This PDF file contains the front matter associated with SPIE Proceedings Volume 11988, including the Title Page, Copyright information, Table of Contents, and Conference Committee listings.

Laser-microtextured surfaces have gained an increasing interest due to their enormous spectrum of applications and industrial scalability. In this frame, several research studies have demonstrated how laser-based fabrication methods can be used to produce functional surfaces. Furthermore, it has been demonstrated is many cases, that the combination of structures with feature sizes in different ranges (e.g., microelements decorated with nanostructures) can not only further enhanced specific functions but also to provide surfaces with several functionalities. In this context, this study summarizes how Direct Laser Interference Patterning (DLIP), Direct Laser Writing (DLW) and Laser Induced Periodic Surface Structures (LIPSS) can be combined, reaching advanced functionalities on technological relevant materials. The utilization of replication methods is also introduced, allowing to process for instance polymer foils. Finally, different surface functionalities are addressed, including wettability, ice-repellency, self-cleaning, antibacterial performance as well as enhancing optical properties of polymer materials for the fabrication of solar cells and organic light emitting diodes (OLEDs).

Femtosecond laser irradiation allows to modify the optical properties of transparent materials with high accuracy. In many applications, optical scattering produced by the laser irradiation is one of the major limiting factors. However, there are situations when the scattering is responsible for the basic principle of operation of the optical element. This report reviews two research directions where laser-induced scattering can be successfully exploited. First, spectroscopic measurements can be performed by analyzing the speckle patterns created by the scattering medium. The measurements are made possible by the strong dependence of the speckle pattern on the wavelength of light. A scattering chip created thanks to a femtosecond laser makes allows addressing the stability problem faced by many scattering spectrometers. The volumetric scattering centers are induced in silica substrate via micro-explosions caused by the focused laser beam. Such a spectrometer can be successfully used for interrogating fiber Bragg gratings or interferometers. Second example is found in optical reflectometry. This technology allows turning an optical fiber into a distributed microphone or thermometer. A single optical fiber can monitor a stretch of several tens of kilometers with an accuracy of several meters. Such systems have wide range of applications in civil engineering, geosciences and other fields. Reflectometry measurements are performed by observing the back-scattered light produced by the glass medium of the optical fiber. Femtosecond laser writing allows effectively increase backscattered light whilst introducing minimal additional losses. In this way, the sensitivity of reflectometric systems can be increased or their range can be extended.

Glass sheets with ~ 0.1 mm thickness are a promising material from which interposers for high density chip packaging can be produced due to its electrical and mechanical properties. For successful application in microelectronics, it is necessary to develop a way of efficient, high-speed production of interconnecting holes through such glass substrate, socalled through glass vias (TGVs). One of the most promising technique is Laser-Induced Deep Etching (LIDE), where picosecond laser is used to modified particular areas on the glass substrate. Then, using wet etching process, the area exposed to the laser will be etched more quickly than unexposed area. However, effective and large-scale glass modification often requires use of high-energy pulsed UV laser source, which unnecessary complicates the whole application. Here we present effective preparation of treated glass substrate using Yb:YAG laser at its fundamental wavelength 1030 nm, which is capable to overcome such disadvantage. We induced 5-15 m diameter regular affected areas on ~100 m substrate at various pitch, enabling scaled-up production of precise TGVs.

The fast-growing market for consumer-devices based on Augmented Reality (AR) technology requires optical waveguides. These components, which are used for image projection, are made of high-index glass or other transparent materials. Cutting eyeglasses out of the bare or preprocessed material has complex requirements for today’s available processes. For some years now, laser-cutting processes of transparent materials with ultrashort pulse (USP) lasers have been increasingly adopted in those industrial applications. The ability of a fully automated process flow is of critical importance, especially for AR products, which target the mass production market. Laser cutting tools combine good edge quality with fully automated process flows and free-form capability. This presentation covers the advantages of laser technology based on application examples for AR waveguides

Femtosecond laser material ablation in the GHz-burst mode has attracted much attention in the last few years and was controversially discussed. The crucial parameters determining whether the burst mode is beneficial or detrimental for the ablation efficiency are the number of pulses within a burst and thus, the burst length, as well as the energy of the pulses within the burst. In this contribution, we show new possibilities of femtosecond GHz-burst laser processing for top-down percussion drilling in alkali-free alumina-borosilicate. We show that deep high-quality holes can be drilled, however the inter-burst repetition rate is limited due to heat accumulation. Furthermore, we present time-resolved in-situ imaging of the drilling process. As laser source, a 100 W average power industrial femtosecond laser is used with a GHz oscillator. Thanks to its flexibility, this source allows for optimizing many process parameters such as burst energy, number of pulses within the burst and burst repetition rate.

Direct laser interference patterning (DLIP) has emerged as a versatile tool for producing well-defined microstructures that mimic natural surfaces with the aim of obtaining functionalized surfaces on relevant technological materials. On the other hand, the fabrication of surface patterns with micro- and submicron resolution features necessitates of advanced monitoring and setup strategies in order to ensure repeatability as well as quality control. In addition, the monitoring systems also allow inline capabilities to enable a closed-loop control approach. A possible strategy, that has been already applied to different laser processes, is the utilization of the sound pressure generated by the laser beam hitting the surface and producing ablation that can be detected and analyzed using commercially available microphones. In this frame, this work focuses on the analysis of the acoustic information extracted from the audio signal for determining process-inherent characteristics in DLIP, allowing the calculation of interference volume using stainless steel and titanium as reference materials. The results show that the acoustic emission measured at the ablation spot can be correlated to the interference volume shape and thus allowing to approximate the size of the interference spot. The possible utilization of this approach as an auto-focus and auto-setup method during DLIP is discussed.

In this paper, we report on the findings that pertain to evaluating the immediate viability of an UV-fiber-laserbased Si crystallization method referred to as spot-beam annealing (SBA). The SBA method leverages ultra-high frequency/low-energy pulses in order to flexibly create optimal conditions for executing various crystallization and annealing techniques for display and semiconductor applications. Specifically, we present recent experimental results that were obtained using a newly constructed SBA system that definitively show that SBA is capable of providing a highly ordered polycrystalline material, which is equivalent to the material generated using stateof-the-art ELA manufacturing systems. We discuss the implication of the results on the effectiveness of the polygon-scanner-based beam delivery schemes, and additional future variations and applications of the SBA method.

In this paper, we show via transient thermal analysis that the use of ultra-high-frequency high-power fiber lasers as implemented in the spot-beam annealing method makes it possible to (1) flexibly induce and mimic the overall annealing conditions that were accomplished previously using various other types of lasers, and (2) engineer and leverage the periodic and highly transient thermal spikes that arise due to the individual laser pulses. We point out and discuss how such annealing characteristics may be well-suited for optimally inducing structural/topological relaxation and compositional short-range ordering of amorphous thin films, as for instance are presumably involved in annealing of amorphous IGZO films on high-temperature-processing-intolerant glass/plastic substrates for fabricating stable oxide TFTs for AMOLED displays.

Laser-induced forward transfer (LIFT) is a 3D micro-fabrication tool wherein laser pulses are used to sequentially print thin sub-voxels of metal onto a substrate. We are developing a LIFT-based process to fabricate micron-scale parts with shape memory alloy (SMA) properties exploiting its high degree of spatial and temporal control. SMAs exhibit shape memory effect; during which they generate a substantial amount of strain or force, and hence can be used as the basis of actuators such as micro-grippers and fibre-optic manipulators, for surgical and other in-vivo medical applications. We are particularly interested in nickel-titanium (NiTi) SMAs given their biocompatibility and a transition temperature (the temperature at which the material returns to its initial state) close to body temperature. Small variations in chemical composition can be used to tune their transition temperature. However, compositional, and spatial control of these SMAs is limited to macroscopic manufacturing techniques. In this paper, we explore a novel approach to locally control the composition of NiTi alloy using LIFT. The donor is a multilayer comprising nickel and titanium thin films. During the transfer, the laser pulse melts and diffuses the metals forming a composite droplet. We demonstrate the possibility of obtaining NiTi deposits with equiatomic composition (50- 50 atomic %). Conventional SMAs have a narrow range of control parameters which makes it difficult for actuator design. However, by locally altering the composition, it would be feasible to locally tune the transformation window, providing a more complex response to temperature and hence a wide range of SMA based micro-actuator applications.

Laser-Induced Forward Transfer (LIFT) is a versatile technique, allowing the transfer of a wide range of materials, with no contact, and high accuracy. Here we show a complete study on the deposition by LIFT, focusing on the deposition of a high viscosity silver paste, from the LIFT process parametrization to the metallization and characterization of heterojunction silicon solar cells.

Since the demonstration of Davis et al. in 1996, femtosecond laser direct inscription emerged as a powerful tool for the fabrication of three-dimensional photonic circuits. Even today, the performance of calculations based on the volume density of components would greatly benefit from the 3D capability of fs-laser inscription. Although several advanced 3D devices such as photonic quantum circuits and lab-on-a-chip were successfully fabricated, compactness is still limited by the minimum achievable waveguide bend radius. Another growing interest is the laser inscription in materials with transmission up to the mid- and long-wave infrared for applications such as micro-organism detection, environmental monitoring, medical diagnostic and optical communication in the second atmospheric window at 8–12 microns. In this spectral band, materials that can be drawn into fiber optics, such as fluoride and chalcogenide glasses, are expensive and fragile. On the other hand, laser inscription allows the fabrication of waveguides in virtually any material, even crystals, enabling new IR applications, especially for harsh environmental conditions. In this communication, we present our recent progress on these two topics. First, we demonstrate waveguide bend radii down to <400 µm, which is an important improvement over the minimum 10-mm radius reported previously. The high refractive index change allowing such tight bends is attributed to a femtosecond laser induced band gap shift (FLIBGS) in the material. We also report low loss depressed-cladding waveguide (DCW) in crystals for IR applications. We particularly demonstrate the challenging inscription of a large DCW for single-mode operation at 10.6 µm with propagation loss of <0.63 dB/cm. We also describe a technique using a cover slide with optical contact to inscribe waveguides at the bulk surface for refractometric sensing applications.

Multi-focal beam shaping can enhance laser processing throughput by increasing the number of processing sites and lowering processing time. This paper implements multi-focal beam shaping by adopting a tunable acoustic gradient of index (TAG) lens, which scans the focal position in the axial direction at 140 kHz. When the laser is synced with the corresponding phases of the TAG lens, multiple focal spots can be selected, allowing for ultrafast and flexible multi-focal modulation without physically moving any optics. We further characterize the tuning parameters of the TAG lens, such as its frequency, amplitude, and phase, and demonstrate the dual-focal marking on both sides of a glass slide in a single lateral scan.

This paper investigates the Digital Glass Forming process for depositing single-mode optical fiber for waveguiding. The process utilizes a CO2 laser to heat the fiber to deposit onto a quartz substrate. This paper studies the effects of the feed rate and substrate scan speed on the fiber morphology. The relationship between the process parameters on the optical transmission through the fiber. The results show that as the fiber deforms to create a good contact with the substrate, the fiber core becomes elliptical. This reduces the overall transmission through the fiber. The dependence of the transmission on the radius of curvature of the printed track is also measured along with a preliminary demonstration of coupling between adjacent fibers.

The material processing with a femtosecond double-pulse laser beam has been demonstrated since 1990s. Only a few papers have discussed the possibility of ablation suppression mechanism. The mechanism of laser ablation with the double pulse beam is still open question due to two pulses consist of same laser wavelength because it is difficult to distinguish between the effects of the first and second pulses. In this study, the ablation rate has been investigated for titanium with a two-color double-pulse laser beam in the delay time (Δt) from 0 to 600 ps. The double pulse laser beam consisted of 800 nm with 150 fs pulse and 400 nm with < 150 fs pulse in cross polarization. The fluence of the first pulse was kept above the ablation threshold, while the fluence of the second pulse was kept below the ablation threshold. The ablation rate was clearly suppressed at the delay time of Δt ~ 60 ps in case of second pulse of 400 nm. On the other hand, in case of second pulse of 800 nm, the ablation rate was suppressed at the delay time of Δt ~ 200 ps. The delay time was approximately three times difference for both irradiation case. The difference of the delay time might be suggested that the ablation rate was effectively suppressed when the expanding surface plasma produced by first laser pulse should be close to the critical density for the second laser pulse.

Laser welding, which has many advantages such as high-speed process, deep penetration, narrow weld width, remote control etc., has been industrial applied for several industries. The formation of molten pool, and the mechanism of spatters generation have not been sufficiently investigated. In this study, we performed bead-on-plate welding tests on SS304 plates using disk laser by changing atmosphere pressure. The laser welding was observed in real time using the glass transmission method, and the shape of the molten pool was observed. As a result, it was found that the length of the molten pool was a factor for spatter suppression.

A 100 W blue diode laser with an optical fiber having core diameter of 100 μm was developed and installed into blue diode laser metal deposition system (B-LMD), achieving at the laser intensity of 7.58 ×10⁴ W/cm², four times higher than that of previous B-LMD system. Pure copper has been widely applied for various industrial components such as heat exchangers, heat pipes, electro circuits and motors because of having excellent properties such as thermal conductivity and electrical conductivity. Besides the copper, expected to be used for handrails, doorknobs, and other parts, are touched by a large number of people in order to prevent from infectious diseases, because of having the excellent properties such as an antibacterial property and a virus inactivation property. However, copper is low strength to only about 40% as strong as stainless steel. In order to add a new function of virus inactivation property to the surface keeping the strength, it is necessary to develop a coating technology to form a pure copper layer on the surface. Thus, we have developed a multi-beam type laser metal deposition method with a high intensity blue diode laser which newly developed with an output power of 200W and with 100 μm core diameter of optical fiber. As a result, the power intensity reached 7.5 × 10⁵ W/cm², and a pure copper layer with a thickness of about 24 μm was formed at a processing speed of 200 mm/s.