Sub-Doppler Fluorescence Spectroscopy in Thin Gas Cells Pumped with Broadband Radiation

Excitation of atoms (molecules) of a rarefied gas by stationary broadband optical radiation in a thin cell with an inner thickness many times smaller than the transverse size is studied theoretically. The features of the optical pumping and transit-time relaxation of atomic particles in such cells open new possibilities for ultra-high-resolution spectroscopy. The conditions under which narrow high-contrast sub-Doppler fluorescence resonances arise at the central frequencies of spontaneous transitions from optically excited atomic (molecular) quantum levels are analyzed.