This PDF file contains the front matter associated with SPIE Proceedings Volume 12872, including the Title Page, Copyright information, Table of Contents, and Conference Committee information.

Generation of multiple parallel non-diffractive beams without any disruption of each beam is a challenging task. Here, we report the approach of spatial-spectral modulation for non-disruptive generation of Bessel beam array. Such modulation is realized with a simple beam splitter placed in a Fourier plane of the initial beam. The various designs of the beam-splitter phase mask allow to generate an array of the Bessel beams with various shapes and controlled intensity distribution without mutual interference of each beam. As such, this array formation can enhance quality of glass cutting and increase the throughput of micro-patterning of glass-fine mask required for a new generation high-resolution OLED display.

As Augmented Reality (AR) and Mixed Reality (MR) devices emerge and promise to revolutionize the way in which we perceive and interact with the world, the continued focus on the low-cost, high-volume manufacturing of the waveguides that underpin the technology is required. A significant challenge is the singulation of the high refractive index glass wafers into individual waveguides without affecting the sensitive optical components (e.g., gratings) on them. The laser nanoPerforation glass singulation process developed by Corning is well-established in multiple industrial applications and has been successfully deployed into high-volume manufacturing for AR waveguide devices. A detailed investigation into optimizing the edge strength of 0.5 mm thick Corning high refractive index glasses (n=1.7-2.0) reveals values in the range of 130-150 MPa (B₁₀). By applying fundamental process understanding and further optimization to Corning 0.3 mm Augmented Reality Systems (ARS) 2.0 glass, an initial demonstration of edge strength values up to 202 MPa (B₁₀) is realized.

This research advances the application of Laser-Induced Graphene (LIG) in pressure sensing and energy harvesting, focusing on LIG derived from fluorine-integrated colorless polyimide (CPI) films. The graphitization of CPI films using laser techniques, validated by ReaxFF simulations, creates a porous LIG structure ideal for high-sensitivity pressure sensors. The CPI-LIG pressure sensor demonstrates exceptional sensitivity (60.340 kPa^-1 at 1.0–1.5 kPa), quick response (27 ms), and fast recovery (36 ms), with proven accuracy in tracking human movements. Additionally, the CPI-LIG enhanced triboelectric nanogenerator (TENG) significantly boosts power output to 65.2 mW/m², a 650% increase over traditional LIG, under a 40 MΩ load. This study thus reveals novel applications of CPI-derived LIG in sensitive pressure sensors and efficient energy harvesters.

Interest in glass for Integrated Circuit (IC) packaging and interposer applications has accelerated in recent years, due to its favorable mechanical and electrical properties compared to current advanced materials. This report describes our recent results on Through Glass Via (TGV) drilling, utilizing a novel process employing a single laser source with an engineered pulse duration, pulse repetition frequency, and average power to rapidly form TGVs in 50 and 100 μm thick glass. The process forms TGVs with a ∼10 μm diameter with zero taper, smooth sidewalls and minimal splash; the dimensions of these TGVs meet the requirements for next-generation interposers to replace through silicon vias. Unlike Bessel beam-based processes, this process is compatible with high bandwidth beam steering technologies (galvanometers and Acousto-Optic Deflectors (AODs)), enabling an industrially viable throughput in high-density drill patterns of more than 10000 vias per second. The formation dynamics of the TGVs are elucidated using multiphase simulations and in-situ spectroscopic methods. Stress mitigation in the fully formed TGVs is explored through annealing studies; an alternate approach utilizes heating of the glass substrate during the laser processing to minimize stress formation during the drilling process. Both methods are shown to mitigate embedded stress and avoid cracking.

Simulations and measurements on selective laser etching of display glasses are reported. By means of a holographic 3D beam splitter, ultrashort laser pulses are focused inside the volume of a glass sample creating type III modifications along a specific trajectory like pearls on a string. Superimposed by a feed of the glass sample a full 3D area of modifications is achieved building the cornerstone for subsequent etch processes. Based on KOH the modifications are selectively etched at a much higher rate compared to unmodified regions resulting in a separation of the glass along the trajectory of modifications. For gaining further insight into the etch process, we perform simulations on this wet chemical process and compare it to our experimental results.

GaN-based wide bandgap transistors offer several advantages compared to silicon-based counterparts. These transistors are effective in reducing power conversion losses and find applications in various sectors, including power supplies in data centers and traction inverters for electric vehicles and other components empowering the renewable energy transformation. To fully harness the potential of GaN-based transistors, quick and reliable detachment from the growth (typically sapphire) substrate is essential. Separation avoids structural and electrical problems caused by low thermal and electrical conductivity of the growth substrate and enables flexible integration with materials that are optimal for the individual application. Furthermore, the limited scalability of sapphire substrates, attributed to handling difficulties and material costs, emphasizes the need for reliable detachment. While the conventional method employs nanosecond-pulsed excimer lasers that dissociates GaN to metallic Ga and N₂-gas, this work utilizes an ultra-short-pulsed deep UV laser operating at 266 nm wavelength, which allows for precise and localized energy deposition at the sapphire-GaN interface. Single pulse picosecond processing allows to minimize parasitic heat accumulation and thermal damage to preserve the integrity of underlying layers and surrounding structures. This contribution encompasses an analysis of the threshold for gallium formation and the level of damage to the surroundings. Furthermore, it investigates the influence of bonding materials on detachment performance and discusses limits of achievable throughput.

Silicon-based integrated photonics holds the promise of revolutionizing key technologies, such as telecommunications, computing, and lab-on-chip systems. One can achieve diverse functionalities in two ways: on the wafer surface ("on-chip") or within its bulk ("in-chip"), the latter gaining recognition due to recent advancements in laser lithography. Until recently, 3D in-chip laser writing has only been utilized for single-level devices, leaving a vast potential for monolithic and multilevel functionality within silicon untapped. In our previous research, we successfully designed and fabricated multilevel, high-efficiency diffraction gratings in silicon using nanosecond laser pulses. Their high performance stemmed from effective field enhancement at Talbot self-imaging planes. Our current work takes a theoretical approach, investigating how varying the grating period affects the performance of in-chip multilevel gratings. We demonstrate that the previously achieved 95% diffraction efficiency at a 1550 nm wavelength is also attainable with a reduced period of 3 μm. This smaller period is predicted to allow for spectral filtering, nearly equivalent to commercially available filters in terms of Full Width at Half Maximum (FWHM). Our findings underscore the potential of volumetric Si photonics and mark a significant step towards realizing 3D-integrated monolithic chips.

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. In the experiments, a ns laser beam was focused inside uncured liquid PDMS and was scanned to generate 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. However, mechanism of this process still remains unclear. Therefore, in this presentation, we will introduce how the microFLIB works in detail and investigate the behaviors of the bubble in the uncured PDMS and explore how the bubble connect to each other during the microFLIB using pump-probe imaging technique.

Pulsed lasers can be used to eject materials from transparent donors through an ablation-based expulsion mechanism. Laser Induced Forward Transfer (LIFT) is an approach based on expelling material from a donor towards a receiver. The method can be potentially exploited to develop multi-material deposition systems for producing freestanding products as well as hybrid manufacturing combined with other processes for microelectronics applications. The size of the ejected material depends on temporal and spatial interaction of the laser beam as well as the size of the donor material. The combined use of femtosecond pulses, UV wavelength, and nm-sized solid donors can allow to reduce the droplet size towards nm scale. Hence, this work shows the development of the system architecture and the process for the laser induced forward transfer of PVD produced pure titanium. The relationship between the laser related parameters, the formation of the droplets and different regimes were defined. Single droplets with sub-micrometer diameters and heights in nanometer range were successfully produced. The results are then used for developing a platform for 3D material deposition from nano to microscale dimensions to be used in microelectronic applications.

Currently the most widely graphene production technique is growth via Chemical Vapor Deposition (CVD) on copper thin films previously deposited by evaporation on sapphire substrates, which can yield high-quality monolayer graphene coatings. However, the transfer of graphene from the growth substrate via conventional methods making use of support/protective layers (e.g., organic polymers), lithographic masking layers and chemical etching, is a multi-step complex procedure. Here, we report the use of laser-based transfer technique, namely, Laser-Induced Forward Transfer (LIFT) for the reliable, reproducible and high-quality transfer of graphene pixels at designated areas on SiO₂/Si substrates, directly from the growth substrate. LIFT is an environmentally friendly, mask-less technique and offers high resolution with high throughput. The quality of the transferred films has been inspected via SEM, Raman spectroscopy, and AFM characterization. Electrical characterization for mobility measurement will also be performed. The aim of this study is the process optimization of LIFT process parameters, such as the laser fluence. The reported results highlight the advantages of the laser-based monolayer graphene deposition methods for the on-chip integration of graphene-based photodetectors.

Nanoparticles (NPs) are increasingly being used in various fields with numerous applications in photonics. Specifically, there is a growing interest in using rare-earth (Re) doped NPs as laser-active material in silica optical fibers, which can provide new and enhanced optical properties for, e.g., fiber lasers. The ReNPs are commonly prepared using chemical synthesis. Here, we present an investigation of synthesizing Yb:YVO4 NPs via pulsed laser ablation in liquid (PLAL) using a femtosecond laser. Processing conditions affect the size, structure and colloidal stability of the Yb:YVO4 NPs, producing ovoid-like and less aggregated spherical NPs in water and ammonia, respectively.

There is increased interest in ultrashort GHz burst pulses for uses in precise laser microfabrication. Whereas previous works have focused on GHz burst processing at fundamental wavelengths, here we present results for processing with the third harmonics generated from GHz burst pulses. We find that with these pulses, we are able to achieve high-quality microfabrication of silicon with markedly less debris than with traditional non-burst pulses. We then demonstrated debris-free milling of a silicon micro-hemisphere to show how these conditions are particularly favorable for feedback monitored fabrication applications. Such results show the benefits of GHz-burst-pumped third harmonic machining by commercially available laser sources.

PCB substrate size has been increased and its thickness has been decreased for cost reduction and integration of various functions in advanced semiconductor packaging and removing the humidity from the paste applied to large-area electrode of rechargeable battery has become important. To perform bonding processes for these substrates and semiconductor chips or remove the humidity from top surface to deep layer in the paste applied during making the electrode of Rechargeable Battery, the local heating using a large area flat-top laser beam is required. In this presentation, two types of large area flat-top beams obtained by plate-type cylindrical lens and VCSEL (Vertical-Cavity Surface Emitting Laser) based flat-top beams are compared and discussed. Several key characteristics such as beam uniformity, beam steepness, beam size variability, the power in the flat-top region and others are compared.

A pure copper layer was formed on the stainless-steel substrate with low-dilution layer by a Wire-based Laser Metal Deposition method (W-LMD) with a blue diode laser. Pure copper is an important material for realization of a carbon-neutral society because of excellent properties such as electrical and thermal conductivity. As the demand of copper increases, a wide variety of processing methods are required with high yields. Thus, the LMD method, which is one of the Additive Manufacturing (AM) technologies, is focus on this study. The W-LMD is the process in which a metal wire is fed to the laser irradiation point and melted and solidified to form a layer. Conventional W-LMD with near-infrared fiber laser has formed a layer of Fe-based alloy, Ti-based alloy, Ni-based alloy, and so on. However, it was difficult to form a pure copper layer since light absorption rate of copper in this region was less than 10%. Therefore, we focused on blue light at the wavelength 450 nm. It is because light absorption rate of copper in blue region is 60%. Thus, the high-power blue diode laser has been developed and installed the W-LMD system. In this study, the pure copper layer was tried to form on the SS304 substrate with our W-LMD system. As the results, copper layer was formed with a layer thickness of 388 μm and a dilution thickness of 22 μm at the output power of 500 W, stage sweep speed of 10 mm/s, and wire feeding rate of 10 mm/s.

A pure copper layer was produced on a stainless-steel type 304 substrate by using a multi-beam laser metal deposition method with blue diode lasers (B-LMD) to add the antibacterial and virus inactivation effect of pure copper on a high-strength and cost-efficient material. To make a copper layer on a substrate by LMD method, beads must be formed continuously at specific intervals and each fabricated bead must be overlapped on the substrate. In this study, to fabricate a high-quality copper layer on a SS304 substrate, the effect of hatching distance (distance between each bead) was investigated. The copper layer was fabricated on the SS304 substrate with a multi-beam B-LMD method at the spot size of 233 μm varying the hatching distance. After the copper coating process, the surface roughness and cross-section of the copper layer were observed. As a result, the surface roughness became high and a large amount of voids were formed inside the layer when the hatching distance was under 150 μm. On the other hand, dilution of copper and SS304 increased as the hatching distance increased.

We simulate laser ablation process of different metals in both ns and fs regime. Finite element method was implemented to numerically solve the thermal equations. Ablation has been modelled as a normal downwards mesh velocity. Ablation curves have been obtained for metals such as Ag, Cu and Al and oxides such as CuO; in ns regime we have also simulated multipulse operation. For ultrashort fs pulses, the Two-Temperature Model (TTM) needed to be applied. Improvements were made in an important thermal parameter of the TTM, the electron heat capacity, by solving the exact equations which give this parameter within the Free Electron Gas (FEG) model framework.