Selective reflection of a laser beam from a dilute rubidium vapor.

We study the selective reflection of the laser beam from rubidium atomic vapor at the D2 line (wavelength λ = 780 nm) at different atomic densities. We use a tunable free-running diode laser. We observed a measurable signal at a low atomic density N when the mean distance between resonance atoms reached two wavelengths. In our experiment, the dimensionless parameter N1 /3 λ varied from 0.5 to 2.8. The reflectivity increased with density monotonically. It is interesting to perform experiments when the parameter N1 /3 λ ≪ 1. [ABSTRACT FROM AUTHOR]