Reexamination of the theory of light-induced atomic desorption

Abstract

The commonly accepted theory of light-induced atomic desorption (LIAD) [S. N. Atutov et al., Phys. Rev. A 60, 4693 (1999)] explains the dynamics of this effect by referring to a light-enhanced diffusion process proceeding in the absorbing medium. On the other hand, recently performed measurements show that in siloxane films which are used in LIAD experiments, the characteristic time of diffusion is extremely short (a fraction of 1 s) compared to the duration of the LIAD effect (hundreds of seconds). This is in contradiction to the conceptual basis of the theory of Atutov et al. that requires the characteristic diffusion time to be sufficiently long. What is more, the theory of Atutov et al. relies on an unjustified assumption about the dependence of the diffusion coefficient on the light intensity. In consequence, the theoretical results of Atutov et al. yield unsatisfactory predictions and do not fit well with experimental data. In this paper, we consider a partially illuminated siloxane-coated cell and propose an alternative theory of LIAD dynamics based on an assumption about lateral diffusion proceeding in the siloxane coating. Our theory provides a unique solution for the desorbed atoms' density regardless of the power of the laser light, explains the lengthy duration of LIAD, and accurately reproduces experimental results. A reasoning which explains how the boundary condition at the siloxane surface is established by the incident light gives us a proper relation between the desorbed atoms' density and the intensity of the desorbing light.