GENERATION OF CW COHERENT RADIATION IN THE NEAR U.V.

Abstract
Following the demonstration of the second harmonic generation in 1961 by Franken, numerous non linear methods have been used associated with pulsed lasers to generate U.V. radiation in the range 200-300 nm. The corresponding sources are now widely used in the spectroscopic studies, but their limited monochromaticity makes them of poor interest in high resolution spectroscopy. There is for long time now a pronounced interest to have at one's disposal a radiation source which provides extremely narrow bandwith, convenient intensity and tunability, but it is only recently, with the advent of powerful CW dye lasers, and the development of enhancement technics that the first reliable sources have been demonstrated, and the first high resolution spectroscopy studies performed. We give in this paper a brief and then certainly incomplete review of the different progress that have been done in the generation of highly monochromatic U.V. radiation, as well as a review of the different experiments that have been performed in this frequency domain. We mainly deal with the use of non linear crystals in second harmonic generation and sum frequency mixing schemes, leaving for the conclusion the listing of the other possibilities of coherent CW U.V. generation that could be used in a near future.