2.05 µm CPA delivering 75 mJ pulses with 2.2 ps duration at a 1 kHz repetition rate

Abstract

We report on a high-energy Ho:YLF chirped pulse amplifier (CPA) operating at 1 kHz. The amplifier chain is composed of a regenerative amplifier (RA) and a power amplifier containing two stages. The 25-kHz seed source is an optical parametric chirped pulse amplifier based on a Yb:KGW laser. It delivers 44 µJ pulses centered at 2050 nm with a duration of 114 fs, of which 4 µJ can be utilized for seeding the Ho:YLF RA. Profiting from the high seed energy, gain narrowing is reduced and bifurcation instabilities are attenuated in the high-gain RA. The Ho:YLF RA generated pulses with 22 mJ energy in the saturated single-pulse regime. The pulse energy is scaled-up in two consecutive single-pass power amplifiers to 75 mJ corresponding to an average power of 75 W. The subsequent compression of the pulses results in 2.2 ps duration, corresponding to a peak power of 31 GW. The water cooled Ho:YLF amplifier chain is characterized by an excellent stability of 0.19% rms and a remarkable extraction efficiency of 22%. The demonstrated pulse energy and peak power are record values for few-ps CPAs operating near 2 µm wavelength.