High-order harmonic generation during different overlaps of two-colored pulses in laser-produced plasmas and gases

In high-order harmonic generation in low-dense media, the application of two-colored pump has been shown to enhance odd-order harmonics, as well as the generation of strong even harmonics. Here, we apply this approach to compare high-order harmonic generation from laser-produced plasmas and gases using different mechanisms of harmonic emission enhancement. We generate two-color pump (TCP, 806 nm + 403 nm and 1030 nm + 515 nm) using two nonlinear crystals of different thickness (0.2 and 0.4 mm in the case of experiments with plasmas using 806 nm pump; and 0.1 mm and 0.4 mm in the case of experiments with gases and plasmas using 1030 nm pump) to demonstrate the enhancement of odd and even harmonics in laser-produced plasmas and by applying weak second field (403 or 515 nm) at different overlaps of pump pulses. The high-order harmonic generation in two media using TCP pulses is optimized. We demonstrate the wavelength dependence and the prevailing role of the partial overlap between the two orthogonally polarized waves in laser-produced plasmas and gases over large ratios of the second-order and fundamental photons. Our results are supported by the non-perturbative single atom theory and the interference model simulations