SELECTIVE REFLECTION FROM A VAPOR OF 3-LEVEL ATOMS

We study internal selective reflection from a dielectric-vapor interfa ce, where three levels of the vapor atoms in a LAMBDA configuration ar e connected by two light frequencies. The reflectivity contains then b oth a sub-Doppler structure due to spatial dispersion in the boundary layer and the dark resonance arising from coherent population trapping . We derive analytical expressions for the reflectivity of either one of the two light beams. The contributions from atoms approaching or le aving the interface are strongly different, whereas they are identical for the case of two-state atoms.