Optically Tunable Triple-Band Perfect Absorber for Nonlinear Optical Liquids Sensing

Metamaterial perfect light absorbers have received more attention due to their applications in various fields. In this paper, a metamaterial nanostructure design based on absorption analysis is introduced for the purpose of nonlinear optical liquids sensing which is composed of a sandwich structure of metal-dielectric-metal layer. The nanostructure can display very high absorbance over triple bands at infrared frequencies give rise to large absorbance at different frequencies. The modelling and numerical analysis are carried out using Finite Difference Time Domain (FDTD) method where a genetic algorithm (GA) is used to optimize the geometric parameters of the nanostructure. Numerical simulations show that the proposed perfect absorber with near unity absorbance on all their bands can be tunable designed whereby the dielectric materials of buffer layer, the geometrical parameters of the sandwich nanostructure design, and the polarization of the incident light determine the absorption band of the metamaterial. The triple band perfect absorber is reasonably polarization insensitive and the absorbance remains large even with large angles of incidence. The sensing mechanism of this sensor is detecting changes in the refractive index of the sample environment. This sensor is first optimized for sensitivity using some biomaterial with fixed RI as a sample; this optimized sensor is then used to investigate some nonlinear optical liquid with nonlinear relation in their RI. We achieved a maximum sensitivity of 273 nm/RIU (corresponding to 53 THz/RIU) for Ethanol. This design has considerable potential in similar measurements in various industry such as medical health, and food quality control.