Photocontrolled ultra-broadband metamaterial absorber around the terahertz regime.

In this paper, we innovatively stack multiple resonant units of photoconductive silicon to design an ultra-broadband metamaterial absorber. By manipulating the conductivity of the silicon with a pump beam, adjustments are made to the amplitude of the wide absorption spectrum spanning 6.6 THz, enabling functional switching from total reflection to near-perfect ultra-broadband absorption. By integrating vanadium dioxide as an intermediary layer, a dual-mode switchable absorber is realized, offering dual control functionalities. Temperature changes enable the absorber to switch between dual-band absorption and ultra-broadband absorption, while variations in pump beam intensity allow for further amplitude adjustments within the absorption spectrum. Impedance matching theory and near-field analysis provide the necessary physical foundation for understanding broadband absorption. Structural parameters, incident angle, and polarization angle of the incident electromagnetic waves are also studied to demonstrate the device's robustness. Our proposed absorbers not only greatly broaden the absorption bandwidth of silicon-based absorbers, but also offer versatility, polarization insensitivity, and robustness over a wide range of incidence angles. Moreover, our design ideas are useful for broadening the bandwidth and enhancing absorption, which enables wider applications in ultra-broadband terahertz absorption and promises extensive prospects.