The diffusion coefficient for rubidium in poly-(dimethylsiloxane) thin films has been determined via pulsed laser depletion and cw laser time-of-flight detection of desorbing atoms. The value of the diffusion coefficient of 1.2 +/- 0.7 x 10(-5) cm(2)/s agrees with a theoretical estimate and is an important quantity for a quantitative understanding of dynamic light-induced atom desorption. (C) 2004 Elsevier B.V. All rights reserved.