Quasi-Phase Matching of High Harmonic Generation by Utilizing a Modulating Transverse Laser Beam(2/2)

High-harmonic generation (HHG) from laser-irradiated rare gases has been proven to be a reliable source of ultrashort coherent extreme-ultraviolet (EUV) or soft x-ray. HHG is a powerful tool for science due to the highly spatial and temporal coherence. However, the low conversion efficiency limits the applications. To enhance the conversion efficiency, the phase matching condition between the propagations of the driving pulse and the HHG in the medium. Adjusting the laser intensity and the gas density achieves the dispersion balance at low ionization ratio condition for phase matching. Higher laser intensity or highly ionized ion as the medium can enhance the cut-off frequency, but the unbalanced dispersion results in the phase mismatches. In this project, we propose to utilize a transverse modulated laser beam to achieve the quasi-phase-matching (QPM) of HHG for the enhancement of the conversion efficiency and the cut-off frequency based on the superiority of high intensity at Nation Central University laser facility. This scheme shows merits: (1) HHG yield exponentially grows with the length medium; (2) high intensity laser and highly ionized ion extend the HHG to soft X-ray; (3) the HHG is tunable and selective based on this scheme; (4) the setup is concise. For running this project, we have developed HHG tomography helping us to observe the dynamics of HHG yields during the interaction. This HHG tomography also help us reshape the transverse laser beam precisely for QPM-HHG. We also developed a simulation for the the calculations of the driving pulse propagation and the ionization ratio distribution during the interaction, and the investigations of QPM-HHG by a transverse modulated laser beam. HHG will have the scientific and technologic potential for applications once conversion efficiency and the cut-off frequency can be enhanced, and it will cause the positive impact on society, economy, and international status for Taiwan.