Terahertz Imaging With 3D-Printed Risley-Prism and Telecentric Objective

Nondestructive evaluation is one of the key envisaged applications for terahertz technology due to nonionizing 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, 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 Risley-prism 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.