Fabrication of a Terahertz Imaging System

摘要

During this project, the work on the development of a Terahertz imaging system was performed in the labs of both Prof. Kolodzey and Prof. Goossen. The terahertz and optical components for generating, detecting and manipulating the terahertz beams were designed, developed, and purchased. To evaluate suitable materials for lenses and components, spectra were measured by the technique of Fourier transform infrared spectrometry, using a Thermo- Nicolet 780 system. This FTIR system operates over a frequency range from 0.6 THz to 300 THz (20 to 10,000 cm-1). Spectral transmission measurements for lens materials such as ZnSe, and for architectural materials such as dry-wall (Sheet Rock) were obtained. The development and characterization of a prototype imaging system using a CO2 gas laser source at 28.3 THz (10.6 m wavelength), and a pyroelectric multipixel video camera with a broad spectral response in the THz region was demonstrated. An optical system to expand and collimate the beam using ZnSe lenses was designed and assembled on an optical bench. All of these components were operated at room temperature. This optical delivery system enabled the measurements of the transmission and reflection of objects placed in the terahertz beam path. The arrangement of this terahertz imaging systems was modular in the sense that alternative sources and detectors can be substituted for comparisons of performance, and for operation in difference spectral regimes. Penetration, or see-through, images of a series of objects and materials, including circuit boards, carbon nanotubes, printing ink, DNA, clothing textiles, and animal bone were made and analyzed. We found that the lower terahertz frequencies (0.6 to 3 THz) offer a greater degree of penetration through architectural and textile materials; whereas the upper terahertz frequencies (2 to 10 THz) offer spectral selectivity by having specific spectral lines.