ABSTRACT
We report here experimental results of perturbative nonlinear optical wave-mixing processes in the extreme ultraviolet region by using two-color and three-color laser fields. Besides the usual odd-harmonic spectrum of high harmonic generation, new spectral components are observed when multiple incommensurate lasers (one driving plus one or two control field) interact with neutral krypton gas. To demonstrate the wave-mixing process underlying such an observation, we first couple the driving field with either the signal or the idler field of an optical parametric amplifier in the gaseous ensemble to generate certain mixing frequencies. The two control fields are then simultaneously combined with the driving field to produce broad and distinguishable mixing peaks that clearly reveal the contribution of each control laser. Finally, the variation of the intensity of the mixing waves with the intensity of each control field, the gas density, and the relative focus position is examined for signatures of phase-matched generation of the mixing fields in this spectral region.
ABSTRACT
We present a detailed study of the wave-mixing process in the extreme ultraviolet (XUV) region (around 30 nm) by using two collinear multiple-cycle laser pulses with incommensurate frequencies (wavelengths 1400 and 800 nm). The experimental data provide evidence for the coherent accumulation of wave-mixing fields and a high third-order response of the medium in this spectral range. We show that the time evolution of the mixing fields can be used to study the coherence dynamics of the free-electron wave packet with a lifetime of 200-750 fs.
