Phase-matched frequency conversion in ionizing atomic gases.

Abstract

We solve the one-dimensional wave equation for high-order mixing of the type ${\ensuremath{\omega}}_{h}=q{\ensuremath{\omega}}_{0}\ensuremath{-}l{\ensuremath{\omega}}_{c}(q\ensuremath{\gg}l>=1)$ using a Keldysh-type model to describe the high-field atomic nonlinear susceptibility. When ${\ensuremath{\omega}}_{c}$ is selected to give static phase matching, we show that the conversion efficiency of the mixed field can be increased by about an order of magnitude compared to non-phase-matched high-order harmonic generation but that fundamental limitations are introduced by axial electron-density gradients.