Intense nonlinear optical properties of ZnS quantum dot doped nematic liquid crystal compounds

Abstract

The present work is devoted to the study of third order optical nonlinearity of pure and zinc sulfide (ZnS) quantum dot doped nematic liquid crystal (NLC). The nonlinear absorption and nonlinear refraction properties of pristine and quantum dot doped nematic liquid crystals are discussed. ZnS quantum dots of average size 4 nm are synthesized by chemical co-precipitation method using PVA as a capping agent. The nanostructure of prepared ZnS QDs was confirmed through XRD, TEM, and UV–Visible absorption characterizations. A sensitive, single beam z-scan technique is implemented to determine the nonlinear absorption coefficient and nonlinear refraction coefficient of the samples. The pump radiation is at 532 nm, the second harmonic generation of Q switched Nd: YAG laser having a pulse width of 7 ns and a repetition rate of 10 Hz. The maximum value obtained for third order susceptibility for the 5PCH-ZnS system is 7.07 × 10−10 esu and that for the 5CB-ZnS system is 5.145 × 10−10 esu. The possible mechanisms for the observed nonlinear absorption and refraction are discussed. We observed a notable increase in the optical nonlinearity for the doped system and found to be decreasing at the highest doping concentration under consideration. An optical limiting threshold of 1.99 J/cm2 obtained for the 5PCH-ZnS system indicates that the sample under study can be a potential candidate for optical limiting application.