Terahertz Imaging With 3D-Printed Risley-Prism and Telecentric Objective
Bryce Chung, Daniel Headland, Withawat Withayachumnankul
Abstract
Non-destructive evaluation is one of the key envisaged applications for terahertz technology due to non-ionizing energy levels and the ability to penetrate many optically opaque materials. Conventional terahertz imaging systems typically rely on raster scanning the target with a moving transceiver, or make use of goniometric beam manipulation schemes. As an alternative, we propose the use of a Risley-prism, essentially a cascaded pair of independently rotating prisms, to function as a simple beam-steering mechanism. When deployed in conjunction with an aspheric, telecentric objective, the Risley-prism allows for scanning a focused terahertz beam in two dimensions. We utilize 3D-printed cyclic olefin copolymer (COC), a low-loss and low-dispersion polymer, to minimize material loss and facilitate the construction of these bulk optics. Owing to true time delay, our imaging system operates over 220-330 GHz, making use of this bandwidth for resolving depth features and hidden objects. We achieve a spatial resolution of 0.419 lp/mm over a circular scanning region 27.8 mm in diameter. The proposed Risleyprism imaging system offers a simple solution to the complicated problem of broadband and high resolution imaging, and hence is readily amenable to widespread adoption and commercial applications.