Nonlinear optical mode coupling by ionization in an Ar-filled capillary with high-power short-pulse excitation

High-power ultrashort laser pulses at near-infrared wavelengths propagating in gas-filled capillaries can form a compact source of XUV/soft X-ray radiation by high-harmonic generation (HHG) [1]. Maximization of the frequency conversion efficiency requires a detailed understanding of the atomic interaction mechanism as well as the propagation properties of both the near-infrared pump in the presence of a partially ionized gas and of the generated XUV. Here we focus on the numerical simulation of pulse propagation in a parameter regime dominated by plasma effects and by the nonlinear properties of ionization, and compare the results with experimental observations.