Development of Highly-Efficient Generation-Method for Vacuum-Ultraviolet Coherent Radiation

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The aim of this project is to develop a new type of highly-efficient generation-method for vacuum-ultraviolet coherent radiation based on nonlinear sum-frequency generation in gas-phase atoms. Gas-phase atomic hydrogen was chosen as a nonlinear medium. Coherent VUV-radiation at 122 and 103 nm (Lyman-alpha and beta radiation) was generated without suffering resonant absorption. The most important point of this method is to use an exact resonance condition for atoms for obtaining a resonantly enhanced huge nonlinearities for the medium, and simultaneously to remove resonant absorption for obtaining a transparency for the generated radiation using quantum interferences induced by strong-coupling.As a fundamental laser radiation source, a new type of single-longitudinal-mode pulsed-dye-laser was developed, which generates temporally smooth Fourier limit laser-pulse with smooth spatial profile. The smoothness both in temoral and spatial aspects is an essential issue to achieve experimental conditions for realizing the theoretical predictions. The nonlinear medium ; atomic hydrogen system, was prepared with a maximum atom-density of 5x10^<14> cm^<-3> at a temperature of 300 K through a microwave discharge for H_2 gas of 0.1 to 1 Torr.Basic physical characteristics for nonlinear optical processes using quantum interferences were investigated theoretically and experimentally. The sum-frequency generation experiments were carried out under strong-coupling condition using 40 MW/cm^2 excitation intensity with an interaction length of 5 cm. A conversion efficiency of 2x10^<-4> was achieved for 122 and 103 nm radiation. The obtained efficiency is a very high value considering the atom-density and excitation intensity. The present generation method using atmic hydrogen may offer a new possibility for various applications, such as to monitor atomic hydrogen.