Method for measuring the dwell time of spin-polarized Rb atoms on coated pyrex glass surfaces using light shift

We present a simple method for directly measuring the average dwell time of spin-polarized Rb atoms on coated Pyrex glass surfaces. The method relies on the light shift of the Zeeman resonances of spin-polarized Rb atoms pumped and probed by evanescent waves, and does not depend on the microscopic details of surface interactions. We use a cell whose length is adjustable between 70 and 500 microm. The inverse of the difference between the frequency shifts caused by sigma+ and sigma- pump beams depends linearly on the cell length, from which we obtain the average dwell time tau(s). For a Pyrex glass cell coated with octadecyltrichlorosilane we find that tau(s)=0.53+/-0.03 mus at a cell wall temperature of 103 degrees C. The temperature dependence of tau(s) is fitted to tau(s)=tau[mean](0) exp(E(a)/kT), yielding a preexponential factor tau[mean](0)=2.2(-1.4)(+5.1) ns and an activation energy E(a)=0.19+/-0.03 eV.