Generation of tunable XUV radiation by high-order frequency mixing

Abstract

Currently, there exists considerable interest in the generation of coherent radiation in the xuv spectral range. Due to the development of compact short-pulse highpeak power laser systems, high-order harmonic generation has become a useful laboratory tool. Harmonics up to very high orders and wavelengths below 10 nm have been demonstrated.1 For applications, tunable coherent XUV radiation is of great importance. One way to achieve this is to tune the main pump laser directly. However, the disadvantage of this approach is, that the high power lasers systems are only slightly tunable (excimer, Nd:glass) or if broadly tunable (Ti:sapphire) are optimized for a specific wavelength. A more flexible approach is to mix very powerfull pump laser radiation (ωP) with a less powerfull but tunable light source (ωOPG), generating tunable photons at n · ωP ± k· ωOPG. To achieve high orders in ωP (high n) intensities of more than 100 GW have been used, while for ωOPG intensities of about 100 MW are sufficient to detect at least mixing signals with k = 1. Similar experiments using the non-tunable second harmonic of a Nd: glass pump laser have been reported in [2].