We present experimental data for the irradiance dependence of the optical nonlinearity of an organic material at different wavelengths across resonance. The material studied was a suspension of vanadyl-phthalocyanine nanocrystals in cyclohexane. The refractive and absorptive contributions to the nonlinearity were resolved by use of the z-scan technique with a tunable picosecond laser source. The observed dependence of the nonlinearity with irradiance is explained by excited-state absorption, and a three-level model is used to describe the nonlinear response. A fit to the experimental data is made, allowing the extraction of molecular parameters that are of interest for a full characterization of the nonlinearity.
© 2000 Optical Society of America
(070.4340) Fourier optics and signal processing : Nonlinear optical signal processing
(160.4330) Materials : Nonlinear optical materials
(190.4710) Nonlinear optics : Optical nonlinearities in organic materials
R. Rangel-Rojo, H. Matsuda, H. Kasai, and H. Nakanishi, "Irradiance dependence of the resonant nonlinearities in an organic material," J. Opt. Soc. Am. B 17, 1376-1382 (2000)