Perfect metasurface absorbers play a significant role in imaging, detecting, and manipulating terahertz radiation. We utilize all-dielectric gratings to demonstrate tunable multi-band absorption in the terahertz region. Simulation reveals quad-band and tri-band absorption from 0.2 to 2.5 THz for different grating depths. Coupled-mode theory can explain the absorption phenomenon. The absorption amplitude can be precisely controlled by changing the pump beam fluence. Furthermore, the resonant frequency is sensitive to the medium’s refractive index, suggesting the absorber may be of great potential in the sensor detection field. The experimental results exhibit a high detectivity of pesticides.
In this work, we numerically demonstrated a single narrow band THz absorber based on cylindrically shaped periodical p-type doped silicon with excellent attributes, including polarization insensitivity and optical tunability. Good absorption characteristics were demonstrated at 0.57 THz with an absorption of nearly 99.75% and a quality factor of 11.278. Furthermore, its absorbance could be flexibly tuned from above 99% to less than 35% by changing the pump beam fluence from 0 µJ/cm2 to 3000 µJ/cm2. The demonstrated tunability may find potential applications in dynamic functional THz devices.
The design, characterization, and experimental demonstrations are presented for triple-band, near-perfect, composite metamaterials that absorb in the terahertz regime. Three absorption peaks are observed at 0.537 THz, 0.948 THz, and 1.59 THz with the respective absorption coefficients of 0.957, 0.988, and 0.96. The effect of spacer thickness on absorption is analyzed with interference theory, and the conditions for unity absorption are obtained via comparison of amplitude and phase. The effect of the length (l) of four outer parts of Jerusalem cross on the absorption is analyzed via transmission line theory. Furthermore, the absorption effects of capacitance and inductance caused by the changing l are examined. The calculated multi-band transmission line model corresponded well to simulations. The effect of the outside length on the absorber performance is further explained by electric field distributions, which is experimentally confirmed. Overall, the consistent conclusions provide design guidance for metamaterial absorbers, or the realization of tunable absorbers, and provide a further understanding of the mechanisms.
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