Comparison of 100-kHz Near-IR and Mid-IR Driven High-Harmonic Generation in the Water Window

To date significant efforts have been made to extend the cutoff energy of high-harmonic-generation (HHG) sources into the water window (283-543 eV). The HHG cutoff is extended with both longer wavelength and higher peak power [1] , with different efficiencies and phase matching trade-offs for these two approaches. Additionally, there are practical considerations since suitable lasers in the mid-IR are less widely available than in the near-IR. Here, we empirically studied at which crossover point one approach to high-photon-energy HHG outperforms the other. For this, we performed HHG in the same setup (described in [2] ) with two optical parametric chirped-pulse amplifiers (OPCPA) that share the same pump and seed lasers: a mid-infrared (mid-IR) [2] and a near-infrared system [3] , both operating at a repetition rate of 100 kHz. Results are presented in Fig. 1 .