Second- and third-harmonic generation in silicon
carbide (SiC) nanopowders embedded in a polymethyl methacrylate
(PMMA) film are studied using nano-, pico-, and femtosecond
laser pulses. Second- and third-harmonic generation processes are
shown to allow the detection of absorptive agglomerates of
nanocrystals in transparent materials and the visualization of
optical breakdown in nanocomposite materials. Polarization of the
third-harmonic signal is shown to be highly sensitive to the
polarization of the pump field, permitting third-harmonic
generation to be used as a probe for the anisotropy of
nanocomposite materials. The second-harmonic signal, on the
contrary, has no memory of the initial polarization state of the
pump field and is, consequently, ideally suited as a measure of
orientation-averaged nonlinearities of nanopowder materials.