ELECTRONIC-ENERGY TRANSFER IN A DENSE LEVEL SYSTEM

The fluorescence spectra induced by resonant laser excitation of a vapor mixture containing four alkali atoms have been detected and analyzed. These spectra show a large number of atomic lines due to collisional energy-transfer processes between laser-excited atoms. The ratio of the directly-excited lines to the collisionally-populated lines increases by orders of magnitude when the number of atomic species in the mixture is increased. A model is proposed which gives the right order of magnitude for the observed line populations and permits a detailed analysis of rather complex conditions. The model shows that for a fixed total laser-power density, the internal energy of the vapor mixture may be increased by exciting all of the atomic species and that it is possible to store in the vapor mixture a high fraction of the laser energy.