Contibution of Hexagonal-like Structure to the Nonlinear Optics in Large-sized SiC Nanocrystallites
Résumé
Contribution of the hexagonal-like structure to the optically poled (photoinduced) second harmonic generation (SHG) in SiC large-sized nanocrystallites (with sizes within the 10-30 nm) incorporated into the oligoetheracrylate photopolymer matrices is found. The SHG measurements have been carried out using pulsed YAG:Nd laser ( @ duration time = 1550 ps, laser power about 30 MW) as probing ones and a nitrogen pulse laser ( P = 10 MW; ; = 0.377 m; = 515 ps) as a photoinducing beam. We have found that with increasing pumping power the SHG output signal increases and achieves its maximum value at the pump photon power about 2.6 GW/cm 2 per pulse. The maximal output photoinduced SHG signals have been observed for parallel polarization between the pumping and probing light beams and the observed maximal value of the SHG is equal about 4.02 pm/V. With decreasing temperature the SHG signal considerably increases below the 30 K. Probe-pump measurements show an existence of the photoinduced SHG maximum at the delaying time equal about 18-22 ps. The performed molecular dynamics simulations and band structure calculations allow to find a relation between nanocrystallite size dimensions, band structure and degree of hexagonality (partial presence of the hexagonal structural component). An increase of the SHG signal is correlated well with increasing degree of hexagonality.