Spectroscopy of heteronuclear xenon-noble gas mixtures - Toward Bose-Einstein condensation of vacuum-ultraviolet photons

In the vacuum-ultraviolet regime (VUV, 100 - 200 nm), realizing lasers is difficult, as excited state lifetimes scale as 1/ω³, resulting in the need of high pump powers for population inversion. We propose an experimental approach for the realization of a coherent light source in the VUV based on Bose-Einstein condensation of photons. In our group, Bose-Einstein condensation of visible photons is investigated using liquid dye solutions as thermalization media in wavelength-sized optical microcavities, the latter providing a non-trivial energy ground state the photons can condense into.

Conveying this into the VUV, a suitable thermalization medium has to be found. We here consider heteronuclear mixtures of xenon and another noble gas atom, with absorption re-emission cycles on the transition from the atomic ground state (5p⁶) to the lowest electronically excited state (5p⁵6s) and emission from a lightly bound heteronuclear excimer state for thermalization. We report on the results of current spectroscopic measurements, investigating VUV line profiles of samples containing xenon and different noble gases. Also, the data is tested for the validity of the Kennard-Stepanov relation, a fundamental prerequisite for the suitability of a medium as thermalization mediator in the scheme.