Pantoscopic and temperature-controlled dual-band perfect absorber based on strontium titanate material

A nearly perfect dual-band deep sub-wavelength scale and temperature-controlled terahertz absorber is theoretically investigated. The absorber is composed of a periodic metal-dielectric stack array placed on a metallic substrate. Simulation results show that there are two distinct absorption peaks located at frequencies of about 0.140 THz and 0.192 THz in the spectra line under room temperature T = 300 K, and their maximum absorption rates are respectively 99.133% and 98.251%. It is also found that the period of the unit cell is less than 8.97% of the minimum resonant wavelength, which means the deep sub-wavelength absorber structure. Furthermore, it is shown that the proposed absorber is polarization-insensitive, and has good tolerance to the incident angle for both TE and TM wave, i.e., it is pantoscopic for the incident light. Meanwhile, when the temperature changes from 200 K to 400 K, the absorption of the two peaks did not change significantly within the considered frequency range, but the resonant frequency of the two absorption peaks will have a clear blueshift. The effect of structural parameters on the absorbing performance have also been discussed. This work provides a new idea for the design of frequency-agile deep sub-wavelength scale perfect THz absorbers, and the design scheme may be easily extended to the near ultraviolet, optical, infrared, terahertz and millimeter-wave regions.