MEASUREMENT AND MODELING OF INTENSITY-DEPENDENT ABSORPTION AND TRANSIT RELAXATION ON THE CESIUM D-1 LINE

The intensity dependent absorption was measured on the D-1 line (6S(1/ 2) --> 6P(1/2) transition) in atomic cesium. The magnetic field applie d to the vapour and the spatial cross section of the laser beam were c ontrolled and varied during data collection. A three-level rate equati on model is presented in an attempt to explain the results. We show th at this well known approach does not sucessfully model the data obtain ed in the absence of a magnetic field. Hence, a more complex and compl ete model that explicitly includes all of the hyperfine magnetic suble vels (a multilevel model) is presented. This approach accurately model s all of the data collected. The good agreement betweeen this model an d the data allows the determination of the transit relaxation rate (du e to atomic time of flight through the laser beam), Gamma(t) = (1.13+/ -0.20)upsilon(rms)/D, where upsilon(rms) is the two-dimensional root-m ean-squared speed of the atom and D is the FWHM of the Gaussian laser beam spatial profile.