3-LEVEL NONLINEAR SELECTIVE REFLECTION AT A DIELECTRIC-CS VAPOR INTERFACE

We present an experimental study of non-linear selective reflection at a dielectric/Cs vapour interface, in a three-level caseade-up scheme. The non-linear reflection at the D2 resonance line is monitored in th e presence of a resonant irradiation at 621 nm or 658 nm (6P3/2 --> 8D 5/2, 9S1/2). A novel type of two-photon-induced reflection resonances specifically connected with atoms desorbing from the surface is observ ed. We demonstrate that these resonances allow one to monitor the atom ic-velocity distribution at vapour-solid interfaces.