Z-scan Characterizing Technique And Optical Nonlinear Properties Of A Disperse Yellow-7 Films

The Z-scan technique is a very important yet simple method for characterizing the optical nonlinearities, and can measure the magnitudes and signs of the imaginary (Im[χ³]) and real (Re[χ³]) parts of third-order susceptibility (χ³) simultaneously. On the basis of profile of different input beam influence to Z-scan measurement sensitivities, using numerical methods to simulate transmittance curves of Z-scan. In contrast to different transmittance of input beam and top-hat influence to sensitivities of Z-scan measurements. Among three input beam, the best measured sensitivity of Z-scan is Gaussian-Bessel beam. Secondly, is Gaussian beam. Airy-spot beam is the lowest. But Gaussian-Bessel beam can't gain easily in the course of experiments. Generally, top-hat beam was applied in experiments. As for top-hat beam and transmittance of 0.1-1.0 of Gaussian beam intercepted aperture, they were measured to transmittance curves of Z-scan. We find that sensitivities of Z-scan measurements were improved by changing radius of aperture at different transmittance of input beam. When studying optical nonlinearity of a disperse yellow-7 thin films, we find that a disperse yellow-7 thin films not only has the third-order optical nonlinearity, but also the fifth-order optical nonlinearity can't neglect. In the case of analysis the mechanism of the optical nonlinearity of a disperse yellow-7 thin films, using efficient numerical simulation methods to distinguish the third-order and fifth-order optical nonlinearities on theory. We investigated, as a test, the third-order and fifth-order optical nonlinearities of a disperse yellow-7 thin films by the use of the top-hat beam Z-scan technique, with 35-ps-duration pulses at a 1064-nm wavelength, Nd:YAG dye laser. For the material with the fifth-order optical nonlinearity, many different intensity Z-scan measurements are necessary. A disperse yellow-7 thin films was measured, The results show that if peak-valley distance of Z-scan curves, then the third-order nonlinear refraction coefficient and the fifth-order nonlinear refraction coefficient are the same signs. If peak-valley or valley-peak structure of Z-scan curves is converse, then the third-order nonlinear refraction coefficient and the fifth-order nonlinear refraction coefficient are the opposite signs. In experimental measurements, Z-scan curves maintains single valley-peak structure, and height of peak or depth of valley depends on increasing of beam intensity is decreased.