Nonlinear optical authentication of sesame oil using spatial self-phase modulation

The nonlinear optical (NLO) response of commercially available pure-grade sesame oil (SO) and its adulterated versions is investigated by spatial self-phase modulation (SSPM) technique using a Q-switched pulsed Nd: YAG laser at 532 nm. The NL refractive index (n2) of the samples is determined from the SSPM diffraction patterns and the linear refractive index (RI) using the Abbe refractometer. The decrease in n2 with increasing laser power reveals that the NLO response is primarily dominated by thermally induced RI effects. The SSPM measurements of SO samples adulterated with various edible oils are carried out at 700 mW. The n2 and number of diffraction rings decrease systematically with increasing adulterant concentration. The reduction in n2 is attributed to the dilution of the absorbing species in SO, leading to diminished photo absorption and a weaker thermally induced n2 variations. The study unveils SSPM as a surrogate non-destructive optical approach for monitoring adulteration.