Enhanced optical nonlinear absorption of graded Au--TiO2 composite films

This paper reports that single-layer and graded Au--TiOAu--TiOAu--TiO$_{2}$ granularcomposites, graded composite films, $Z$-scan, optical nonlinearabsorptionProject supported by the NationalNatural Science Foundation of China (Grant No 10474075).4270, 7820This paper reports that single-layer and graded Au--TiO$_{2}$granular composite films with Au atom content 15{%}--66{%} wereprepared by using reactive co-sputtering technique. The third-orderoptical nonlinearity of single-layer and graded composite films wasinvestigated by using s- and p-polarized $Z$-scans in femtosecondtime scale. The nonlinear absorption coefficient textit{$beta$}$_{rm eff}$ 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 atomcontent 15{%}--66{%}. The textit{$beta $}$_{rm eff}$ value ofthe 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 textit{$beta $}$_{rm eff}$of single-layer films. Broadened response in the wavelength region730--860,nm of the enhanced optical nonlinearity of gradedAu--TiO$_{2}$ composite films was also investigated.