Characterization of Widefield THz Optics Using Phase Shifting Interferometry

• Published in: IEEE transactions on terahertz science and technology 2023-11, Vol.13 (6), p.614-621
• Main Authors: Reyes, Nicolas, Mayorga, Ivan Camara, Grutzeck, Gerrit, Yates, Stephen J.C., Baryshev, Andrey, Baselmans, Jochem, Weiss, Axel, Klein, Bernd
• Format: Article
• Language: English
• Subjects: Astronomical instruments; Continuous radiation; Detectors; Experimental methods; Focal plane; Inductance; Instruments; kinetic inductance detectors; Optical detectors; Optical diffraction; Optical mixing; Optical polarization; Optical reflection; Optics; Parameters; Terahertz frequencies; terahertz optics; Wave fronts
• ISSN: 2156-342X; 2156-3446
• DOI: 10.1109/TTHZ.2023.3320554

Characterization of wide-field optics in the Terahertz regime imposes new and demanding requirements for testing systems. Basic optical parameters can be determined from scalar planar characterization, obtained using monochromatic or thermal sources located in the instrument focal plane. In contrast, important features, such as the spillover efficiency, wave front error, or aperture efficiency cannot be easily measured by such approaches. Moreover, when instruments have a curved focal plane, designed to match the hosting telescope, even basic parameters are difficult to extract from scalar planar measurements. In such cases, the use of phase and amplitude information is mandatory. From a complex planar measurement, the complete information of the optical system can be obtained, allowing the estimation of all relevant optical parameters. In this work, we present and demonstrate experimentally a technique to perform such measurement based on the use of continuous wave photonic terahertz sources. Here, we present our results at 350 GHz and 850 GHz, demonstrating the feasibility of performing measurements at different submillimeter frequencies using a single experimental setup. The proposed system was implemented to fully characterize a wide-field submillimeter camera based on kinetic inductance detectors designed to be deployed at the APEX Telescope in Chile.