An overview of the latest developments of kilowatt-level diode pumped solid state lasers for advanced applications at the HiLASE Centre is presented. An overview of subcontracted and in-house-developed laser beamlines is presented. The aim of development is to build kW-class beamlines delivering picosecond pulses between 1-and 100-kHz repetition rates and high-energy nanosecond pulses at 10 Hz. The picosecond beamlines are based on Yb:YAG thin-disk amplifiers and chirped pulse amplification. The current status of the beamlines' performance is reported. The advantages of zero-phonon line and pulsed OPEN ACCESS Appl. Sci. 2015, 5638 pumping are demonstrated with respect to efficiency, thin disk temperature and beam quality. New diagnostics methods supporting the high average power lasers' development, such as the high-resolution spectroscopy of Yb-doped materials, in situ thin disk deformation measurements, single-shot M 2 measurement, realization of wavefront correction by a deformable mirror and the laser performance of a new mixed garnet ceramics, are described. The energetic, thermal and fluid-mechanical numerical modeling for the optimization of the multi-slab amplifiers is also described.

A unique combination of the ultrashort high-energy pulsed laser system with exceptional beam quality and a novel Diffractive Optical Element (DOE) enables simultaneous production of 2601 spots organized in the square-shaped 1 × 1 mm matrix in less than 0.01 ms. By adjusting the laser and processing parameters each spot can contain Laser Induced Periodic Surface Structures (LIPSS, ripples), including high-spatial frequency LIPSS (HFSL) and low-spatial frequency LIPSS (LSFL). DOE placed before galvanometric scanner allows easy integration and stitching of the pattern over larger areas. In addition, the LIPSS formation was monitored for the first time using fast infrared radiometry for verification of real-time quality control possibilities. During the LIPSS fabrication, solidification plateaus were observed after each laser pulse, which enables process control by monitoring heat accumulation or plateau length using a new signal derivation approach. Analysis of solidification plateaus after each laser pulse enabled dynamic calibration of the measurement. Heat accumulation temperatures from 200 to 1000 °C were observed from measurement and compared to the theoretical model. The temperature measurements revealed interesting changes in the physics of the laser ablation process. Moreover, the highest throughput on the area of 40 × 40 mm reached 1910 cm2/min, which is the highest demonstrated throughput of LIPSS nanostructuring, to the best of our knowledge. Thus, showing great potential for the efficient production of LIPSS-based functional surfaces which can be used to improve surface mechanical, biological or optical properties.

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Laser treatment of amorphous TiO2 nanotube layers leads to their crystallization without deformation or formation of the thermal oxide layer.

Multi-beam micro- and nano-machining of material surfaces has been getting more important because of its great potential to increase production speed of large size laser induced periodic surface structures (LIPSS). Fast and cheap production of engineered surfaces structures can bring unique properties of surfaces like tailored wettability, friction, antibacterial properties, etc., to mass-production with consequence in, for example, energy and costs savings. However, tailoring of long-term stable interference patterns from ultrashort laser pulses requires an extremely stable laser system with nearly diffraction-limited output beams. HiLASE Centre developed such a thin-disk-based Yb:YAG sub-picosecond laser platform, PERLA, providing average output power up to 0.5 kW with 2nd and 4th harmonic generation extensions and demonstrated its potential for direct laser interference patterning (DLIP). In this paper, we focus on details of the thin-disk PERLA laser.

Abstract:The development of kW-class diode-pumped picosecond laser sources emitting at various wavelengths started at the HiLASE Center four years ago. A 500-W Perla C thin-disk laser with a diffraction limited beam and repetition rate of 50-100 kHz, a frequency conversion to mid-infrared (mid-IR), and second to fifth harmonic frequencies was demonstrated. We present an updated review on the progress in the development of compact picosecond and femtosecond high average power radiation sources covering the ultraviolet (UV) to mid-IR spectral range at the HiLASE Center. We also report on thin-disk manufacturing by atomic diffusion bonding, which is a crucial technology for future high-power laser development.

We report a high-brightness mid-IR diode-pumped laser based on 15 at.% Er:Y 2 O 3 ceramics operated at room temperature. Up to 0.95 W of output power at 2725 nm was obtained with a 17.4% slope efficiency with respect to the absorbed pump power and with an M 2 < 1.2. Furthermore, a maximum peak output power of 9 W was generated with pulsed pumping. Perspectives for further efficiency and power scaling are also considered.