Abstract

The technology of high spectral brightness rare gas halogen (RGH) excimer lasers can be readily used to generate bright coherent radiation in the extreme ultraviolet (XUV) range. As demonstrations of this capability, tunable (XUV) radiation at ~ 64 nm and ~ 79 nm has been generated using a high spectral brightness ArF^* (193 nm) source by frequency tripling and frequency mixing, respectively. In the case of tripling, it has been experimentally determined that the conversion efficiency is limited by photoabsorption of generated XUV photons by the nonlinear medium. It is shown that a simple flow geometry that confines the nonlinear medium to the conversion zone by a buffer gas of low absorption cross-section sharply reduces these losses and leads to correspondingly enhanced conversion efficiencies. With this apparatus, at 64 nm, 30 W, 10 nsec pulses have been generated corresponding to a conversion efficiency of 10^-6. This upconverted radiation is tunable over 0.2 nm, the range determined by the gain profile of ArF^* amplifiers. Broad tunability is achieved with the use of a dye laser in a process of frequency mixing. Tunable radiation with peak powers of 200 mW at ~ 79 nm has been generated by frequency mixing 2 ArF^* photons and one visible dye photon (420 - 460 nm). Since nonlinear processes generally favor the use of short pulses, 10 psec pulses at 193 nm have been generated by frequency tripling of a pulse amplified, synchronously pumped mode-locked dye laser. Amplified radiation of this source is used to obtain coherent radiation at 64 nm with a power of 20 kW by frequency tripling, a value corresponding to an enhanced conversion efficiency of ~ 10^-5. An analysis of the expected limiting performance of RGH systems for the production of XUV and soft x-rays will be given.

© 1982 Optical Society of America