For a thin layer of thickness d<l(coherence), we have observed a nonli
near Brewster angle in transmission by time-resolved second-harmonic (
SH) generation. The associated nonlinear polarization is different fro
m zero and oscillates in the plane of incidence. We interpret the vani
shing SH signal as the result of a field-induced nonlinear polarizatio
n whose axis of oscillation is directed towards the observer. A nemati
c liquid-crystal mixture, which was contained in a cell whose electrod
e polarity could be switched, served as the sample. [S1050-2947(97)012
11-0].