Extended Model for Saturation in a Two-Level System

Abstract

A model is presented, based on rate equations for a two-level system, which describes both the temporal and time-integrated dependence of the fluorescence signal due to saturation by a broad band and spatially homogeneous laser beam in an optically thin medium. In particular, we discuss the processing of the fluorescence signal by a gated integrator and relations between gate width, laser pulse length, and decay rate constant of the two-level system. It is shown that, even in the relatively simple case of a fully saturating, rectangular laser pulse, the integrated signal is still dependent on atomic and collisional parameters. On the other hand, this dependency can be used to measure these parameters. The only case in which the integrated signal becomes independent of these parameters is the case of a perfectly rectangular portion being sliced out of the time dependent fluorescence signal. An experimental method, which is expected to result in a better approximation of the saturation parameter in the case of the integrated signals, is suggested.