Mechanically Tunable Terahertz Metamaterial Perfect Absorber

The development of a wide range of technologies based on terahertz (THz) electromagnetic radiation drives a strong demand for flexible optical elements. Metasurfaces based on metallic resonators offer a versatile toolkit that permits easy tuning over a wide spectral range by the geometric design. Herein, a mechanically tuned metasurface perfect absorber comprised of split‐ring resonators in combination with a metallic mirror in a microcavity arrangement, is demonstrated. By mechanically tuning the length of the microcavity in the range of 10 μm and above, precise control over the perfect absorption condition is exhibited. A maximum recorded extinction of 45.8 dB is obtained at the perfect absorption condition, corresponding to a suppression of the reflected radiation by almost five orders of magnitude. Experiments are performed in a reflection arrangement using a terahertz time‐domain spectrometer. Simulations of the experimental arrangement show that near‐field effects are weak and the enhancement of metamaterial perfect absorption is in agreement with purely interferometric effects.