Study on third-order nonlinear optical properties of the composite films with Ag nanoparticles and CdSe quantum dots

Abstract

Through the process of magnetron sputtering and spin-coating, CdSe/Al2O3/Ag and CdSe/PMMA/Ag composite films were fabricated. All the composite films' linear optical performances, morphology and structure have been concluded. Composite films' nonlinear refraction and absorption properties were investigated by fs Z-scan technique. When the laser energy is increased from 100nj to 500nj, the CdSe/PMMA/Ag composite films' saturated absorption (SA) are enhanced, and the CdSe/Al2O3/Ag composite films are converted from SA to reverse saturated absorption (RSA), the nonlinear absorption behavior can be explained by a three-level model. At 300nj laser energy, all the composite films exhibit SA. Both the composite films' nonlinear refraction and absorption were enhanced with the increasing of Ag nanoparticles (NPs) sputtering power. However, with the layers of CdSe quantum dots (QDs) increasing, the composite films' nonlinear absorption and refractive indexes were both decreased. Moreover, the CdSe/PMMA/Ag composite films’ third-order nonlinear polarization index, as compared with that of the CdSe/Al2O3/Ag composite films, are about ten times higher. Composite films can be used in many types of signal processing as well as in photonics and optoelectronic applications.