<title>Diagnostics of optical nonlinearities: spatial beam distortion technique and its application to semiconductors and novel materials</title>

Abstract

Development of nonlinear refraction diagnostics methods based on spatial beam distortions technique and nonlinear absorption measurements is illustrated with wide-gap semiconductors experimental data. With picosecond Z-scan technique we have studied competitive optical nonlinearities -- intraband direct equilibrium carriers transitions saturation and interband two-photon absorption (TPA) for a α-SiC(6H) crystal, and enhanced state absorption, absorption saturation and TPA -- of epoxy polymer based on diglicidyl ether of bisphenol A in a wide pumping intensities range (10 MW/cm² - 20 GW/cm²) at 532 nm. The complexity of the analysis was dealt with the nonlinearities signatures recognition problem and selection the part of the Z-scan curve which corresponds to the dominant contribution of the proper nonlinear mechanism on the background of competitive others. The TPA coefficient is β = 3.2 ± 0.3 cm/GW for the α-SiC(6H) crystal. The TPA coefficient is β = 4.0 ± 0.5 cm/GW for the polymer. At very high laser intensities (>7 GW/cm²) photoinduced transformation into some new configuration is taken place that is more absorbent at 532 nm. The TPA coefficient is β = 16.7 ± 3 cm/GW for the photoproduct. Up to pumping irradiance of 20 GW/cm² no optical damage of the polymer was observed.