<title>Condensed phase exciplexes for short-wavelength lasers</title>

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Emissions from charge transfer states of rare gas halide RgX molecules in rare gas solids and also of alkali halide ions AX combine the known properties of short wavelength, gas phase excimer lasers with high densities of excited states attainable in the condensed phase. In Ar and Ne crystals binary doped with XeF and F<SUB>2</SUB> a XeF density of 10<SUP>18</SUP> cm<SUP>-3</SUP> is prepared. This high density together with a quantum efficiency close to 1 provides large measured gain coefficients between 11.6 and 2.4 cm<SUP>-1</SUP> for the D-X, B-X, C-A and D-X transitions of XeF in Ar and Ne solids, respectively. Lasing with quantum efficiencies up to 14 percent occurs and beams of low divergence of 3 mrad are extracted with interferometric cavities.Inhomogeneously broadened spectral profiles and relaxation oscillations are observed in the C-A laser emission of XeF in Ar. Concerning alkali halides the e-beam excitation of Ne and Ar matrices doped with 0.4 to 0.7 percent CsF or CsCl results in the deep UV emissions located at 196.5 nm, 220.3 nm, and 211.2 nm and also at 227 nm which are ascribed to the B<SUP>2</SUP>(Sigma) <SUB>1/2</SUB>-X<SUP>2</SUP>(Sigma) <SUB>1/2</SUB> and C<SUP>2</SUP>(Pi) <SUB>1/2</SUB>-A<SUP>2</SUP>(Pi) <SUB>1/2</SUB> transitions of the ionic A<SUP>2+</SUP>X<SUP>-</SUP> states, respectively.