Studies of collisional and nonlinear radiative processes for development of coherent UV and XUV sources

High spectral brightness rare gas halogen (RGH) sources can be used to generate coherent extreme ultraviolet radiation by either harmonic generation mechanisms or direct multiquantum excitation of appropriate gain media. In order to demonstrate the basic characteristics of these two approaches, recent comparative measurements have been made. With the use of a 4 GW 193 nm (ArF*) system operating at a pulse duration of 10 ps, harmonic generation has been studied in several atomic and molecular media and used to generate 20 kW at 64.3 nm and 200 W at 38.6 nm. In addition, stimulated emission in molecular hydrogen on both the Lyman and Werner bands excited by two quantum absorption at 193 nm, has resulted in the generation of radiation as short as 117.6 nm at an efficiency of conversion approaching one percent. It has been concluded that the latter method is superior for the generation of short wavelength radiation. Extension of these results to both shorter wavelengths and higher power levels requires the ultraviolet. Recent studies of collision-free multiply-charged ion production with irradiation at 193 nm point to an anomalously strong coupling to high Z materials with processes involving as many as 99 quanta being observed. These multiquantum processes in the 40 - 80 eV range in certain atomic systems can be generated with existing laser instrumentation.