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 $500\mu \mathrm{m}$. 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 ${\tau }_s=0.53\pm 0.03\mu \mathrm{s}$ at a cell wall temperature of $103°\mathrm{C}$. The temperature dependence of ${\tau }_s$ is fitted to ${\tau }_s={\overline{\tau }}_0\exp (E_a/kT)$, yielding a preexponential factor ${\overline{\tau }}_0={2.2}_{-1.4}^{+5.1}\mathrm{ns}$ and an activation energy $E_a=0.19\pm 0.03\mathrm{eV}$.

• Received 12 November 2008

DOI:https://doi.org/10.1103/PhysRevLett.103.073201