Efficient extreme-ultraviolet multi-band high-order wave mixing in silica

Solid-state high harmonic generation (SSHHG) is a relatively recent,(1-4) non-destructive technique that offers new insight into the dynamics of strong-field light-matter interaction.(1-3,5-8) At the same time, SSHHG holds promise for being a viable route to engineering innovative, flexible, compact sources with emission in the extreme-ultraviolet (XUV) spectral range.(9,10) The technique has already been shown to yield XUV light,(3,11-13) albeit with low conversion efficiencies, as compared to the more traditional gas-based high harmonic generation (HHG) sources.(3,11) In this work we demonstrate that a non-collinear, multicolor SSHHG arrangement leads to spectra in the XUV with a high degree of tunability, and a considerable enhancement of the output flux. The observed behaviour can be understood in terms of perturbative optical wave mixing over more than one order of magnitude of the drive intensity. In addition, a model based on the recently-introduced injection current(8) allows accurate predictions over the entire experimental range.