Effect of temperature on nonlinear optical properties of composite media with shape distribution

The temperature dependence of the effective nonlinear optical properties is investigated in random metal/dielectric composites with a shape distribution of particles through the spectral representation. We adopt the Maxwell-Garnett model with a uniform shape distribution and obtain an analytical expression for the spectral density function. Numerical results show that the optical nonlinearity enhancement decreases with the increase of temperature, accompanied by a slight blueshift of the resonant peak. Such a temperature dependence results from the following changes: the conduction electron scattering frequency (due to electron-electron and electron-phonon interaction) and the plasmon frequency (due to the expansion of metal) with the temperature. We find that the former change plays a more important role in understanding the temperature-dependent optical nonlinearity. Moreover, exact results in the dilute limit show a larger magnitude and a more rapid decrease of the optical nonlinearity with temperature, in comparison with the predictions of the mean field approximation. Our results indicate that by decreasing the temperature, it is possible to achieve a large optical nonlinearity. (C) 2002 American Institute of Physics.