Pressure dependence of excimer emission induced by an intense uranium beam

In December 2005 a heavy ion beam pumped UV excimer laser has been successfully demonstrated for the first time in the experiments performed at the GSI-SISHHT target area [1,2]. The primary goal for this experiment was to demonstrate laser effect on the KrF line (λ = 248 nm) and to proof this using various methods. The dependence of spontaneous and stimulated emission from pressure and composition of the laser gas has also been studied. Unfortunately, absolute measurements were not yet possible in this pioneering experiment but the relative pressure dependencies of laser light and spontaneous emission could be studied. A mixture of an excimer gas mixture (99,5% Kr and 0,5% F2) and a buffer gas (pure Ar) was used as the laser medium. In order to avoid F2 depletion due to chemical reactions, a continuous flow of gas was maintained in the laser cell. The composition of the laser gas could be varied by changing the flow rates for the excimer and buffer gases. Basically, two mixing ratios of 65/35 and 40/60 for Ar/Excimer were used and the pressure was controlled within a region from 1.2 to 2 bar by adjusting the output valve. Examples of spectra of spontaneous emission which registered perpendicular to a laser axis are shown in Fig.1 for a mixing ratio Ar/excimer of 40/60 and different pressures. The peak at λ = 248 nm corresponds to the KrF laser transition and the broad-band emission from 350 to 500 nm is emitted from Kr2F * molecules and the low intensity peaks in the region λ > 750 nm are ArI and KrI atomic lines.