Experiments and Numerical Simulations of Ho:CALGO Regenerative Amplifier at 2.08 μm

High-power ultrafast laser sources in the short-wave infrared region are in high demand for driving nonlinear wavelength conversion and material processing, among others. Among existing technologies to access this wavelength, Ho-based laser amplifier systems are promising for power and energy scaling due to their operation wavelength of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$2.1\mu \mathrm{m}$</tex>, exhibiting high atmospheric transparency. The large energy storage capability of Ho-doped materials due to their large gain cross sections and long upper-level lifetime is suitable for high-gain amplifiers such as a regenerative amplifier (RA). Moreover, commercially available high-power <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$1.9-\mu \mathrm{m}$</tex> Tm fiber lasers facilitate the realization of high-power, high-energy Ho-based laser amplifier systems. So far, numerical studies and experimental realization have been demonstrated mostly based on Ho:YLF crystals [1], and tens of mJ level amplifications were achieved [2], however, the pulse duration was limited to few picosecond regime due to narrow and structured gain profile of Ho:YLF. Ho-doped disordered CaAlGdO<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</inf> (CALGO) crystal is an attractive alternative for high-power femtosecond amplifiers due to the combination of broad gain bandwidth and relatively high gain cross section, however so far was only explored for short pulse oscillators and not for high energy amplification. Here we present our latest results using Ho:CALGO for regenerative amplification. We demonstrate a 750-fs, <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$112-\mu \mathrm{J}$</tex>, 100-kHz Ho:CALGO RA based on a chirped pulse amplifier (CPA) arrangement with CW Tm fiber laser pumping, reaching a peak power of more than 100 MW. Furthermore, we present numerical simulations for further energy amplification towards multi-mJ operation at different repetition rates.