V Generation of Tunable Coherent Vacuum-Ultraviolet Radiation

Abstract

This chapter reviews the general principles of frequency mixing and describes the experimental progress toward the attainment of tunable coherent radiation in the vacuum-ultraviolet (VUV) and XUV regions. The process of frequency mixing and third harmonic generation is best understood by means of the nonlinear susceptibility of atomic systems when irradiated by intense electromagnetic waves. Generation of VUV radiation by third harmonic and sum and difference-mixing has been demonstrated in the rare gases and in many metal vapors. This has been done with and without phase matching or resonance enhancement with corresponding conversion efficiencies of 10 –3 to 10 –5 . Much remains to be done in the XUV region before generally useful laboratory sources can be readily constructed, and the soft x-ray region has yet to be penetrated. Further developments undoubtedly improve the efficiencies, intensities, and range of tunability and monochromaticity of these light sources. However, it is important to stress that laser sources of high brightness are now available for application to a wide variety of scientific uses in the VUV and XUV regions.