  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 a
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 optical Bloch
equation of a four atomic levels structure. The obtained on-chip 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.
