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28 June 1999 Transmission measurements of the third-order susceptibility of gold
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Gold nanoparticle composites are known to display large optical nonlinearities. In order to assess the validity of generalized effective medium theories (EMTs) for describing the optical properties of metal nanoparticle composites, we have used the z-scan technique to measure the third-order susceptibility of gold nanoparticle composites across the entire range of fill fractions. These materials range from low concentration statistically random gold sols, to aggregated thin (two-dimensional) composite films, to quasi-bulk thin films above the percolation threshold. These measurements allow the nonlinearity of gold to be determined both directly and by deduction from applicable effective medium theories. We compare our results with predictions which ascribe the nonlinear response to a Fermi-smearing mechanism. We demonstrate that the nonlinear susceptibility changes sign due to a phase shift between the applied field and the local field, and that this sign change occurs at the percolation threshold. Further for films whose thickness is less than an optical wavelength we introduce a 2D form of the Maxwell Garnett model.
© (1999) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
David D. Smith, Yongkwon Yoon, Robert W. Boyd, Curtis E. Banks, and Mark Steven Paley "Transmission measurements of the third-order susceptibility of gold", Proc. SPIE 3793, Operational Characteristics and Crystal Growth of Nonlinear Optical Materials, (28 June 1999);

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