Ultrabroad perfect absorption of a graphene-covered compound silver grating for mid-infrared multimolecular identification

Abstract

Abstract Identifying several species of molecules simultaneously is highly desirable but needs more study. We propose an ultrabroad PPA in the mid-infrared based on a graphene-covered compound silver grating (G-CSG) to detect several molecules. Different grooves are composed in one unit and the wide absorption band consists of individual magnetic plasmon resonances (MPRs). The graphene layer enhances the overall absorption without affecting MPRs. The genetic algorithm is applied to search for suitable structure parameters to further enhance the absorption. The average absorption from 3.0 to 6.0 μm is 0.96 for the optimized G-CSG, which is nearly insensitive to the incidence angle. Strong coupling between plasmons and molecular vibrations results into dips in the ultrabroad absorption band. Multiple molecules can be identified simultaneously. Our study provides an efficient way to identify several molecular vibrations at one time, which may be useful in optoelectronics and biology detection.