Generation and Amplification of Subpicosecond Pulses in the VUV — Towards Soft X-Rays with Nonlinear Optics

Abstract

Due to the development of short-pulse powerful laser systems, interesting perspectives for the generation of coherent radiation at short wavelengths by nonlinear optical processes exist. So, high order harmonic generation up to the 109th or 135th order with wavelengths of 7.4 nm (168 eV) and 7.8 nm (159 eV), respectively, has been demonstrated, starting from a Ti:sapphire laser at about 806 nm /1/ or a high intensity Nd:glass laser system at 1.05 μm /2/. Harmonic generation has also been demonstrated using a subpicosecond KrF excimer laser at 248 nm, with the observation of shortest wavelengths at 10 nm (25th order) /3/. In these and further experiments /4,5/ it has been observed, that after an initial strong decrease of the intensity with the harmonic order, finally a plateau is reached with only a relatively slow decrease of the intensity up to a cut-off frequency. It seems to be interesting to extend the KrF laser conversion experiments and consider harmonic generation by even shorter wavelength lasers, with the possibility to generate soft x-rays by high efficient low order processes. Lasers that may be used for this concept are the discharged pumped excimers like ArF (193 nm), and F2 (157 nm) or even the electron beam pumped excimers like Xe2 (172 nm), Kr2 (146 nm), and Ar2 (126 nm).