Ga nanoparticle monolayers formed by evaporation-condensation in ultrahigh
vacuum and embedded in a transparent SiOx matrix generate second harmonic (
SH) signals in transmission and reflection when illuminated by a 150 fs, 80
0 nm laser pulses. The observed SH light exhibits a critical dependence on
input and output polarizations, angle of incidence and azimuthal orientatio
n of the samples. The results lead to a consistent picture of shape and ori
entation of the nanoparticles. Linear transmittance spectra in the visible
range support these findings and the observed size dependence of the SH sig
nal.