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.