction, it is required to improve the uniformity of periodic nano structures. Since the period of nano structures depend on the target material, irradiation fluence, number of irradiation-pulses, incidence angle, and laser wavelength, it is difficult to control the uniformity. In this study, to improve the uniformity of nano structures, Ti plate was irradiated by two-color double-pulse irradiation with a femtosecond laser at the wavelength of 800 nm. As the results, when the 800 nm and 400 nm pulses had orthogonal polarization directions, high uniformity of periodic nano structure was formed.

Laser welding in vacuum with a high-power laser is performed for a stainless steel plate which forms a keyhole inside the molten pool, resulting in a deep penetration without spatters. The spatter is one of the defect factors for laser welding, such as thinning of weld bead, and pore generation. In order to elucidate the mechanism of spatter free process, in situ observations were conducted to investigate dynamics of molten pool and keyhole in vacuum laser welding with a highspeed video camera and X ray transmission system. A stainless steel type 304 (SS304) is widely used in several industries such as automotive industry, chemical plants, petrochemical industry, etc. due to its excellent properties such as high corrosion resistance, hardness, low-temperature toughness, and thermal stability. The stainless steel type 304 (SS304) was set in a vacuum chamber and then a disk laser with an output power of 6 kW was irradiated and scanned on it to form a weld bead under aimed pressure. At the same time, the behavior of molten pool and keyhole were captured with real time observation system and an X ray transmission system, respectively. From the results, it was found that this fluctuation of molten pool affected the generation of spatter.

4H–Silicon carbide (4H-SiC), which is a wide-bandgap semiconductor, is a promising material for high-power, ecofriendly devices owing to its excellent material properties. For the fabrication of SiC power devices, low-resistance ohmic contact must be established at the metal–semiconductor interface, which requires high-concentration impurity doping. In this study, we successfully doped 4H-SiC with high-concentration nitrogen under excimer laser irradiation using SiNx films containing dopants on 4H-SiC. Results indicated that a contact resistance of 10−6 Ωcm2 was obtained. The effects of doping characteristics due to different laser parameters were also investigated.

This conference presentation was prepared for the Laser Applications in Microelectronic and Optoelectronic Manufacturing (LAMOM) XXVIII conference at SPIE LASE, 2023.

Laser-induced periodic surface structure (LIPSS) in nanometer scale formed by femtosecond (fs) laser pulses depends strongly on laser parameters such as fluence and superimposed pulse number, as well as the surface condition of target materials. Process control based on in-process monitoring is one of the solutions to form the nanostructure stably and homogeneously. However, it is difficult to monitor the nanostructure in the process, because it is much smaller than the light wavelength. This paper reports on a new technique for in-process monitoring of the periodic nanostructure using its anti-reflection property. As a target, we used a synthetic quartz plate. The linear-polarized 1030-nm, 250-fs laser pulses from a Yb fiber laser amplification system operated at a repetition rate of 20 kHz were focused with an objective lens and scanned on the target surface. Microscopic images of the target surface with coaxial epi-illumination and transillumination were acquired with two CMOS cameras. From these images, the surface reflectivity and transmittance were evaluated. After the ablation experiment, the surface morphology was observed with a scanning electron microscope. The surface of which transmittance increased as reflectivity decreased, had a line-like periodic nanostructure with a period of ~200 nm and a depth of ~1 μm. On the other hand, the surface of which both transmittance and reflectivity decreased did not have the nanostructure. These results demonstrate that an observation technique using anti-reflection property is much more effective in monitoring fs-laser-induced nanostructure on glass in the process.

In this paper, high-quality and high-speed laser soldering technology for Mini-LED backlighting for LCD display and fully automatic laser repair technology to remove attached tiny fault Mini-LED and attach a new good Mini-LED are introduced. For televisions or monitors, LCD Display technology has been quickly developed and saturated. And new OLED technology is now actively penetrating into this market. However, as an effort of extending LCD market and competing it against OLED quality, LCD technology is now accepting Mini-LED backlighting technology for local dimming applications. In this Mini-LED application, there are two technology huddles such as high-quality soldering and high throughput on ultra-thin flexible PCB. To meet these requirements, advanced soldering technology of LSR (Laser Selective Reflow) bonding technology is developed. LSR technology can make very good bolding quality including high-strength bonding with 1.5 to 2.0 times higher shear strength than conventional mass reflow technology and almost no PCB surface color change which is very important to generate complete black background when it is needed. To perform high-quality and high-speed laser reflow of more than ten-thousand Mini-LEDs on large size PCB substrate, 400mm long line beam using advanced flat-top optic and high-power laser were used. When fault Mini- LED chips are identified or wrong-position or wrong-gesture bonded Mini-LED chips are found, those Mini-LED chips should be repaired not to be throw out expensive whole finished backlight substrate with Mini-LEDs. For this purpose, very nice fully automatic laser repair technology is developed which is introduced in this presentation.