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 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 M2 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.

https://www.mdpi.com/2076-3417/5/4/637/pdf

Status of the High Average Power Diode-Pumped Solid State Laser Development at HiLASE

In the project presented in this thesis, a laser system for the spectroscopy of muonic helium ions has been developed. Five 2S-2P transitions were successfully measured in 2013 and 2014 using this laser system. Eventually the alpha particle and the helion charge radii will be deduced from these measurements with accuracies of few parts per thousand. These values will be benchmarks for nuclear structure theories, and bear information contributing to the solution of the so-called proton radius puzzle. The laser system developed is composed of a thin-disk laser operated at a wavelength of 1030 nm pumped with a high-power diode laser. The pulses of the thin-disk laser are frequency-doubled and used to pump a Ti:sapphire laser. The pulsed Ti:sapphire laser is injection-seeded by a frequency-stabilized cw Ti:sapphire laser with a wavelength tunable between 800 nm and 970 nm. The pulses of the Ti:sapphire laser are then transported and coupled into the multi-pass cavity surrounding the volume the muons are stopped at. The most challenging building block of the laser system is the thin-disk laser. A thin-disk laser was developed based on a Q-switched oscillator followed by a multi-pass amplifier. The thin-disk laser has to deliver pulses with 100 mJ of energy, at average repetition rates of at least 200 Hz with stochastically distributed (in time) triggers having a minimal delay time between pulses down to 1.2 ms. In addition, pulse-to-pulse fluctuations smaller than a few % are required, as well as a latency time between trigger and emission of the pulse of < 500 ns, and good transverse beam mode quality of M < 1.1 for efficient frequency doubling. Special emphasis was devoted to the design of resonators and multi-pass amplifiers that minimizes the sensitivity to thermal lens effects. In addition, aperture effects that naturally occur in the pumped active medium have been discussed in detail in this thesis because they are usually neglected in the thin-disk laser community. Yet, they may play an important role in laser design. The laser development that has been motivated by the muonic helium spectroscopy has also led to several additional results published in papers reproduced in the second part of this thesis. As the first additional result, a novel multi-pass architecture is proposed that solves present energy scaling limitations of mode-locked multi-pass laser oscillators. Contrarily to the state-of-the-art layouts based on 4f-imaging, the stability region of our multi-pass resonator does not shrink with the number of passes at the active medium. Hence, our design sustains thermal lens variations that are by at least an order of magnitude larger compared to state-of-the-art multi-pass designs. This implies an order of magnitude larger output powers, and laser output pulses with mJ energy at MHz repetition rates directly from an oscillator. As second additional result, we expose a novel limitation for the power scaling of thin-disk lasers. This limitation is related to misalignment induced by thermal lens effects. From its modeling a parameter has been obtained that can be used to design laser resonators circumventing this limitation. IV The thin-disk laser for the 2S – 2P measurement in muonic helium The third additional result is related to novel pump optic schemes having an increased number of passes at the thin disk as compared to standard designs while maintaining the same requirement for the pump beam quality and size of the pump optics. V The thin-disk laser for the 2S – 2P measurement in muonic helium

The Thin-Disk Laser for the 2S – 2P Measurement in Muonic Helium

Novel thin-disk laser pump layouts are proposed yielding an increased number of passes for a given pump module size and pump source quality. These novel layouts result from a general scheme which bases on merging two simpler pump optics arrangements. Some peculiar examples can be realized by adapting standard commercially available pump optics simply by intro ducing an additional mirror-pair. More pump passes yield better efficiency, opening the way for usage of active materials with low absorption. In a standard multi-pass pump design, scaling of the number of beam passes brings ab out an increase of the overall size of the optical arrangement or an increase of the pump source quality requirements. Such increases are minimized in our scheme, making them eligible for industrial applications

Thin-disk laser pump schemes for large number of passes and moderate pump source quality

We demonstrate a carrier-envelope phase (CEP)-stable, KTA (KTiOAsO4)-based optical parametric amplifier (OPA) delivering 6-cycle (79 fs), 3.8-μm pulses at a 100-kHz repetition rate with an average power of 4.5 W. The pivotal achievement is the stable generation of supercontinuum (SC) seed pulses in YAG with 1.4-ps pulses, which are the longest for SC generation on its longer wavelength side to 2.2 μm. This technology offers a robust and simplified OPA architecture with characteristics of passively stabilized CEPs, simplified dispersion management with bulk materials, wavelength tunability for 1.3–4.5 μm for spectroscopy, and a proof of concept on its power scaling with kilowatt-class pump lasers. The total output power of 17 W (signal plus idler) is achieved, and this high photon flux opens novel statistics-driven spectroscopy for rare events in strong-field physics.

Supercontinuum-seeded, carrier-envelope,phase-stable, 45-W, 38-μm, 6-cycle, KTA optical parametric amplifier driven by a 14-ps Yb:YAG thin-disk amplifier for nonperturbative spectroscopy in solids

Research on the adjusting technology of the thin disk laser

A regenerative thin disk laser amplifier generating nanosecond pulses with an average power of 120 W at a repetition rate of 1 kHz with a nearly diffraction limited beam is presented.

Regenerative thin disk amplifier with a pulse energy of 120 mJ at 1 kHz

As a result of experimentally verified simulations of Yb:YAG regenerative amplifiers utilizing spectral broadening effects due to self-phase modulation, we provide a map for the optimized choice of initial chirp and internal group-delay dispersion (GDD) within the amplifier. We show that the shortest pulse durations can be obtained with negative internal GDD, being, however, limited by the damage threshold of the optical components due to increased peak powers and by a breakup of pulses comparable to the propagation of higher-order solitons. We propose that by usage of increasing amounts of positive internal GDD, along with a corresponding amount of negative initial GDD, the obtainable peak powers after compression can be scaled far beyond the usual gain-bandwidth limitation.

Generation of high-energy femtosecond pulses by use of spectral broadening effects in Yb:YAG thin-disk regenerative amplifiers

We present experimental and theoretical results for parallel amplification of 350 fs and 2.7 ps in the same Yb:YAG regenerative thin-disk amplifier for high energy OPCPA pumping and stable supercontinuum generation for OPCPA seeding.

Yb:YAG regenerative thin-disk amplifiers as an ideal pump and seed source for OPCPA

The invention relates to a laser amplifier system (1) with a solid state disk (2) comprising a laser medium and having two flat faces (3, 4), functional layers (5) comprising a reflector for a pump radiation field (6) and a reflector for a laser radiation field (7) being arranged on the first flat face (3), and the functional layers (5) being thermally and mechanically coupled to a cooling surface (8) of a cooling body (9) to dissipate heat, the coupling being brought about at least to some extent by an adhesive layer (10) that is arranged between the cooling body (9) and the functional layer (5). The laser amplifier system is characterized in that the adhesive layer (10) is formed by an adhesive that substantially changes its volume during transition from the liquid to the solid state. The invention further relates to a method for producing the laser amplifier system (1) according to the invention.

Laser amplifier system with solid state disk

Demonstration of a regenerative amplifier with “mixed pulse trains” for micromachining: femtosecond pulses for effective ablation directly followed by nanosecond pulses for smoothening of the surface amplified within one single thin disk resonator. © 2019 The Author(s)

Femtosecond + Nanosecond Multiple Pulse Train from a Thin Disk Regenerative Amplifier

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