Kilohertz extreme-ultraviolet light source based on femtosecond high-order harmonic generation from noble gases
A compact, versatile table-top kilohertz source of coherent extreme-ultraviolet (XUV) radiation in the wavelength region 18-100 nm, based on high-order harmonic generation from noble gases induced by a 40-femtosecond Ti:sapphire laser system, is presented. The XUV beamline delivers at its output 108 photons/s at a wavelength of 23 nm. The monochromatized XUV radiation is directly focused onto a 10-2-mm2 spot by a toroidal grating, allowing one to reach intensities higher than 106 W/cm2. Optimization results are presented for a new XUV-generating geometry, utilizing a `semi-infinite' quasi-static gas cell and strong focusing. In those conditions, we observe an anomalous inversion between the cutoffs of argon and krypton, with the krypton spectrum extending to much higher orders than expected in an adiabatic limit.