Laser energy-pooling processes in an optically thick Cs vapor near a dissipative surface

Abstract

We characterize, for the first time to our knowledge, the laser-induced backward fluorescence (retrofluorescence) spectra that result from energy-pooling collisions between Cs atoms near a dissipative thin Cs layer on a glass substrate. We resolve, experimentally and theoretically, the laser spectroscopic problem of energy-pooling processes related to the nature of the glass–metallic vapor interface. Our study focused on the integrated laser-induced retrofluorescence spectra for the 455.5-nm (72P3/2–62S1/2) and 852.2-nm (62P3/2–62S1/2) lines as a function of laser scanning through pumping resonance at the 852.2-nm line. We experimentally investigate the retrofluorescence from 420 to 930 nm, induced by a diode laser tuned either in the wings or in the center of the pumping resonance line. We present a detailed theoretical model of the retrofluorescence signal based on the radiative transfer equation, taking into account the evanescent wave of the excited atomic dipole strongly coupled with a dissipative surface. Based on theoretical and experimental results, we evaluate the effective nonradiative transfer rate A¯62P3/2→62S1/2sf for atoms in the excited 62P3/2 level located in the near-field region of the surface of the cell. Values extracted from the energy-pooling process analysis are equivalent to those found directly from the 852.2-nm resonance retrofluorescence line. We show that the effective energy-pooling coefficients k˜72P3/2 and k˜72P1/2 are approximately equal. The agreement between theory and experiment is remarkably good, considering the simplicity of the model.