Tunable high-order harmonic generation and the role of the folded quantum path

Abstract

We theoretically demonstrate the selective enhancement of high-order harmonic generation (HHG) in two-color laser fields consisting of a single-cycle fundamental wave ($800\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ wavelength) and a multicycle subharmonic wave ($2400\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ wavelength). By performing time-frequency analyses based on a single-active-electron model, we reveal that such an enhancement is a result of the modified electron trajectories in the two-color field. Furthermore, we show that selectively enhanced HHG gives rise to a bandwidth-controllable extreme ultraviolet supercontinuum in the plateau region, facilitating the generation of intense single isolated attosecond pulses.