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6 July 1994 Z-scan measurement on liquid crystals using top-hat beams
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The conventional Z-scan technique using Gaussian beams for measuring intensity dependent optical nonlinearities is extended to allow the use of beams with top-hat profile. Potential applications of the top-hat beam Z-scan technique include the measurement of (chi) (3) over a wide spectrum which typically requires the use of a dye laser. We present a graphical method which allows straightforward determination of both the real and imaginary components of (chi) (3) from Z-scan data. Using the top-hat Z-scan scheme, we have measured (chi) (3) as function of wavelength for typical liquid crystal materials, over the visible spectrum. The spectral behavior of (chi) (3) gives insight into the underlying physical process on various time scales. We also present results of pump-probe measurements of the nonlinear absorption coefficient of the nematic liquid crystal 5CB. Our results indicate that the nonlinear absorption process in the nanosecond time regime is dominated by the two-photon excited-state absorption process. The time constant of this process is estimated from experimental data. A simple model is presented which agrees with our observations.
© (1994) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
W. Zhao, Julie H. Kim, and Peter Palffy-Muhoray "Z-scan measurement on liquid crystals using top-hat beams", Proc. SPIE 2229, Nonlinear Optical Materials for Switching and Limiting, (6 July 1994);

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