Wall relaxation of spin-polarized sodium measured by reflection spectroscopy.

Using reflection spectroscopy of optically pumped sodium vapor, we have performed what is to our knowledge the first direct measurement of the spatially inhomogeneous spin polarization near a glass surface. On the basis of a theoretical description of the reflection at an inhomogeneous, anisotropic medium, we deduce the magnitude of the small residual magnetization at the surface from an analysis of the optical line shape. This allows us to specify the depolarizing properties of the surface.