Nonlinear Optical Switching and Enhanced Nonlinear Optical Response of Au−CdSe Heteronanostructures

Abstract

The metal−semiconductor heterostructures have recently emerged as a new class of functional materials for their potential applications due to plasmonexciton interactions. Here, we demonstrate the nonlinear optical switching and enhanced nonlinear optical response of Au−CdSe heterostructures. The nonlinear optical properties of CdSe quantum dots and Au−CdSe heteronanostructures are investigated by using a Z-scan technique at 532 nm picosecond laser pulses, and 800 nm femtosecond laser pulses. Interestingly, we observe switching behavior from saturable absorption (SA) to reverse saturable absorption (RSA) with increasing laser intensity. The effective two-photon absorption cross section (σeff) of Au−CdSe heteronanostructures is greatly enhanced which is attributed to charge transfer between CdSe and Au nanoparticles. The nonlinear refraction changes its sign from positive to negative nonlinearity at higher intensities for Au−CdSe heterostructures. Third order nonlinear optical susceptibility is being measured by using the DFWM technique at 532 nm. Similar switching behavior is observed in Au−CdSe heteronanostructures at nonresonant excitations (800 nm), where a CdSe quantum dot shows reverse saturable absorption behavior attributed to the two-photon absorption. The optical switching behavior of these heterostructures could play a potential role in photonics and optoelectronic applications.