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

We present an experimental study of nonlinear selective reflection at a dielectric-Cs-vapor interface, in a three-level cascade-up scheme. T he nonlinear reflection at the Cs D-2 resonance line is monitored in t he presence of resonant irradiation at 621 nm or 658 nm (6P(3/2) --> 8 D(5/2),9S(1/2)). Experimental reflection spectra with either counterpr opagating or copropagating light beams are analyzed and compared with the theoretical predictions of F. Schuller et al. [Phys. Rev. A 47, 51 9 (1993)]. For a blue-detuned pump and copropagating geometry an alter native type of three-level coherent reflection resonances, specificall y associated with desorbing atoms, is observed. Also observed is the n onlinear reflection associated with the off-resonant, two-photon dispe rsion of atoms moving parallel to the window surface. Probe beam satur ation is responsible for the appearance of additional resonant feature s in reflection spectra. Finally we analyze crossover spectral resonan ces which arise from nondegenerate, four-wave-mixing processes induced by the combined influence of counterpropagating pump and probe beams, and the pump beam being partially reflected by the window.