Phase matching, quasi phase matching and pulse compression in a single waveguide for enhancing high harmonic generation

We demonstrate enhancement of high harmonic generation in the technologically significant 95 eV photon energy region by combining phase matching, quasi phase matching, and pulse compression in a single gas-filled waveguide. The waveguide geometry allows us to use argon gas as the generating medium, which also leads to enhanced emission due to its higher nonlinearity. The induced shock front due to laser pulse compression in the ionizing gas medium also generates an X-ray continuum at low pressure, with a spectrum corresponding to an isolated, 50 attosecond, X-ray pulse.