Stegeman figures for 3/sup rd/-order optical nonlinearity in hybrid semiconductor nanocrystal Qot-polymer film

Summary form only given. To be useful in transmissive devices exploiting nonlinear phase change such as nonlinear directional couplers and optical limiters, the material must provide a /spl pi/ phase change before the optical power exciting the phase change is substantially absorbed. The Stegeman figures of merit W and T/sup 3/ quantify this requirement. The Stegeman figure of merit relating to linear absorption, T, has a substantial technological component inside inhomogeneous (hence scattering) materials, including the hybrid polymer-nanocrystal materials considered herein. We have sought new chemical routes to ensuring a uniform dispersion of nanocrystals inside the polymer even at high nanocrystal concentrations. We prepared CdS nanocrystals in aqueous solution using thiols as stabilizer. The nanocrystals were transferred from aqueous to organic phase, homogeneously mixed with PMMA, and processed into solid films. Measured fractional transmission and scattering spectra are shown for a 200 /spl mu/m thick film. In pure PMMA, absorption is strong only below 380 nm. Doping with semiconductor nanocrystals introduces strong absorption around 480 nm and below. Above 500 nm, scattering dominates loss. The decrease in scattered intensity with wavelength is consistent with Rayleigh scattering.