Flux measurements of alkali atoms diffusing via multiple surface scattering in asilanated glass tube

Abstract

Alkali atoms that are diffusing away from a source via multiple surface scatteringin a nonstick coated glass tube are monitored by laser fluorescence. Densitiesare measured by fluorescence intensity and weak-field absorption, andsmall asymmetries in the line shape provide a measurement of the flux.Average velocities as small as 0.3% of the thermal velocity can be resolvedusing the technique presented. Model calculations are presented and fitto the data, providing approximate values for the sticking probability,and the probability of specular scattering versus diffuse scattering(related to momentum accommodation). For the silane-based coatingSurfaSilTM,we find that the scattering is mostly diffuse, and that the sticking probability is ofthe order of 10−4 or 10−3. With refinement, the technique can be used to measurethe variation in the sticking probability along the length of the tube, which couldbe useful for studying and improving gas separation columns. We presentnumerical calculations of surface light-induced drift (SLID) effects, but noevidence for SLID is observed experimentally.