The interaction of ultrashort laser pulses with materials enables precise surface processing and has been in the focus of research due to its scientific and technological significance. While the fundamental processes of energy deposition, internal energy transfer, and material response are not yet fully understood, advances in experimental techniques have provided valuable insights into these phenomena. Here, we introduce an advanced optical broadband pump-probe setup for transient reflectivity measurements with sub-10 fs time resolution. The excitation takes place at 780 nm with a pulse length of 80 fs and variable fluence. We use broadband, few-cycle pulses for probing the material response which is crucial for gaining deeper insights into the early-time dynamics of light matter interaction and thus contribute to further understanding of the involved physical processes. We present measurements on bulk gold above the modification threshold benchmarking the performance of the setup. The behavior of gold under femtosecond irradiation is theoretically modelled and compared with the measurement results.

Ultrafast laser interference ablation leads to deterministic, strictly periodic patterns on metals and semiconductors with periods down to a few 100 nm. Manipulation of the interfering partial beams enable a variety of surface patterns with applications in photonics, fraud protection, electronics, fluidics, tribology, and medicine. Under suitable excitation conditions, a single beam may generate a surface plasmon polariton (SPP) and their interference may create a periodic surface pattern as well. Specific beam shaping may compensate the strong SPP attenuation leading to homogeneous patterns with a single laser pulse.

Interference of two or more overlapping coherent laser beams leads to a spatially periodic intensity modulation. Placing a material surface at this position and applying a sufficiently high intensity level will lead to a permanent surface modification, e.g., a periodic relief structure. The coherent beams are usually generated by splitting of one beam into several partial beams and recombining them on the material surface. In order to obtain specific intensity distributions, the partial beams can be manipulated concerning their amplitude, phase, and polarization. Various arrangements for beam splitting and recombination are presented. Amplitude or phase gratings, diffractive or refractive elements, or spatial light modulators are used. The obtainable minimal feature size depends on the wavelength and the interference angle of the beams. Structure details of the periodic patterns depend on the beam parameters, the material, and the environment. Grooves, ridges, bumps, spikes, droplets, and subsurface voids are observed. Such periodic patterns give rise to numerous applications in various fields like photonics, fraud protection, electronics, fluidics, tribology, and medicine. Examples are diffractive marking or changing the cell growth properties on medical implants.

Ultrafast high-energy laser systems allow performing some of the most advanced experiments in physical sciences, such as electron and ion acceleration, as well as high-harmonic and XUV generation. In the past decades, together with the development of optics, the field has tremendously developed towards high-energy/high-power ultrafast lasers. SAVANNA-HP is one of the latest developments towards this goal; a stretched flexible hollow-core fiber compressor designed for high-power lasers with ten mJ pulses and an average power of more than hundred Watts. The talk will cover the development and commissioning of such a device as well as its performance revealing state-of-the-art results.

The laser interference patterning of a silicon surface via UV femtosecond pulse irradiation, resulting in 350 nm periodic structures, is demonstrated. The structuring process was performed using a laser with a 450 fs pulse duration at a wavelength of 248 nm in combination with a mask projection setup. Depending on the laser fluence, single-pulse irradiation leads to amorphization, structure formation via lateral melt flow or the formation of voids via peculiar melt coalescence. Through multipulse irradiation, combined patterns of interference structures and laser-induced periodic surface structures (LIPSS) are observed.

Abstract Understanding the mechanisms and controlling the possibilities of surface nanostructuring is of crucial interest for both fundamental science and application perspectives. Here, we report a direct experimental observation of laser-induced periodic surface structures (LIPSS) formed near a predesigned gold step edge following single-pulse femtosecond laser irradiation. Simulation results based on a hybrid atomistic-continuum model fully support the experimental observations. We experimentally detect nanosized surface features with a periodicity of ∼300 nm and heights of a few tens of nanometers. We identify two key components of single-pulse LIPSS formation: excitation of surface plasmon polaritons and material reorganization. Our results lay a solid foundation toward simple and efficient usage of light for innovative material processing technologies.

Surface plasmon polaritons may induce a spatially modulated heat profile, which can cause the formation of laser-induced periodic surface structures (LIPSS). This contribution summarizes theoretical approaches and experimental verifications at different laser fluence regimes.

We present a CEO-stable 1.1 kW CPA system that is designed to drive a few-cycle-generation stage ( 300W of average power at 100kHz repetition-rate providing <10fs pulses. The chirped-pulse-amplification system (CPA) demonstrates excellent noise properties with <220mrad of the integrated carrier-envelope-offset (CEO) noise (10Hz to 20MHz) at a pulse repetition rate of 80MHz while the relative-intensity-noise (RIN) stayed <0.3%. This is the first CEO-stable laser system at 1kW level average power.

Few-cycle laser systems providing both high repetition rates and high pulse energies are a major focus of next-generation light sources. Consequently, the research facility of the Extreme Light Infrastructure (ELI) that is devoted to the generation of isolated attoseconds pulses, (ELI-ALPS in Szeged, Hungary), has set the demand for a laser system delivering carrier-envelope phase (CEP) stable pulses with 5 mJ of pulse energy, 6 fs pulse duration at 100 kHz repetition rate, which corresponds to an average power of 500 W [1] . This laser system, that is named HR2 (the high-repetition-rate beam line), is currently under development at Active Fiber System GmbH. Achieving these ambitious laser parameters is done by merging the robust techniques of coherent combination as an average-power scaling concept and the use of stretched hollow-core fiber technology for nonlinear pulse compression [2] .

We present the latest development of the ELI-ALPS HR2 laser towards a 5mJ, 6fs CEP stable output, which will be enabled by post-compression of >1kW, >10mJ fiber CPA system in an 8m long stretched hollow-core fiber.

A direct comparison of simulation and experimental results of UV laser-induced surface nanostructuring of gold is presented. Theoretical simulations and experiments are performed on an identical spatial scale. The experimental results have been obtained by using a laser wavelength of 248 nm and a pulse length of 1.6 ps. A mask projection setup is applied to generate a spatially periodic intensity profile on a gold surface with a sinusoidal shape and periods of 270 nm, 350 nm, and 500 nm. The formation of structures at the surface upon single pulse irradiation is analyzed by scanning and transmission electron microscopy (SEM and TEM). For the simulations, a hybrid atomistic-continuum model capable of capturing the essential mechanisms responsible for the nanostructuring process is used to model the interaction of the laser pulse with the gold target and the subsequent time evolution of the system. The formation of narrow ridges composed of two colliding side walls is found in the simulation as well as in the experiment and the structures generated as a result of the material processing are categorized depending on the range of applied fluencies and periodicities.

The fabrication of periodic surface patterns on various materials by ultrashort ultraviolet (UV) laser pulses is reviewed. Laser interference ablation using two or more coherent beams leads to deterministic, strictly periodic patterns. The generation of the interfering beams is accomplished by diffractive optical elements like gratings, grating systems or computer-generated holograms. The recombination of the diffracted beams is performed by optical imaging or diffractive beam management. Ultrashort UV pulses are especially suited for generating micron- to submicron-sized deterministic periodic patterns on metals and semiconductors.

Contemporary ultrafast science requires reliable sources of high-energy few-cycle light pulses. Currently two methods are capable of generating such pulses: post compression of short laser pulses and optical parametric chirped-pulse amplification (OPCPA). Here we give a comprehensive overview on the post-compression technology based on optical Kerr-effect or ionization, with particular emphasis on energy and power scaling. Relevant types of post compression techniques are discussed including free propagation in bulk materials, multiple-plate continuum generation, multi-pass cells, filaments, photonic-crystal fibers, hollow-core fibers and self-compression techniques. We provide a short theoretical overview of the physics as well as an in-depth description of existing experimental realizations of post compression, especially those that can provide few-cycle pulse duration with mJ-scale pulse energy. The achieved experimental performances of these methods are compared in terms of important figures of merit such as pulse energy, pulse duration, peak power and average power. We give some perspectives at the end to emphasize the expected future trends of this technology.

Here we present the latest experimental results of a high-power CEP-stable FCPA system. The 16-channel FCPA runs at 0.3% RMS power stability (>9hours) delivering more than 1kW and 10mJ after the compressor at a pulse duration of 280fs. To generate 6fs pulses, stretched hollow-core fibers are being employed. We present a significant up-scaling of this technique towards an output of 5mJ, 100kHz and 6fs.

Metal implants used in trauma surgeries are sometimes difficult to remove after the completion of the healing process due to the strong integration with the bone tissue. Periodic surface micro- and nanostructures can directly influence cell adhesion and differentiation on metallic implant materials. However, the fabrication of such structures with classical lithographic methods is too slow and cost-intensive to be of practical relevance. Therefore, we used laser beam interference ablation structuring to systematically generate periodic nanostructures on titanium and steel plates. The newly developed laser process uses a special grating interferometer in combination with an industrial laser scanner and ultrashort pulse laser source, allowing for fast, precise, and cost-effective modification of metal surfaces in a single step process. A total of 30 different periodic topologies reaching from linear over crossed to complex crossed nanostructures with varying depths were generated on steel and titanium plates and tested in bone cell culture. Reduced cell adhesion was found for four different structure types, while cell morphology was influenced by two different structures. Furthermore, we observed impaired osteogenic differentiation for three structures, indicating reduced bone formation around the implant. This efficient way of surface structuring in combination with new insights about its influence on bone cells could lead to newly designed implant surfaces for trauma surgeries with reduced adhesion, resulting in faster removal times, reduced operation times, and reduced complication rates.

The development of ultra-intense and ultra-short light sources is currently a subject of intense research driven by the discovery of novel phenomena in the realm of relativistic optics, such as the production of ultrafast energetic particle and radiation beams for applications. It has been a long-standing challenge to unite two hitherto distinct classes of light sources: those achieving relativistic intensity and those with pulse durations approaching a single light cycle. While the former class traditionally involves large-scale amplification chains, the latter class places high demand on the spatiotemporal control of the electromagnetic laser field. Here, we present a light source producing waveform-controlled 1.5-cycle pulses with a 719 nm central wavelength that can be focused to relativistic intensity at a 1 kHz repetition rate based on nonlinear post-compression in a long hollow-core fiber. The unique capabilities of this source allow us to observe the first experimental indications of light waveform effects in laser wakefield acceleration of relativistic energy electrons.

Summary form only given. The ELI-ALPS facility requests lasers with parameters beyond current state-of-the-art [1]. One of the most challenging ones is the high repetition rate laser 2 (HR2), a carrier-envelope-phase stable laser system delivering 5mJ pulses at 100kHz repetition rate and with pulse durations of 6fs, which is currently under development at Active Fiber Systems GmbH. It uses a kW-class ytterbium doped femtosecond fiber-chirped-pulse amplifier system. To achieve the bandwidth required for few-cycle pulses significant nonlinear spectral broadening is necessary. The latter technology has seen rapid scaling both in terms of average power [2] and pulse energy [3,4]. Furthermore, by the introduction of stretched hollow capillaries [5] high-quality long waveguides became available, which is inevitable for upscaling the pulse energy. Despite first promising experiments with ytterbium-based laser systems the average power used in combination with stretched-hollow-core fibers has not exceeded a few Watt yet [6,7]. In this contribution, we present a significant up-scaling of the average power of stretched hollow-core-fibers by spectrally broaden 5mJ, 500W, 280fs pulses in a 4m long, 450μm inner diameter fiber to a bandwidth supporting sub-17fs pulses. The laser system used for this experiment is a fiber CPA that incorporates coherent combination of multiple main amplifier channels achieving 5mJ pulse energy at 100kHz repetition rate corresponding to 500W of average power and 290fs pulses [8]. The output beam was sent through a combination of a half-wave plate and a thin-film polarizer to provide arbitrary attenuation of the power and then coupled to the 4m long capillary with an inner diameter of 450μm. The capillary had a pressure gradient with vacuum at the entrance and 600mbar Ar at the output side. The fiber transmission was nearly constant over the full power range up to 500W. At the maximum power the spectrum was significantly broadened to a bandwidth supporting sub-17fs pulse duration at 3mJ energy and 300W average power (Fig.1). In conclusion, we have shown significant scaling potential of stretched capillaries by demonstrating the highest combination of average power and pulse energy in any spectral broadening experiment presented to date. Further power scaling and pulse compression experiments are underway to achieve 500W, 5mJ, 6fs at 100kHz.

We present a laser source delivering waveform-controlled 1.5-cycle pulses that can be focused to relativistic intensity at 1 kHz repetition rate. These pulses are generated by nonlinear compression of high-temporal-contrast sub-25\,fs pulses from a kHz Ti:Sapphire double-chirped pulse amplifier in a stretched flexible hollow fiber compressor scaled for high peak power. The unique capabilities of this source are demonstrated by observing carrier-envelope phase effects in laser-wakefield acceleration of relativistic electrons for the first time.

In this contribution we report on the possibilities of dry and lubricated friction modification introduced by different laser surface texturing methods. We compare the potential of Laser-Induced Periodic Surface Structures and Laser Beam Interference Ablation on 100Cr6 steel in a linear reciprocating ball-on-disc configuration using 100Cr6 steel and tungsten carbide balls with load forces between 50 mN and 1000 mN. For dry friction, we find a possibility to reduce the coefficient of friction and we observe a pronounced direction dependency for surfaces fabricated by Laser Beam Interference Ablation. Furthermore, Laser-Induced Periodic Surface Structures result in a load-dependent friction reduction for lubricated linear reciprocating movements. This work helps to identify the modification behaviour of laser generated micro structures with feature sizes of approximately 1 µm and reveals new possibilities for surface engineering.

We present sub-10-fs, 3.2mJ pulses at 100kHz repetition-rate. This significant upscaling of average power was achieved by using a 6-m-long stretched flexible capillary. Such a technique has the potential to revolutionize few-cycle laser beamlines.