Pantoscopic and polarization-insensitive perfect absorbers in the middle infrared spectrum

Abstract

We have engineered numerically perfect absorbers based on a square ring pattern. The mono- and the multiband perfect absorption were presented in the whole midinfrared region. The characteristic dimension of the single square ring absorber (SSRA), i.e., lattice constant a, can be smaller than 0.1 times the operating wavelength so that the absorber could be viewed as continuous medium. This should be attributed to the high reactance of the patterns, as depicted in an extended equivalent circuit model of our structure. The model can accurately make a prediction of the operating wavelength of the SSRA, and the relative errors can be less than 5%. A crude numerical model of effective permeability was also deduced to account for the magnetic property of the absorbers in the optical spectrum. The multiband perfect absorber exhibited a good stability of polarization, incident angle, and azimuth.