Development of 1.5 THz Photon Detectors for Terahertz Intensity Interferometry

We propose Terahertz Intensity Interferometry (TII) to realize high angular resolution observations above 1 THz. TII uses fast detectors and readout circuits to measure intensity correlation and determine the delay time for synthesis imaging. The development of a fast photon detector at 1.5 THz is discussed for Antarctic TII experiments. The 1.5 THz photon detector is designed to detect terahertz photons with antenna-coupled SIS junctions by pair-breaking process. The detector uses small size and low leakage Nb/Al-AlOx/Al/Nb junctions for high sensitivity at high frequency. The first fabricated detectors show reasonable I-V characteristics at 4 K, and further tuning of fabrication parameters is ongoing. For evaluation of the detectors at 0.8 K using fast cryogenic readout electronics, a new cryostat for the TII experiment will be used. As an initial step, a GaAs-JFET first-stage source-follower is installed at 0.8 K to measure the I-V characteristics of a submillimeter-wave SIS photon detector. The performance shows the new cryostat and the first-stage source-follower at 0.8 K can be used to evaluate 1.5 THz photon detectors, which will be combined with fast readout electronics for TII experiments.