Generation of the second and third harmonics of femtosecond Cr: forsterite laser pulses in SiC/PMMA nanopowder films

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