Fibonacci terahertz imaging by silicon diffractive optics.

Fibonacci or bifocal terahertz (THz) imaging is demonstrated experimentally employing a silicon diffractive zone plate in continuous wave mode. Images simultaneously recorded in two different planes are exhibited at 0.6 THz frequency with the spatial resolution of wavelength. Multifocus imaging operation of the Fibonacci lens is compared with a performance of the conventional silicon phase zone plate. Spatial profiles and focal depth features are discussed varying the frequency from 0.3 to 0.6 THz. Good agreement between experimental results and simulation data is revealed.

Terahertz multilevel phase Fresnel lenses fabricated by laser patterning of silicon.

Multilevel phase Fresnel lenses (MPFLs) with a high numerical aperture for 0.58 THz frequencies were developed. The components based on a monocrystalline silicon wafer are prepared by patterning by a high-speed industrial-scale laser direct writing (LDW) system. Two consistent series of the terahertz-MPFLs with phase quantization levels varying between 2 and the continuous kinoform shape for the focal lengths of 5 and 10 mm were produced employing inherent flexibility of the LDW fabrication process. The focusing performance was studied at the optimal 0.58 THz frequency using a Gaussian beam profile and scanning 2D intensity distribution with a terahertz detector along the optical axis. The efficiency of the terahertz-MPFL was found to be dependent of the number of subzones. The position and orientation angles of the patterned plane of the silicon wafer were considered to reduce the effect of standing waves formation in the experiment.

Antenna-coupled field-effect transistors for multi-spectral terahertz imaging up to 4.25 THz.

We demonstrate for the first time the applicability of antenna-coupled field-effect transistors for the detection of terahertz radiation (TeraFETs) for multi-spectral imaging from 0.76 to 4.25 THz. TeraFETs were fabricated in a commercial 90-nm CMOS process and noise-equivalent powers of 59, 20, 63, 85 and 110 pW/√(Hz) at 0.216, 0.59, 2,52, 3.11 and 4.25 THz, respectively, have been achieved. A set of TeraFETs has been applied in raster-scan transmission and reflection imaging of pellets of sucrose and tartaric acid simulating common plastic explosives. Transmittance values are in good agreement with Fourier-transform infrared spectroscopy data. The spatial distribution of the components in the samples has been determined from the transmission data using principal component analysis.