Nonlinear Compression of a 2.08-μm Regenerative Amplifier with Bulk Multipass Cell

High-power and high pulse energy ultrafast 2-μm laser systems are promising for many applications, including as driving sources for numerous secondary sources for scientific applications. In this regard, Ho-based solid-state lasers operating at 2.1 μm are promising for power- and energy-scaling, however, they suffer from gain narrowing, restricting available pulse duration to the picosecond-range and calling for efficient nonlinear compression methods, to address scientific applications. Herriott-type multi-pass cell (MPC) compressors have been shown to be promising in this regard achieving high compression ratio, and high optical transmission in a wide variety of pulse energy ranges [1], with most demonstrations so far being restricted to the 1 μm spectral region, and a few first demonstrations at 2 μm based on gas-filled cells. In [2], 138-fs 217- μJ pulses were compressed to 35 fs, 170 μJ at 1.94 μm. Most recently, compression of a Tm-doped CPA at 1.93- μm, from 98 fs to 20 fs with 1.5-mJ pulses was also demonstrated [3]. Although this pulse energy level has been shown to be compressible with more simple bulk/air MPC configurations [4], so far, no attempts have been made to use bulk compression at this wavelength. In this work, we demonstrate nonlinear pulse compression using bulk-based MPC in ambient air for the first time in the 2- μm wavelength range. We compress a 100-kHz, 80- μJ, 750-fs pulses generated from a home-built Ho:CALGO CPA at a central wavelength of 2.08 μm down to 98-fs pulse duration, achieving 525-MW peak power, with a high optical transmission of 90 % and preserving a good beam quality.