Spectroscopy of Heteronuclear Xenon-noble Gas Dimers – Towards Bose-Einstein Condensation of Vacuum-UV Photons

Other than for the three-dimensonal case of blackbody radiation, low-dimensional photon gases can exhibit Bose- Einstein condensation, as been experimentally demonstrated in the visible spectral regime first in 2010 using a dye-filled optical microcavity [1]. Here a short, wavelength sized spacing of cavity mirrors provides a low- frequency cutoff imprinting a spectrum of photon energies restricted to well above the thermal energy, and photons thermalize by repeated absorption and (re-)emission processes on the dye molecules to room temperature. As a prominent feature, a Bose-Einstein condensate of photons is as a coherent light source. This is of special interest in the vacuum-ultraviolet spectral regime (100 nm-200 nm, VUV), as it is difficult to realize lasers in this wavelength range. This is mainly due to the
$1/\omega^{3}$
-scaling of excited state lifetimes, which requires increasingly high pump powers at short wavelengths to create population inversion in a laser medium.