Active-Thermal-Tunable Terahertz Absorber with Temperature-Sensitive Material Thin Film

ABSTRACT It is shown that active-tunable terahertz absorbers can be realized in a sandwich-structured system comprising an ultrathin dielectric film (polyimide) on a temperature-sensitive substrate (InSb) with a metal film on the back by utilizing the intrinsic carrier density (N) variation in InSb. When increasing the temperature from 250 to 320 K, N in InSb varied from ~ 5.50 × 1015 to ~ 2.98 × 1016 cm-3. Fixing the thickness of dielectric film with the value of 1.37 μm, the absorption peak shifted from 1.41 to 3.29 THz while keeping absorption higher than 99%. This active tunability can respond to even a slight temperature perturbation, and shows polarization insensitivity as well as high tolerance of incidence-angle (absorption peak can still exceed 90% even the incidence angle reaches 60°). Besides, the refractive index of polyimide (PI) has thermal stability at the terahertz range and the merit of good workability. These characteristics guarantee the stability of active-tunable performance. The peculiarities and innovations of this proposal promise a wide range of high efficiency terahertz devices, such as thermal sensors, spatial light modulators (SLMs) and so on.