Enhanced optical nonlinear absorption of graded Au--TiO2 composite films
Liu Li(刘莉)a)b)† and Su Xiong-Rui(苏雄睿)b)
a College of Electronics & Information Engineering, Wuhan University of Science and Engineering, Wuhan 430073, China; b Department of Physics, Wuhan University, Wuhan 430072, China
Abstract This paper reports that single-layer and graded Au--TiO$_{2}$ granular composite films with Au atom content 15%--66% were prepared by using reactive co-sputtering technique. The third-order optical nonlinearity of single-layer and graded composite films was investigated by using s- and p-polarized $Z$-scans in femtosecond time scale. The nonlinear absorption coefficient $\beta_{\rm eff}$ of single-layer Au--TiO$_{2}$ films is measured to be --2.3$\times $10$^{3}-$0.76$\times $10$^{3}$ cm/GW with Au atom content 15%--66%. The $\beta_{\rm eff}$ value of the 10-layer Au--TiO$_{2}$ graded film is enhanced to be --2.1$\times $10$^{4}$cm/GW calculated from p-polarized $Z$-scans, which is about ten times the maximum $\beta _{\rm eff}$ of single-layer films. Broadened response in the wavelength region 730--860 nm of the enhanced optical nonlinearity of graded Au--TiO$_{2}$ composite films was also investigated.
Received: 22 October 2007
Revised: 16 November 2007
Accepted manuscript online:
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