Frequency selective surface (FSS) radomes can effectively improve the stealth of flying weapons. In this work, an integrated free-standing thick-screen FSS radome is designed using the CST simulation software. The bandpass characteristic is achieved by Y-shape apertures with periodic distribution around the central axis of the radome. Based on a model of a round-head FSS radome with a built-in phased array antenna, we have analyzed the bandpass transmittance and boresight error (BSE) of the radome. The copper shell was prepared by a spin forming process. The FSS radome was fabricated by a laser robot system with multi-degree-of-freedom and a rotary platform. The results of the microwave anechoic chamber test show that the thick-screen bandpass FSS radome has a good electromagnetic performance with a passband transmittance of about 80% and a stopband transmittance of less than 10%.

We report on the fabrication and transmission properties of free-standing single-layer and double-layer THz bandpass filters. These filters are fabricated on aluminum foils using femtosecond laser micro-machining. The aluminum foils are periodically patterned with cross apertures with a total area of 1.75×1.75 cm², also known as frequency-selective surfaces. Their terahertz transmission properties were simulated using the FDTD method and measured using a time-domain terahertz spectroscopy system. The simulation results agree with the measurements results very well. The performance of single-layer bandpass filters is as good as the commercial equivalents on the market. The double-layer filters show extraordinary transmission peaks with changing spacing between the two layers. We show the contour map of the electric field distribution across the apertures, and ascribe the new transmission peaks to the interference and coupling of surface plasmon polaritons between the two layers.

We have observed cyclotron resonance in a high-mobility $\mathrm{Ga}\mathrm{As}∕\mathrm{Al}\mathrm{Ga}\mathrm{As}$ two-dimensional electron gas by using the techniques of terahertz time-domain spectroscopy combined with magnetic fields. From this, we calculate the real and imaginary parts of the diagonal elements of the magnetoconductivity tensor, which in turn allows us to extract the concentration, effective mass, and scattering time of the electrons in the sample. We demonstrate the utility of ultrafast terahertz spectroscopy, which can recover the true linewidth of cyclotron resonance in a high-mobility $(>{10}^6{\mathrm{cm}}^2{\mathrm{V}}^{-1}{\mathrm{s}}^{-1})$ sample without being affected by the saturation effect.

A terahertz metamaterial refractive index/thickness sensor with flexible substrate, exhibiting low-frequency Fano resonance and high-frequency electromagnetically induced transparent (EIT) resonance, is proposed. The physical formation mechanisms of Fano and EIT resonances are investigated by calculating the electromagnetic field. Simulated results demonstrate that the refractive index sensing sensitivity based these two resonances are up to 60 and 100 GHz/RIU, and the thickness sensing sensitivity are up to 1 and 1.7 GHz/μm, respectively. Furthermore, the proposed sensor was fabricated using femtosecond laser etching technology, and its sensing performance was verified by the experimental results that it can distinguish different liquids and detect the polyimide film with different thicknesses less than 180 μm. The remarkable performances make the proposed metamaterial sensor has feasible capability for biological and chemical sensing in terahertz range.

Reverse design is a frontier direction in the optical research field. In this work, reverse design is applied to the design of terahertz devices. We have employed direct binary search (DBS) and binary particle swarm optimization (BPSO) algorithms to design pixel-type terahertz band-pass filters, respectively. Through a comparative analysis of the designed devices, we found that BPSO algorithm converged faster than DBS algorithm, and the device performance is better on out-of-band suppression. We have fabricated a sample utilizing femtosecond laser micromachining and characterized it by terahertz time-domain spectroscopy. The experimental results were consistent with the finite difference time domain (FDTD) simulation. Our method can simultaneously optimize multiple characteristics of the band-pass filters, including the peak transmittance, out-of-band transmittance, bandwidth, and polarization stability, which can not be achieved by traditional optical design methods.