This PDF file contains the front matter associated with SPIE Proceedings Volume 11267 including the Title Page, Copyright information, Table of Contents, Introduction, and Conference Committee listing.

A main field of application for USP lasers is the fabrication of high-precision microstructures by ablation of bulk material. In the last 10 years, the output power of USP laser systems increased from around 10 W to several 100 W. This enables the increase of productivity of USP laser ablation processes by more than one order of magnitude. So far there is a leak of appropriate strategies and optical system to overcome limits based on heat accumulation. In this contribution, ablation strategies for steel and silicon by using far more than 100 W is deduced and presented.

In this paper we introduce a novel method of making micro-waveguides on silicon surface by the use of the Zone Refining Method. We produce the melting zone by a laser beam focused on the surface of a doped silicon slab to create a melting spot on its surface. By moving the melt zone across the silicon sample we can write a path of higher index of refraction on the silicon. The depth and the width of the waveguide can be determined by the wavelength and the spot diameter of the laser, respectively. We demonstrate the production of 1X4 μm² channel on the silicon, by using 532 nm laser beam. This method can be applied in microelectronics for the manufacture of light waveguides on integrated optoelectronics ICs.

Laser processing of polymeric materials by means of 100-mW class QCL lasers with emission wavelength of 7.728 and 4.329 μm were examined. Polymeric materials show absorption bands based on transitions between vibronic levels in mid-infrared (MIR) wavelength. Since such absorption bands are very sharp, resonant conditions with laser wavelength are critical. Quantum cascade laser (QCL) is a promising laser source for mid-infrared laser processing; emission wavelength can be customized by changing the heterostructure. In this work, we have employed 100-mW class QCLs and applied for focused irradiation at several polymeric materials, polypropylene (PP), polycarbonate (PC), polyacetal (POM).

The recent developments in the field of large area, flexible and printed electronics have fueled substantial advancements in Laser Printing and Laser Sintering, which have been attracting interest over the past decade. Resulting applications, ranging from flexible displays and sensors, to biometric devices and healthcare, have already showcased transformational advantages in terms of form factor, weight and durability. In HiperLAM project, Laser-Induced Forward Transfer (LIFT), combined with high speed laser micro-sintering are employed, as digital microfabrication tools for the demonstration of fully functional RFID antennas and fingerprint sensors based on highly viscous Ag and Cu nanoparticle inks. Having previously successfully demonstrated complex structures, this work’s focus is on increasing the process throughput and yield by increasing the laser repetition rate (up to 40 kHz) and scanning speed (up to 2 m/s), without compromising reliability and resolution. In order to gain insight into the effects of the incremented repetition rate on the printing procedure, the latter was monitored in real time via a high-speed camera, able to acquire up to 540.000 fps, coupled to the setup. Examples of resulting structures comprise well-defined interdigitated and spiral micro-electrodes with post-sintering electrical resistivity lower than 5 x bulk Ag and 3 x bulk Cu. The aforementioned results validate the compatibility of laser based processing with the field of flexible RFID tags and OTFT based fingerprint sensors and foster the wider adoption of LIFT and laser micro-sintering technology for laboratory and industrial use.

Over the last decades, the use of non-linear absorption phenomena triggered by ultrafast laser exposure in dielectrics has been widely explored, essentially with the aim of fabricating elements for integrated optics - such as waveguides and gratings, or for fabricating three-dimensional parts - such as fluidics channels and structural elements. Here we will discuss how this peculiar laser-matter interaction also provides a means for tailoring a variety of physical properties in materials, including heat conductivity, thermal expansion, Young modulus and stress state surrounding laser-affected zones. The ability to tune physical properties of dielectrics in three dimensions not only opens up interesting perspectives for sophisticated functional devices, but also a means to elucidate key mechanisms of ultrafast non-ablative laser-matter interactions.

Nondiffracting beams are known for their long line of focus, which has various applications in laser materials processing. Zeroth order Bessel beam is usually generated with an axicon and has a distinct circular spatial spectra. The nature of higher order Bessel beams, elliptical and parabolic nondiffracting beams is also conical and their spatial spectra have their own azimuthal modulation. We study numerically and verify experimentally generation of vortical Bessel beams, their superpositions along with elliptical and parabolical beams using an axicon. Laser induced modifications in glasses for various durations and beam powers using generated pulsed beams are analyzed.

With the development of touch panel display the need to process thinner glass using Ultra-Short Pulse (USP) laser has increased. Beam shaping improves the process yield and quality but requires specific precautions when applied to USP laser due to high peak power and dispersion. Bessel beams improve the quality of glass drilling and cutting due to the extended depth of field. We present Bessel beam generation using a reflective off-axis axicon giving a more stable beam compatible with scanning system and with a profile closer to theory. The characteristics of the beam and of the processed glass are described.

Transferring a defined amount of material can have many advantages. In this work, laser-generated microstructures are inserted in plain flexographic printing form material using a femtosecond laser to control the wetting behavior. The results are transferred to a printing form, which is functionalized by inserting these microstructures in the material transferring areas. In this paper, different structures and their effect on the printing results are investigated. Through functionalization of the printing form, not only can the transferred amount of material be adjusted, but also the cross section shape of the printing result. Further, after laser processing and printing, the printing form shows no relevant wear or chemical instabilities.

The formation of laser-induced oxide layers on titanium surfaces has been widely investigated for coloring and marking applications. Complex titanium-based oxides exhibiting multiple phases can be achieved through laser patterning. Laser processing offers several advantages in that discrete areas can be modified leading to patterns with differing optical and electronic properties. To date, most research has focused on the formation and thickness control of TiO₂, a wide bandgap semiconductor (~ 3.2 eV), as a means to control coloration. However, for many applications, including photodetectors and photocatalysts, a semiconductor oxide with a narrow bandgap (< 1 eV) is preferred to allow for strong absorption into the mid-IR. Other oxides and sub-oxides such as Ti₂O₃ have been identified as a byproduct of laser surface processing. In addition to its narrow bandgap, bulk Ti₂O₃ offers the unique property of having a semiconductor-metal transition at around 150 – 200°C where resistivity switches over an order of magnitude. Because of these properties, we investigate the optimization of laser processing conditions using picosecond and femtosecond laser irradiation to form Ti₂O₃. The effect of laser fluence, scan speed, pulse frequency, and sample chamber pressure will be discussed. Additionally, Ti₂O₃ thin films were grown via pulsed laser deposition to study structural phase purity, where the effect of growth temperature on optical and electrical properties is explored.

Uncapped “naked” Au, Ag, and Pd nanoparticles were synthesized using femtosecond laser-induced reduction of salt precursors in aqueous solution. Focusing femtosecond laser pulses into water induces optical breakdown of the medium, producing a dense plasma containing reactive electrons and radicals that can reduce metal ions to neutral metal atoms, which coalesce into nanoparticles. Manipulating the plasma composition by changing the solution pH and adding radical scavengers was found to enable improved control over the nanoparticle size distributions. The synthesized Au and Pd nanoparticles are catalytically active towards the hydrogenation of 4-nitrophenol to 4-aminophenol and could potentially be used in further catalysis applications.

This study numerically investigates energy generation on an array of nanoparticles on a flat surface subject to a laser beam in a TM mode. A systematical investigation of heating of an array of nanoparticles on a surface is essentially required to understand 3-D printing and different types of plasma processing and nanotechnology. The results show that electromagnetic wave propagating along the boundary on which nanoparticles rest leads to a distributed energy input. The effects of laser characteristics and arrangement of nanoparticles on distributed energy input are presented.

Self-organized structures like cavities and LIPSS are often used to generate specials surface functionalities with ultrashort pulsed laser machining. For a better understanding of the formation of cavities and LIPSS we performed a layer by layer surface visualizations on single crystal iron with different specific lattice orientations. The experiments indicate that formation and grow rate of cavities depends on the orientation of the crystal lattice. Based on this information we have been able to predict the cavity formation for given fluence on an electrical steel sheet with non-oriented grains with an accuracy better than 90% by analyzing the lattice orientations of the grains by a previous EBSD measurement.

This work presents results on laser texturing of aluminum-doped zinc oxide (ZnO:Al) films, a transparent conductive oxide (TCO), for improving light management in thin-film solar cells. Surface texturing is a fundamental step in solar cell manufacturing, especially in thin-film technologies, in order to decrease surface reflectance and enhance light scattering to improve light absorption in the PV absorbent. The ZnO:Al films used in this work were deposited by RF magnetron sputtering on glass substrates, and we used a Diode Pumped Solid State (DPSS) laser source emitting at 355 nm for texturing. All textures were obtained using a direct scribing technique and two different geometrical approaches for patterning were tested: The first consists in a simple linear pattern of equally-spaced parallel grooves while the second approach defines a crisscross pattern obtained by performing a second array of laser scribes orthogonal to the one defined in the first approach. We discuss the results attending at the morphological, optical and electrical characteristics of the samples, measuring the haze behavior and discussing the contribution of two possible scattering sources: The welldefined geometrical pattern formed by the grooves, acting as a diffraction grating, and a random roughness of low amplitude created during the laser process. Finally we deposited amorphous silicon solar cells onto the textured ZnO:Al films and studied the effect in the spectral response and short-circuit current (Jsc). We found, with the appropriate process parameters, an increment of 15% in Jsc compared to non-textured solar cells.

In the field of micro- and nanostructuring multibeam ultrashort pulsed laser processing attracts increasing attention due to its ability to generate periodic pattern like filters with a processing speed of up to 22.000 holes/sec. The multibeamscanner (MBS) developed at the Fraunhofer Institute for Laser Technology ILT enables laser processing with > 200 beams in parallel and a precision of < 1 μm. The MBS combines the latest femtosecond laser technology with a sophisticated optical concept. High precision multibeam processing is a useful approach to increase the productivity in laser material processing by means of ultrashort pulsed (USP) laser radiation. The developed multibeamscanner is capable of drilling holes with extremely small outlet diameters (< 1μm) into various materials with a customized arrangement and a density of more than 10.000 holes per mm². These holes can also be shaped according to customer requirements. Thus, this technology has become relevant for applications in the fields of consumer electronics, filtration, pharma and biotech industry. In addition to the various applications in terms of microfilter fabrication, the aim of this paper is to show the versatile use for structuring any 2.5 dimensional geometry on flat workpieces and to demonstrate the current and future possibilities of a multiscale simulation. To predict the ablation shape, temperature distribution and distortion in a multibeam processing, a detailed simulation of the physical processes during and after the laser ablation is required. A multiscale model to simulate the processing of larger workpieces is developed involving the interaction of multiple beams. Thereby, an increase in productivity by maintaining high process quality can be possible by a strongly parallelized USP laser process ¹.

The upscaling of laser micromachining processes with ultrashort pulses is limited due to heat accumulation and shielding effects. Multibeam scanning represents one of the strategies to overcome this drawback. It is in general realized by combining a diffractive beam splitter with a galvanometer scanner. A full synchronization with the laser repetition rate offers new possibilities with minimum thermal impact. We will demonstrate this by means of a multipulse-drilling on the fly process with a regular 5x5 spot pattern having a spot to spot spacing of 160µm. With a constant speed (synchronized to the laser) this pattern can be moved by exactly this spacing between two laser pulses. At a repetition rate of 100 kHz and an average power of 16 W we were able to drill more than 1'500 holes/s in a 10µm thick steel foil without any thermal impact. In a next step we will extend this technology with an SLM to different periodic patterns.

Drilling processes by ultrashort laser pulses meet the demand for high-end applications in the display and electronics industry. Especially the manufacturing of microstructures requires highest accuracy and minimal damage of the workpiece. A variety of applications, like the production of blind holes in multi-layer stacks or through holes in metal foils demand specific processing constraints. For example, applications like fine metal mask (FMM) require exact rectangular hole shape as well as tailored taper angles and minimized residual particle contamination. In large scale production environments, the total throughput also becomes decisive. To achieve these challenging needs, the spatial and temporal energy deposition are crucial parameters. In this context, beam shaping offers unique potential for controlling and scaling these micromachining processes. To pursue this approach, we present a novel adaptive beam shaping setup combined with a flexible TRUMPF TruMicro femtosecond laser. Our investigations target percussion drilling applications with various intensity distributions. We discuss methods for process optimization by controlling the spatial and temporal energy deposition. This enables us to analyze the correlation between micromachining results and the tailored absorption. Our investigations aim on shaping several beam properties like phase, amplitude, polarization and propagation characteristics using a liquid-crystal-on-silicon-spatial-light-modulator (LCOS-SLM). By correcting aberrations with a closed-loop setup, we generate robust process specific top-hat like intensity distributions.

The pulse duration dependence and inter pulse separation of pulse sequences influence on the energy specific ablation volume are still today open questions in laser material processing. The complete timescales for the processes involved in laser ablation can be visualized from the initial pulse absorption to the material removal occurring on a microsecond time scale by using an pump-probe microscopy method. Here we present time-resolved and energetic studies of the surface dynamics of the laser ablation processes on aluminium, copper and stainless steel bulk materials, which were analysed for pulse durations ranging from 500 fs to 20 ps, while keeping all other laser parameters constant. Our results indicate that the ablation process should be initiated by pulse durations shorter than the mechanical relaxation time of 3 ps and remain uninterrupted until the final state is reached after about 1 µs.

Bursts of 230 fs pulses with up to 25 pulses having a time spacing of 180 ps were applied to steel AISI304, copper DHP, brass and silicon in real surface texturing (milling) application by machining squares. The previously reported very high removal rates for GHz bursts could not be confirmed, on the contrary, the specific removal rate tremendously drops down to less than 10% for the metals and 25% for silicon when the number of pulses per burst is increased. This drop is fully in line with shielding effects already observed in case of MHz pulses and double pulse experiments. The increase of the number of pulses per burst directly goes with strongly increased melting effects which are assumed to additionally re-fill the already machined areas in this milling application. Calorimetric experiments show an increasing residual heat with higher number of pulses per burst. Further the removal rates of the GHz bursts directly follow the tendency of single pulses of identical duration. This fosters the hypothesis that in case of metals and silicon only melting and melt ejection lead to the high reported removal rates for GHz bursts in punching applications and that no additional "ablation cooling" effect is taking place.

Ultrashort laser pulses are already widely used in material processing due to high flexibility and precision. However, competition in industrial applications demands growth of processing efficiency every year. In our previous works, the laser ablation efficiency versus various conventional processing parameters like laser fluence, beam scanning speed, pulse repetition rate and hatch distance was studied and beam-size-optimization was introduced. Also burst mode processing was applied, since it attracted a lot of attention by scientific and technological communities. The purpose of our current work was to investigate the real advantage of the burst regime by comparing the beam-size-optimized single-pulse regime with the beam-size-optimized multiple-pulse burst regime, which was never previously demonstrated. The optimization was done by increasing the spot size to find the maximum ablation efficiency for various pulse numbers per burst and various pulse durations.

Ultrafast micromachining has found broad applications in a variety of scientific and industrial fields. Different materials and competing customer requirements (surface quality vs. processing speed vs. surface structure etc.) call for parameter studies prior to volume production as well as pulse parameter flexibility during operation. Up to now, often a nonoptimized point of operation for either best speed or quality had to be chosen due to limited laser source flexibility. TruMicro Series 2000 introduces true inter- and intra-process flexibility for pulse parameters such as pulse duration, pulse energy and pulse spacing up to GHz bursts. As of now, switching the pulse duration is possible within 300 fs and 20 ps in less than 600 ms without affecting beam pointing or energy stability. Therefore, intra-process pulse parameter changes allow maximization of the ablation-volume efficiency in one step and surface-quality optimization in a second, finalizing step. Additionally, inter-process pulse parameter changes enable material changes in between workpieces. In this contribution, we show how this novel flexibility for the first time leads to comprehensive and automated parameter studies that allow for next-generation process understanding and the clear selection of enhanced points of operation. We demonstrate how ablation of various materials can be increased by employing bursts on a nanosecond timescale where a simple increase in fluence would result in cone-like protrusions. Choosing the suitable timescale for energy deposition can either maximize energy efficiency of ablation or optimize ablation quality. With the TruMicro Series 2000, both optima can be combined to one efficient, high-quality process.

The extreme intensity of femtosecond laser pulses can enable microfabrication in glass. However, conventional femtosecond laser based glass processing has two severe limitations, viz., a low processing speed and the generation of damage during processing. To create a hole with a diameter of 10 m and a depth of over 100 μm using the conventional method, hundreds of pulses must be focused on a single spot because the volume removed by a single femtosecond laser pulse is too small. Furthermore, whenever a laser pulse is focused on the target surface, a strong stress wave is generated, thereby hindering precision. We have resolved these issues by coaxially focusing a single femtosecond laser pulse and a fiber laser pulse having a wavelength that is transparent to glass. A hole with a diameter of 10 μm and a depth of 133 μm was created in 40 μs, which indicates that the processing speed was over 5000 times faster than that of a conventional femtosecond laser. Moreover, the damage generated was considerably eliminated in comparison with the conventional method, and precision processing was achieved. The results of this study will help expand the industrial applications of femtosecond laser processing.

This article summarizes laser assisted single point diamond turning (SPDT) of select brittle and hard materials, using the μ-LAM process. These materials all have significant industrial importance in the modern day. It is shown that the μ-LAM process can produce smooth surfaces, with roughness values range from 40 nm RMS down to subnanometer RMS.

Laser ablation with ultrashort pulses allows to create precise and flexible geometries on various materials. However, the generation of complex surface geometries with low surface roughness, high contour accuracy and defined depth still represents a challenge on porous and inhomogeneous materials such as additively manufactured parts or carbon fiberreinforced plastics (CFRP). In the present work, optical coherence tomography (OCT) was utilized for high-resolution optical distance measurement. The measurement beam of the OCT-based measurement system and the processing laser beam were superimposed with a dichroitic mirror. Combining both beams allowed online, time-resolved recording of the ablated depth during laser processing. The comparison of actual ablation depth with the target ablation depth was used to select areas that had to be processed in the subsequent pass. This closed-loop control of the ablation process was used to generate complex 3D geometries in stainless steel. Furthermore, the closed-loop controlled ablation was utilized for postprocessing of additively manufactured aluminum parts in order to remove support structures and to significantly reduce the surface roughness. Moreover, the OCT-based measurements allowed to determine the orientation of the fibers during controlled laser ablation of CFRP for layer-accurate laser ablation, which served as preparation for repairing damaged CFRP parts.

During a spot laser welding process, a correlation between the generated sound and the obtained welding characteristics can be observed by preliminary experimental studies. This paper aims at understanding and explaining this correlation through a numerical finite element approach. A thermal-hydraulic model predicting the size of the capillary and the melted zone has been coupled with a simplified model of the sound propagation in the surrounding air. Different assumptions are then discussed and validated by confronting the numerical predictions with experimental data.

In this paper we present a novel sub-system for synchronizing motion of the galvanometer-based scanner and the XY stage system using a compact single controller that is independent of XY stage type or manufacturer. This integration directly utilizes the stage’s encoder output to compensate its motion in real time. Better than 10μm accuracy is demonstrated with various application patterns.

Cancer metastasis is the process in which cancer cells developed in the primary tumor start to spread in the body through bloodstream or lymphatic systems and home in on secondary sites, where they may generate new tumors. At the first stage, individual cancer cells migrate through narrow confined nanometric spaces or channels of micrometric interstitial spaces. It is thus challenging to create synthetic environments that mimic in vivo characteristics, fabricating relevant biosystems along with imaging techniques for sub-cellular visualization in order to understand mechanism of cancer cell migration, in particular in confining environments. Femtosecond laser assisted chemical etching (FLAE) is a technology performing subtractive processing of glass in order to create 3D microfluidic structures embedded in a microchip with the micrometric feature size. We evaluate herein relevant glass platforms capable to offer both observation of collective cancer cells migration over long periods and individual visualization at unicellular and subcellular levels on the target cell. Glass microfluidic biochips with micrometric characteristics are first fabricated by FLAE, hosting in vivo like microenvironments. Then, by applying two photon polymerization one may generate biomimetic polymeric architectures with confining channels inside microchannels. The fabricated 3D glass nanofluidics is applied to observe behavior of cancer cell deformation and migration in narrow spaces, providing new findings.

Ultrafast laser glass processing is highly interesting for microelectronics and consumer electronics industries. Indeed, ultrafast laser technology has the unique capacity to produce a high-quality surface or bulk modification in dielectric transparent materials thank to nonlinear absorption. However, there is a need to improve both processing quality and throughput in order to meet the industry requirements. Beam shaping, performed by tuning spatial or temporal intensity profile, polarization, fluence, or any other laser parameters, is a smart and flexible technique to achieve this goal. This work is dealing with double fs-pulse laser irradiation of fused silica. Our purpose is to investigate the benefits and the drawbacks in using single and dual-wavelength double fs-pulse laser irradiation of fused silica. The influence of pulse-to-pulse delay (0 to 5 ps), pulse duration of the second pulse (1 ps to 25 ns) and fluence on both removal rate and optical transmission will be discussed.

There have been great inventions, discoveries and developments of sophisticated laser processes in the recent past, many with highly complex lasers and optical setups. In order to be able to successfully introduce these processes for industrial applications, laser processing tools have to reliably demonstrate high efficiencies and yields and achieve an attractive cost per part value. This requires the fundamental understanding of the laser-material interaction mechanisms and of the factors which can influence the process. The associated challenges and solutions for industry hardened tools for the processing of technical glass substrates with ultrashort lasers are presented.

Surface nano-texturing can play an important role for efficiency enhancement of light emission and absorption in optoelectronic devices through reduced surface reflection or enhanced broadband absorption. Periodic and uniform semiconductor nanostructures are highly applicable in bandgap tuning applications but are quite challenging to realize through conventional techniques. We present the fabrication of large area and uniform square lattice based periodic nanostructures with 300 - 400 nm spatial periodicity on a GaAs substrate using pulsed laser interference. Single pulses from a plane-polarized pulsed laser working at 355 nm with 20-50 mJ energy and 7 ns pulse duration are used in a conventional four beam interference geometry at an incidence angle of 36.3° to realize square lattice patterns on photoresist coated over the GaAs substrate. The optical properties of the proposed designs are studied using FDTD simulations and show more than 95% of electromagnetic energy trapping over a broad optical wavelength range. This semiconductor based nanostructuring technology can find applications in improving the efficiency of solar cells or light emitting devices.