Electro-optic effect and optical rectification in gold nanoparticles immobilized above a gold surface

Second-order nonlinear optical effects, a linear electro-optic (EO) effect and optical rectification (OR), were observed in surface immobilized gold nanospheres (SIGNs) above a gold surface with a gap of about 1.4 nm. The EO and OR measurements were performed in an attenuated total reflection geometry under a surface plasmon resonance condition. While it has been reported that the SIGN structure shows considerable second-harmonic generation activity, there has been no report on a linear EO effect and OR in the SIGN structure. The effective second-order susceptibilities of a single SIGN structure were evaluated to be 13 pm V_-1 (EO) and 40 pmV_-1 (OR). Although the theory predicts that the susceptibilities of EO and OR will be equal, the observed susceptibilities were different. The reasons for this discrepancy are discussed.