Phase-matched generation of short wavelength, ultrashort-pulse light in capillary waveguides

Abstract

We demonstrate that a balance of gas and waveguide dispersion can be used to phase-match the upconversion of ultrafast pulses into the deep-ultraviolet and the extreme-ultraviolet regions of the spectrum. Ultrashort pulses tunable in the range 200-305 nm are obtained with a peak efficiency >18% by mixing the Ti:sapphire second harmonic with either the fundamental or the output of an optical parametric amplifier in a gas-filled capillary waveguide. Since neutral gases are anomalously dispersive to XUV high-order harmonics, these may be directly phase-matched without the need to use difference-frequency mixing. For high-harmonic generation, we have obtained an increase of conversion efficiency of 100-1000x over that obtained using a gas jet.