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Acta Physica Sinica

Optical bistability in granular composite media at high temperatures*

Lu Xingzhong, Gao Lei, (1)苏州大学物理科学与技术学院,苏州　215006; (2)苏州大学物理科学与技术学院,苏州　215006 常州工学院理学院,常州　213002

Published Jan 1, 2004• 0 citations
Publisher

Abstract

Optical bistability has been investigated in granular metal-dielectric composite media at high temperatures. Based on Maxwell-Garnett approximation and the spe ctralrepresentation, we calculate numerically the electric field as a function of the applied electric field E２０,and thus the opticalbistability can be studied.We show that the width of optical bistability decreases with increasing temperature.Furthermore, we study the dependence of the refractive index and the extinction coefficient on the temperature.

DOI
10.7498/aps.53.4373

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Optical bistability has been investigated in granular metal-dielectric composite media at high temperatures. Based on Maxwell-Garnett approximation and the spe ctralrepresentation, we calculate numerically the electric field as a function of the applied electric field E２０,and thus the opticalbistability can be studied.We show that the width of optical bistability decreases with increasing temperature.Furthermore, we study the dependence of the refractive index and the extinction coefficient on the temperature.
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We studied the intrinsic optical bistability(OB) of coated spherical particles with graded dielectric profiles.According to Maxwell equations, we obtained the spatial average of the local field in the core as a function of the external applied field. Numerical results for power-law graded profiles show that the optical bistable behavior is dependent on the shell thickness and the power-laws exponent k. The interval of optical bistability increases with increasing shell thickness or increasing k. In addition, the field-dependent reflectance at normal incidence R in random composites is also investigated, and a hysteretic loop is observed.
The mean-field approximation method is proposed to investigate the intrinsic optical bistability in nonlinear composite media, which consists of nonlinear metallic granules embedded in nonlinear dielectric host. The effect of nonlinear susceptibility on the bistable behavior is analyzed. It is found that nonlinear metallic granules and nonlinear host medium have different effects and the nonlinearity of metallic granules is more effective in minimizing the threshould value of the bistable behavior. We also investigate the effect of the shape factor of metallic granules on the threshold value.
Abstract Optically bistable behaviour is demonstrated for systems consisting of optically nonlinear microcrystallites embedded in an optically linear metal or dielectric. The most simple version of the local‐field correction serves as feedback mechanism thus avoiding external mirrors. The dielectric function for macroscopic samples is calculated with Garnett's effective medium theory. Numerical examples for the reflectivity and the transmissivity are given for an embedded dielectric with exciton‐like nonlinearity.
We examine the nonlinear dielectric response of small spherical grains ϵ m embedded in a linear dielectric ϵ d . The models for the spherical grains are a Kerr medium1,2 and a two-level system.3 The expression for the dielectric function ϵ m is dependent of the grain size; in addition it also depends on the local electric field E L . This field is related to the external applied field E0 by the equation E L = (3ϵ d /ϵ m + 2ϵ d )E0. The steady-state equation for the averaged external field is ∇2E0 + (ω2/c2)ϵ*E0 = 0, where ω is the frequency of the field, ϵ* is the dielectric function from the effective medium approximation, and it is obtained from the self-consistency relation4 〈ϵ(r) − ϵ*/ϵ(r) + 2ϵ*〉 = 0; the angular brackets denote an average taken over the ensemble of dielectric spheres distributed in a small volume. Using the slowly varying-envelope approximation we solve these equations for a distribution of grain radii and the affect this has on the effective optical nonlinearities. In particular, we show its effect on the optical bistability for these composite systems.