Magnetically trapped spin-polarized atomic hydrogen at ultralow temperatures (T<10 mK) and high densities (n>1013 atoms/cm3) represents the unique realization of a bosonic quantum gas. Temperature and density of the ensemble can be most accurately determined by optical spectroscopy (`Doppler thermometry'). Optical excitation also allows to cool the confined hydrogen gas. Both, optical diagnostics and cooling have been successfully demonstrated at the university of Amsterdam using pulsed one-photon excitation of the Lyman-alpha transition ( 12S - 22P). However, the one-photon transition suffers substantial limitations at temperatures T<1 mK and densities n>1010 atoms/cm3.
We propose a challenging novel approach which overcomes these limitations by two-photon excitation of the 32S/32D excited states. This approach provides a powerful diagnostic tool even in the ultimate regime of Bose condensation which has so far not been accessible to experiments. Furthermore, two-photon excitation offers a new method of optical cooling for a confined dense atomic sample which may allow to reach the Bose regime.