Selective terahertz absorber for angle and polarization-independent spectral sensing

Polarization- and incident-angle-independent narrow-band terahertz (THz) absorbers were developed to enable THz imaging, radar, and spectroscopy applications. The design comprises a transparent fused silica (SiOx) substrate backed by an optically thick metal layer and topped by a periodic array of metal cross patterns. Finite element analysis (FEA) simulations optimized the geometry of devices fabricated by contact photolithography. Resonances were characterized by Fourier-transform reflectance spectroscopy. The design tunable absorption bands appeared in the range 50-200 cm (1.5-6 THz) with full widths at half maximum of 20-56 cm (0.6-1.68 THz). Maximum absorption was -8.5 to -16.8 dB. The absorption bands are independent of incidence angle and polarization in agreement with simulation.