Ultrathin porous transport layers (PTL) were prepared by laser-perforation of titanium foils. The thickness of employed titanium foils ranged from 25 to 127 mu m. In the laser-based process, porous transport layers with controlled and regular patterns were created. The process involved the ablative fabrication of surface structures along with through-plane holes ranging from 10 to 100 mu m in size. The porous transport layers were designed with highly ordered patterns featuring micron-sized channels, which enhance their mass transport properties significantly. Laser-perforated titanium foils showed remarkable performance in polymer electrolyte membrane water electrolysis by lowering the cell resistance. The combination of laser-perforated titanium foil and standard PTL resulted in lower high-frequency resistance (HFR) compared to the standard PTL.

We report on our progress in developing a compact laser that uses thulium-based fiber CPA technology emitting >30W at 2 µm and a >100W ultrafast laser for scientific applications based on coherent combination.

We present our progress on developing an innovative compact thulium-based fiber CPA emitting at 2 µm central wavelength. The laser parameters comprise >100 µJ pulse energy at an average power of >30W. The system comes in an industrial-grade platform optimized for long-term operation and its optimized packaging is well suited for the integration in laser machines for materials processing. The laser parameters are ideally suited for processing semiconductors, e.g. silicon by microwelding or cutting of filaments.

We present our recent progress in developing an innovative compact thulium-based fiber CPA emitting at 2 µm central wavelength based on an industrial-grade platform optimized for long-term operation.

Perforation of lithium-ion battery electrodes has recently become an increasing interest in science and industry. Perforated electrodes have shown improved electrochemical properties compared to conventional, nonperforated electrodes. It has been demonstrated that through perforation, the fast-charging capability and the lifetime of these batteries can be significantly improved. The electrodes for lithium-ion batteries consist of a copper foil onto which the electrode material is applied as a porous layer. This layer is mainly composed of active material particles, which are bound together by a binder phase. Here, synthetic graphite was used as an active material. Up to now, it has been shown that an advantageous and precise perforation geometry can be produced by ultrashort laser pulse ablation. Since the ablation volumes during perforation of the porous electrode material with ultrashort laser pulses are unusually high compared to solids, this work investigates the parameter dependency on the ablation mechanisms in detail. For this purpose, in particular, single-pulse ablation was investigated with respect to the ablation thresholds at different pulse durations. The pulse durations were varied over a large range from 400 fs to 20 ps. By varying the number of pulses per perforation up to 50 and the single-pulse energy up to 45 μJ, it could be shown that a homogeneous ablation down to the conductor foil through the 63 μm thick active material layer can be achieved.

The industrial maturity of ultrashort pulsed lasers has triggered the development of a plethora of material processing strategies. Recently, the combination of these remarkable temporal pulse properties with advanced structured light concepts has led to breakthroughs in the development of novel laser application methods, which will now gradually reach industrial environments. We review the efficient generation of customized focus distributions from the near infrared down to the deep ultraviolet, e.g., based on non-diffracting beams and 3D-beam splitters, and demonstrate their impact for micro- and nanomachining of a wide range of materials. In the beam shaping concepts presented, special attention was paid to suitability for both high energies and high powers.

We report on ultrashort pulsed laser fabrication strategies for glass articles with customized edges and curved surfaces. To achieve single-pass, full-thickness modifications along the entire substrate processing optics are presented that allows for beam shaping of non-diffracting beams and, additionally, for aberration compensation of phase distortions occurring at the tilted or curved interfaces. The efficacy of our concepts is presented by evaluating the surface and edge qualities of separated glass tubes with complex inner and outer contours as well as glass chamfer structures.

Ultrashort pulsed lasers represent unique tools for the processing of micro-optical components. Pulse durations around 1 ps and corresponding extreme peak intensities lead to interaction processes with all conceivable materials. As parts of almost every optoelectronic device, transparent materials represent a particularly challenging example for processing. Here, a controlled energy deposition at the surface or inside the volume is required while maintaining optical properties or implemented functionalities of adjacent areas. The talk will review strategies for the micro-processing of transparent materials that become possible by spatiotemporal beam shaping. Here, the beneficial use of non-diffracting beams is discussed as well as 3D-beam splitting approaches.

We generalize the well-known method of generating nondiffracting beams based on axicons in the near-field using phase modulations with azimuthal dependencies. The enormous benefit of our concept for efficient shaping of nondiffracting beams with arbitrary transverse profiles is shown and optimized processes like cleaving of particularly thin and thick glasses using elliptical Bessel-like beams are discussed.

During the last years processing of transparent materials by ultrashort laser pulses has gained interest. Spatial and temporal pulse shaping has already proven its potential for advances, widening existing and opening new application fields. The paper focuses on supporting the application development by extending pump-probe diagnostics via combining pulse shaping capabilities, dynamical beam positioning, processing at elevated repetition rates, energy modulation and high temporal resolution over an essentially infinite range of delay. Applying these capabilities gives inside into effects resulting from spatial and temporal shaping, on the laser matter interaction of individual and of a multitude of pulses, the latter typically effective on larger scales due to accumulation. The influence of beam shaping and processing parameters on the dynamic development of the interaction zone in multi pulse exposure highlights the potential of such diagnostic tools. Observations relevant for development of transparent materials processing ultrafast lasers by absorption induced inside of the workpiece are presented. Initiation and development of cracks as a major aspect in brittle materials processing can be analyzed in detail. Pump-probe polarization microscopy for transient stress birefringence observation reveals that both, pressure waves and temperature gradients from accumulation, are of major importance in scaling industrial processing. Considering these findings facilitates addressing different application fields, illustrated by examples on ultrafast welding and selective etching by shaped beams.

The modification of transparent materials is enabled by focused ultrashort laser pulses. Single pass processing up to several millimeters can be achieved by the usage of elongated beam profiles. We studied the mechanical separability in dependence of the material thickness. As simulations show, asymmetric beam profiles can cause modifications with preferential direction reducing the necessary breaking force. Pump-probe microscopy is implemented to examine the laser-matter-interaction. We present a measured 3D-reconstruction of the transient interaction inside the material and elucidate the desired crack formation. We demonstrate beam shaping concepts to create a new, efficient and robust class of Bessel-like beams, which can be used to achieve a preferred crack direction. We verify the concept by modification and separation of silicate glasses.

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.

Laser-induced cell injury in closed micro physiological systems: a novel method to study regeneration processes in vitro

We generalize the well-known method of generating nondiffracting beams based on axicons in the near-field using phase modulations with azimuthal dependencies. The enormous benefit of our concept for efficient shaping of nondiffracting beams with arbitrary transverse profiles is shown and optimized processes like cleaving of particularly thin and thick glasses using elliptical Bessel-like beams are discussed.

The remarkable temporal properties of ultra-short pulsed lasers in combination with novel beam shaping concepts enable the development of completely new material processing strategies. We demonstrate the benefit of employing focus distributions being tailored in all three spatial dimensions. As example advanced Bessel-like beam profiles, 3D-beam splitting concepts and flat-top focus distributions are used to achieve high-quality and efficient results for cutting, welding and drilling applications. Spatial and temporal in situ diagnostics is employed to analyze light-matter interaction and, in combination with flexible digital-holographic beam shaping techniques, to find the optimal beam shape for the respective laser application.

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.

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.

Pico- and femtosecond lasers with kilowatt average power levels that are also capable of providing multi-mJ pulse energies will be described. Well established 24/7 industrial ultrafast laser processes allow for an outlook on potential future applications. © 2019 The Author(s)