Nonlinear Optical Properties of Au Colloid-Doped Glasses
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NONLINEAR OPTICAL PROPERTIES OF Au COLLOID-DOPED GLASSES KOHEI KADONO, TORU SAKAGUCHI, HAJIMU WAKABAYASHI, HIROSHI YAMANAKA, MASARU MIYA AND HIROSHI TANAKA Government Industrial Research Institute, Osaka, 1-8-31, Midorigaoka, Ikeda, Osaka 563, Japan.
TOSHIO FUKUMI,
ABSTRACT Degenerate four-wave mixing experiments have been performed for Au colloid-doped glasses prepared by melting and sputtering methods. The nonlinear optical properties of the glasses are discussed from viewpoint of the concentration of the Au colloid particles and the thickness of the glasses. We also discuss the dependence of the nonlinear properties on the pulse duration of laser for the measurements, and a very slow relaxation. INTRODUCTION Optical nonlinear properties of metal colloid particles embedded in glass or polymer matrices, or suspended in solutions have received much attention because of the large nonlinearity[l-lO]. Particularly, for the systems of Au colloid particles, active investigations are ongoing since the early report in this area[2]. This is due to the fact that a lot of studies on the linear optical properties of Au colloid solutions and Au colloid-doped glasses have been performed[ll] and that these materials have absorption at the region of wavelength, the laser pulse of which is readily available. Therefore, the Au colloid systems are regarded as a model material for the study on the mechanism of the nonlinear properties of small metallic particles or colloid. Hache et al. proposed three mechanisms for the nonlinearity in their comprehensive paper[3], i.e., the contribution of the intraband transition, the interband transition and the hot electron excitation. From experiments using various Au colloid-doped glasses, it was concluded that the contribution of the interband transition and the hot electron excitation dominant the intraband transition; it has been revealed that the nonlinearity is size independent though the intraband transition mechanism theoretically predicts the strong size dependence. The size independent feature of the nonlinearity has been also confirmed for colloidal solutions[7]. On the other hand, we have carried out the preparation of Au colloid-doped glasses including large amount of particles in order to obtain materials with high optical nonlinearity. Since the solubility of gold in glass melt is small, it is difficult to disperse large amount of Au colloid particles in glasses prepared by conventional melting method. In this method, gold compounds are dissolved in the glass melt and after the glassification of the melt, colloid particles are grown by annealing process of the glass matrix. In contrast, the sputtering method and ion-implantation have been successfully used for the preparation of glass films doped with very large amount of Au atoms[1215]. The volume fraction of Au colloid particles is higher by 3 to 4 orders than that of glasses prepared by melting method. This means that the Au colloid particles become very close to each other; the distance between the neighbouring Au colloid pa
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