Effect of laser focus in two-color synthesized waveform on generation of soft x-ray high harmonics

Abstract

The synthesis of multi-color laser pulses has been developed as a promising way to improve the low conversion efficiency of high-order harmonic generation (HHG). Here we systematically study the effect of laser focus in the two-color waveform on the generation of macroscopic HHG in the soft X-rays. We find that the dependence of HHG yields on laser focus at low or high gas pressure is sensitive to the characteristics of single-atom harmonic response, in which “short”- or “long”-trajectory emissions can be selectively controlled by changing the waveform of two-color synthesized laser pulse. We uncover the phase-matching mechanism of HHG in the gas medium by examining the propagation of two-color waveform and the evolution of time-frequency emissions of high-harmonic field. We further reveal that the nonlinear effects, such as geometric phase, atomic dispersion, and plasma defocusing, are responsible for the modification of two-color waveform upon propagation. This work can be used to find a better macroscopic conditions for generating soft X-ray HHG by employing the two-color optimized waveform.

Control of quantum paths in harmonic generation through orthogonal fields specific frequency ratios

“…In additionThe photoelectron momentum distributions of the N 2 molecule depends on the orientation of the molecule, providing an aid in probing the interior of the molecule with ultrafast electron dynamics [17]. To generate supercontinuum high-order harmonics and synthesize isolated attosecond pulses, various schemes have been proposed, including few-cycle laser pulses [18][19][20], two-color fields [21][22][23], and polarization gating [24][25][26].…”