Efficient above-mJ 62 fs OPCPA at 3.2 μm for soft x-ray generation up to 1 keV

We present an above-mJ optical parametric chirped pulse amplifier (OPCPA) at 3.2 μm with 62 fs pulse duration, operating at 10 kHz for coherent soft x-ray generation beyond the water-window in a laboratory setup. The high peak power is made possible by the implementation of pulse front tilt (PFT) technique, which has increased the conversion efficiency by 39% resulted in 2.7 mJ pulses at 10 kHz. The improved OPCPA performance is crucial for generating mid-IR pulses capable of driving coherent soft x-ray sources beyond the water window. High-harmonic generation (HHG) up to 1 keV in He is predicted based on the macroscopic simulations using the experimentally demonstrated pulse parameters. Table-top coherent soft X-ray sources capable of covering above 500 eV spectral range are of great interest since they allow to explore ultrafast dynamics of magnetic systems by probing the (magnetically dichroic) L-absorption edges of 3d metals in a laboratory setup.