Fibonacci subTerahertz imaging: features and applications

Fibonacci or bifocal terahertz (THz) imaging based on silicon diffractive zone plate in a continuous wave mode at 0.6 THz is demonstrated. Silicon as a low absorbing material was used in the laser ablation process to fabricate the Fibonacci structures. Zone plates were designed by the three-dimensional finite-difference time-domain method. To illustrate the Fibonacci focusing, the performance was studied both theoretically and experimentally by determining spatial profiles, the distance between the foci and the focal depth at frequencies of 0.3 THz and 0.6 THz. Terahertz images of various packaged objects at the 0.6 THz frequency were simultaneously recorded with the spatial resolution of wavelength in two different planes separated by 7 mm distance. Imaging performance using the Fibonacci lens is compared with the operation of the conventional silicon phase zone plate.