Development of vacuum ultraviolet Ar_2 excimer laser by laser-heated plasma pumping

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In order to realize a practical Ar_2 excimer laser, we have proposed a new pump scheme to deposit a high power density into a high pressure Ar gas without discharge instability[7-9], In this scheme, a pre-ionized high-pressure Ar gas is irradiated by an intense CO_2 laser beam. The initial electrons are accelerated and heated by the electric field of the CO_2 laser, and an Ar gas is effectively ionized. The advantage of this scheme is that a rapid and intense energy deposition into the gas plasma is possible without being limited by discharge instability. In this paper, we report the vacuum ultraviolet emission characteristics from such a laser-heated high pressure Ar plasma.As the results, a 100 mm-long linear plasma was successfully produced in an Ar gas at a pressure of 20 atmospheres by heating the pre-ionized Ar gas with a TEA CO_2 laser. The VUV emission at 126 nm from the Ar_2 excimers was observed. Although no clear evidence of the stimulated emission has been observed yet, the results indicate that the plasma was produced by a proposed mechanism, not by a simple laser-breakdown. In the present experimental setup, the main components such as pre-ionizer and a set of focusing mirror are installed in a high-pressure gas chamber. This causes some problems in terms of the purity of gas, the pre-ionization and an optical alignment. We are further optimizing the system for the realization of the stimulated emission at 126 nm.