Reflection and diffraction of sodium atoms by evanescent laser light fields

Abstract

The reflection of sodium atoms form a mirror formed by a light field consisting of a travelling evanescent wave is reported. The light field is produced by total internal reflection of a laser at a quartz/vacuum interface. Specular reflection was observed for laser detunings of several GHz from the sodium D-line resonances, and for atoms incident at angles of up to 3 milliradians. No evidence of a predicted weaker deflected peak due to internal excitation of the atoms was observed. In a further experiment, a standing wave interference pattern, expected to act as a diffraction grating, was established in the evanescent light field by retroreflection of the laser beam. Reflection of sodium atoms was also observed in this configuration, but the angles of incidence for which a reflected beam could be detected were too small to produce measurable diffracted beams. However, the range of laser frequencies for which reflection occurred was found to be more than twice as large as that for the simple travelling wave atomic mirror. This result is in qualitative agreement with model calculations for the standing evanescent wave interaction.