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A Joule-class room-temperature diode-pumped solid-state laser was developed. The energy scaling of the 100 mJ 1064 nm seed pulse was realized by a series of two diode-pumped amplifiers. The gain medium consists in free combinations of Nd:YAG ceramics bonded to sapphire transparent heat sinks, to relax the thermal load induced by the 34 kW pump power. At low repetition rate, parasitic lasing was the main limitation to energy scaling. By choosing a gain module combination producing a step-like gradual doping concentration profile, mitigation of parasitic oscillations was observed, and the system delivered 2.8 J, 800 ps pulses at 2 Hz.

In this work, the performance of Ca 5 (BO 3 ) 3 F (CBF) single crystals was investigated for the third harmonic generation at 355 nm. A high energy conversion efficiency of 16.9% at 355 nm was reached using a two-conversion-stage setup. First, using a high peak power, passively Q-switched Nd 3+ :YAG/Cr 4+ :YAG microlaser based gain aperture in micro-MOPA, the second harmonic at 532 nm was achieved with lithium triborate (LBO) crystal, reaching 1.35 MW peak power. On a second step, laser pulses at 355 nm were generated using a 5 mm-long CBF crystal growth by TSSG method with energy, pulse duration and peak power of 479 µJ, 568 ps and 0.843 MW, respectively. These results are currently the highest reported for CBF material.

An Nd:YAG Micro-MOPA, based on a microchip master oscillator and power amplifier system with gain aperture beam cleaning, could generate sub-ns 200 mJ pulses with extremely high brightness of 18 PW/sr·cm 2 [Opt. Express268609 (2018)]. However, the system repetition rate was limited to 10 Hz, due to thermal problems occurring in the main amplifier rod under high-power operation. In this work, we achieved 100 Hz operation with pulse brightness of 11 PW/sr·cm 2 by optical compensation of thermal lensing, which was evaluated through calculations and an experiment.

High brightness compact microchip-seeded MOPA system was realized. Implementing a microchip preamplifier stage acting as gain aperture element lead to excellent output beam quality with M 2 = 1.4. At maximum amplification level, 235 mJ (0.4 GW) of output energy (power) was measured. Analysis of the effect of the preamplifier showed that this element increases the available beam intensity by two orders of magnitude without significant increase in system footprint. Final beam brightness was 18 PW/sr.cm 2 .