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In this work, we report two multifocal terahertz (THz) lenses (MTLs) based on reflective metasurfaces with focusing efficiencies of 57.3% and 46.3% at a frequency of 3.11 THz, respectively. The reflective metasurfaces were constructed by patterning the polarization-insensitive cross resonator array atop a continuous gold ground plane spaced by a layer of parylene film, which provides a complete 2π phase coverage. The elaborated phase profiles of the two MTLs were arranged based on the Fresnel-Kirchhoff diffraction theory. The two MTLs were theoretically and experimentally verified to converge continuous THz waves into two and four beam spots at their focal planes, respectively. Meanwhile, the MTLs were also experimentally demonstrated with multiple imaging abilities.

Reflective gradient metasurfaces are reported as flat, ultra-thin light focusers using a cross-resonator array with spatially varied geometric parameters atop a continuous gold ground plane spaced by a layer of SiO2. The sub-wavelength cross-shaped building element offers polarization-independent performance and full 2π phase tuning range by varying its width and length, which is explained by an analytical model based on harmonically oscillating dipole antenna. With a radial phase gradient, a metasurface is demonstrated to function as a parabolic reflector at 1.47 μm wavelength with the measured efficiency of 44%. In addition, by elaborately engineering the planar distribution of different building elements, another two focusing reflectors are designed and experimentally verified to anomalously reflect and concentrate light along normal direction but with oblique incident angles of 30° and 60°, respectively.

This letter presents an infrared (IR) focal plane array (FPA) with metamaterial absorber (MMA) integrated to enhance its performance. A glass substrate, on which arrays of bimaterial cantilevers are fabricated as the thermal-sensitive pixels by a polyimide surface sacrificial process, is employed to allow the optical readout from the back side of the substrate. Whereas the IR wave radiates onto the FPA from the front side, which consequently avoids the energy loss caused by the silicon substrate compared with the previous works. This structure also facilitates the integration of MMA by introducing a layer of periodic square resonators atop the SiNx structural layer to form a metal/dielectric/metal stack with the gold mirror functioning as the ground plane. A comparative experiment was carried out on the FPAs that use MMA and ordinary SiNx as the absorbers, respectively. The performance improvement was verified by the evaluation of the absorbers as well as the imaging results of both FPAs.

Most research focuses on varying the resonator and dielectric spacer to configure the absorption and resonant frequency of terahertz (THz) metamaterial absorbers (MAs), where a metal ground plane is used as a perfect reflector of incident THz waves. In this paper, we modulate the MAs absorption by varying the conductivity of the ground plane. Two THz MAs were fabricated by replacing the gold ground planes with cobalt silicide films, and the measured absorptivity decreases by 4% for the electric resonance and increases by 44% for the dipole resonance. Our quantitative analysis reveals that when the conductivity of the ground plane decreases from 1.8 × 107 S/m to 3.0 × 105 S/m, the absorptivity of the electric resonance decreases by 23%, while that of the dipole resonance increases by 62%. Our approach also provides a practical method to measure the electric conductivity of conductive films in the THz regime.

We report the characteristics of a simple complementary metal-oxide-semiconductor compatible terahertz detector device with low response time (nanoseconds) determined using a short-pulse, high intensity free-electron laser. The noise equivalent power was 1 × 10−11 W Hz−1/2. The detector has an enhanced response over narrow bands, most notably at 9.5 THz, with a continuum response at higher frequencies. Using such a device, the dynamics of donors in silicon can be explored, a system which has great potential for quantum information processing.

The authors report on a novel substrate-free cantilever-based focal plane array (FPA) fabricated by a deep reactive ion etching technique and discuss its performance as an uncooled infrared imager. A visible optical readout was designed to simultaneously measure the deflections of all the cantilevers in the FPA. The noise equivalent temperature difference (NETD) of our FPA can be reduced by 60% compared to the one fabricated by sacrificial layer technique and some cantilevers exhibited NETD of 375mK, approaching the theoretical prediction of 89.7mK. The FPA has a bending response to temperature of 86nm∕K and a response time of 21ms.