  Spectroscopy of alkali-buffer gas mixtures at high pressures from
single-digit to several 100 bars in the regime of substantial collisional
broadening is relevant in a wide range of fields, ranging from collisional
redistribution cooling to laboratory astrophysics. Here we report on
spectroscopic measurements of dense rubidium-noble gas mixtures recorded in a
pressure cell equipped with soldered sapphire optical viewports, which allows
for the controlled realization of extreme conditions of high temperature and
high pressure in a table top laboratory experiment. In the gas cell, we have
recorded absorption and emission spectra of rubidium subject to 250 bar helium
buffer gas pressure at 500 K temperature. The spectra to good accuracy fulfill
the thermodynamic Kennard- Stepanov frequency scaling of the ratio of
absorption and emission spectral profiles. Further, the long optical path
length in the cell allowed to both record spectra of rubidium-argon mixtures at
moderate temperatures and high pressures and to observe redistributional laser
cooling in this system.
