Dual-tunable terahertz metamaterial perfect absorption device based on optical pumping and temperature control

Abstract

The study develops a dual-tunable terahertz (THz) perfect absorber by utilizing optical pumping to alter the conductivity of photosensitive silicon (Si) and temperature-controlled conductivity of vanadium dioxide (VO₂). The photogenerated carrier effect allows for the modulation of the Si's electrical conductivity when its photosensitive surface is illuminated with a specific wavelength pump light. This enables the dynamic switching of the absorber's properties from narrow-band to broadband absorption. Without pump light excitation, the absorber exhibits dual narrow-band absorption, with two distinct peaks at 12.3 THz and 14.2 THz. Notably, the absorption rate at 14.2 THz exceeds 99%, corresponding to a high quality Q-factor of 710. The application of the pump light leads to a significant increase in the Si's conductivity, which in turn switches the absorber to a broadband absorption mode. In this mode, an absorption bandwidth of 1.5 THz is achieved, with an average absorption rate of 96.2%. To understand the underlying mechanism, we employed three methods: impedance matching theory, electric field distribution analysis, and multipolar scattering decomposition. The narrow-band absorption without pump light is primarily attributed to electric dipole and multipole resonances generated by the combined action of Si and VO₂, as well as specific EQ and TD mode resonances. The increased Si conductivity, when pump light is present, promotes broadband impedance matching between the device and free space. This effect also leads to the formation of new resonant cavities, which results in broadband absorption. The study systematically examined how structural parameters, incident angle, and the environmental refractive index affect the absorption performance. The results show that the system exhibits excellent wide-angle characteristics in the broadband mode with pump light, while it shows angle-sensitive characteristics in the narrowband mode. In the narrow-band absorption mode, it shows high sensitivity to changes in the environmental refractive index, confirming its potential for use as a THz sensor. These findings provide a novel design approach and a solid experimental foundation for creating THz functional devices that are high-performance, multifunctional, and tunable.