Phase modulation in polarization beating quasi-phase-matching of high-order-harmonic generation

摘要

Polarization beating quasi-phase-matching (PB QPM) in high-harmonic generation (HHG) is currently understood as a purely-intensity-modulation quasi-phase-matching (QPM) technique. In PB QPM, the driver ellipticity oscillates during propagation, modulating the HHG conversion efficiency since the single-atom HHG yield decreases rapidly with increasing ellipticity of the driving laser. We show that PB QPM is in fact based on both intensity and phase modulations. Unfortunately, in PB QPM the intensity and phase contributions oppose each other, resulting in significant reduction in the QPM efficiency.