Efficient optical pumping of alkaline atoms for evanescent fields at dielectric-vapor interfaces

We experimentally demonstrate hyperfine optical pumping of rubidium atoms probed by an evanescent electromagnetic field at a dielectric-vapor interface. This light-atom interaction at the nanoscale is investigated using a right angle prism integrated with a vapor cell and excited by evanescent wave under total internal reflection. An efficient hyperfine optical pumping, leading to almost complete suppression of absorption on the probed evanescent signal, is observed when a pump laser beam is sent at normal incidence to the interface. In contrast, when the pump and probe beams are co-propagating in the integrated prism-vapor cell, no clear evidence of optical pumping is observed. The experimental results are supported by a detailed model based on the optical Bloch equation of a four atomic-level structure, which also includes a treatment of transit relaxation and wall collision with relaxation rates that were obtained directly from the thermal velocities of the atoms and the penetration depth of the evanescent wave. The obtained highly efficient optical pumping at the nanoscale is regarded as an important step in the quest for applications such as optical switching, magnetometry, and quantum memory.