Above-mJ optical parametric chirped pulse amplifier at 3 μm for laser-driven coherent soft x-ray generation beyond the water window

Optical parametric chirped pulse amplification (OPCPA) provides an excellent platform to generate ultrashort mid-infrared pulses in the spectral window beyond the scope of traditional mode-locked lasers. This technology has paved the path toward tabletop coherent soft x-ray (SXR) sources in recent years. Commercial availability of high-power Yb:YAG lasers as the pump lasers has enabled OPCPA to generate high-energy femtosecond mid-IR pulses at a high repetition rate. However, it is still difficult to achieve above mJ, high repetition rate OPCPA at 3 μm with less than 100 fs pulsewidth. Here, we present a 10 kHz, few-cycle OPCPA at 3.1 μm generating compressed pulses of 1.1 mJ energy with a record temporal width of 58 fs and an excellent rms stability of 0.8%. Our experimental results are further compared with two different simulation codes for optimization. To increase the amplification efficiency, we utilize a pulse-front tilt matching configuration resulting in 80% more energy in the first power OPCPA stage and expect up to 3 mJ of pulse energy in total with all three power OPCPA stages. These pulses open up the opportunity to access, in particular, the magnetically dichroic L-absorption edges of the 3d metals through the generation of ultrashort SXRs via high harmonic generation beyond the water window (500–900 eV) in a laboratory setup. This provides the prospect of availing femtosecond pump-probe spectroscopy with SXR pulses for studying the electronic structure dynamics of numerous condensed phase systems via resonant transitions from core levels of functionally relevant metals without having to resort to large-scale facilities.