Multi-colour cascaded wave-mixing for studying atomic and molecular dynamics

Abstract One of the specialized spectroscopic techniques used to analyze the interaction of a light field with a target atom or molecule is nonlinear four-wave mixing in the extreme ultraviolet (XUV) region. In this paper, we investigate the fundamental interaction of atomic argon and molecular nitrogen gases with a light field in the perturbative nonlinear regime by cascading high-order harmonic generation (HHG) radiation with a multi-color laser. We optimize the phase-matching of collinear, multiple-cycle laser pulses with incommensurate frequencies (800 nm, 1400 nm and 560 nm) in third-order nonlinear wave-mixing with HHG-XUV radiation. Using a single-gas-cell interaction chamber, we reveal the electron wave packet dynamics in atomic and molecular systems by examining the time-dependent spectral features of the wave-mixing field, including intensity and frequency modulation patterns. This simple experimental setup presents a novel spectroscopy technique that can provide deeper insights into target systems, and potentially more complex molecular gases, involving multi-electron interaction regimes.