Optical behaviour of nematic liquid crystal doped with carbon dot in the nonlinear optical regime

Abstract

We delve into the effect of carbon dot (c-dot) doping at different concentrations (0.1, 0.2, 0.4, and 1 wt%) on the third order nonlinear optical properties of a nematic liquid crystal (NLC). C-dots were synthesized by the thermal decomposition of ammonium citrate salt. The size and morphology of prepared c-dots were confirmed by the TEM micrograph. Nonlinear optical properties of c-dot doped liquid crystal were investigated by the z-scan method using a Q-switched Nd: YAG laser delivering 7 ns pulse at 532 nm wavelength. A phenomenal increase in the nonlinear absorption coefficient, βeff, was observed for 0.2 wt% c-dot doped liquid crystal. There is an enhancement in the value of third order susceptibility, χ(3), of the order of 10 for the doped liquid crystal. An increase in the third order nonlinear optical absorption coefficient implies a better optical limiting characteristic than the pristine LC. The optical limiting threshold value of 0.2 wt% c-dot doped LC is found to be 1.23 J/cm2. We determine for the first time that c-dot doping in NLC leads to a significant improvement of the nonlinear optical properties compared to pure LC. The results indicate that the system under study could be a promising candidate for nonlinear photonic devices and optical limiters.