Optimization of conversion efficiency and spatial quality of high-order harmonic generation

Optimization of high-order harmonic generation has been studied with a 30 fs laser at an intensity of < 2x10 14 W/cm2 in a quasi-static gas cell ([MATH]) filled with argon ([MATH]). The effect of propagation length and gas density on the conversion efficiency and spatial quality of high-order harmonics are investigated comprehensively. As a result of phase-matched propagation, both the spatial quality and conversion efficiency of the 29th harmonic are successfully optimized to Gaussian-like profile with a divergence of 4.5 mrad (full width at l/e2 maximum) and a saturated efficiency. A quasi-two-dimensional simulation confirms the phasematching effect