Optically controlled and polarized sensitivity adjustable terahertz metamaterial absorber

A photoactive terahertz (THz) absorber is designed based on the quadruple rotational symmetrical metamaterial structure combined with the GaAs bars. For the bare metallic metamaterial structure, the THz absorber shows a polarization insensitive property with two perfect absorption peaks at 0.62 THz and 0.84 THz, and the absorption rates are 98.80 % and 99.97 %, respectively. For the GaAs functionalized metamaterial structure, the hybrid THz absorber is equivalent to the metallic resonator in the absence of the pump light since the GaAs bars are in an insulated state with the conductivity of 100 S/m. Further, the GaAs bars turn into a metallic state as the conductivity increases to 5 x 105 S/m under pump light. The hybrid THz absorber becomes an axisymmetric structure with a polarization sensitive property, which could excite two new perfect absorption frequencies at 0.71 THz and 2.24 THz, and the corresponding absorptivity are 99.80 % and 99.90 %. The simulated electronic field distribution and surface current distribution indicate that the perfect absorption is due to the dipole resonant modes. The proposed optically controlled and polarization tunable THz metamaterial absorber provides potential applications in the related fields of THz switches, detectors, and imaging.