Control of soft X-ray high harmonic spectrum by using two-color laser pulses

Abstract

We demonstrate the suppression of soft X-ray high harmonics generated by two-color laser pulses interacting with Ne gas in a gas cell. We show that harmonic suppression can occur at the proper combination of the propagation distance and gas pressure. The physical mechanism behind is the phase mismatch between "short"-trajectory harmonics generated at the early and later times through the interplay of geometric phase, dispersion, and plasma effects. In addition, we demonstrate that the position and depth of harmonic suppression can be tuned by increasing the gas pressure. Furthermore, the suppression can be extended to other laser focusing configurations by properly scaling macroscopic parameters. Our investigation reveals a simple and novel experimental scheme purely relying on the phase mismatch for selectively controlling soft X-ray tabletop light sources without adopting the filters for applications.

Spectral splitting and phase matching of the macroscopic high-order harmonic generation in intense laser fields

“…As we know, there are potential models and ionization rates much more accurate than a hydrogen-like model in Ar or Ne atoms, such as quantitative rescattering theory [18,29,30]. However, the hydrogenlike model has been employed extensively for the dipole matrix element of the source term in propagation, such as [15,28].…”

“…Recently, He et al [17] experimentally measured the spectral redshift in HHG from H 2 and D 2 , and they illustrated that the physical process of red shift is due to the laser-driven nuclear motion. Jin et al [18] demonstrated that the soft x-ray harmonics by two-color laser pulse can be suppressed with proper macroscopic parameters and illustrated the corresponding physical mechanism. Xue et al [19] presented that the spectrum modulation can be controlled by changing the relative delay between the extreme-ultraviolet (XUV) and the infrared (IR) pulse, and the spectrum modulation is sensitive to the XUV chirp.…”

Optical Waveform Synthesis and Its Applications

“…Moreover, the optimized waveforms proved to be robust at macroscopic scales with pressures of up to 1 bar. [ 166 ] Adding a third color to the ω–3ω field did not lead to a further significant enhancement of the HHG yield but definitely to a denser or more continuous spectrum, thus facilitating the generation of an IAP. Interestingly, when a ω–2ω configuration was chosen instead, only about one order of magnitude HHG enhancement was found.…”

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

“…[44][45][46][47][48][49][50][51] To take into account macroscopic conditions for HHG with optimized multi-color waveforms, for simplicity, it has been usually assumed that all colors are focused at the same plane. [42,43,[52][53][54] To the best of our knowledge, there are no studies to discuss how the macroscopic generation of HHG is affected if laser focuses are varied in the synthesis of multi-color waveforms.…”