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The principle of a terahertz detector using a superconducting tunnel junction (STJ) coupled to a large terahertz-absorbing superconductor film is verified. We have detected terahertz radiation based on the Cooper-pair breaking process, and confirmed that the sensitivity has a sharp increase around 0.7 THz, a value that is in agreement with the gap frequency of the superconducting Nb. For high-sensitivity terahertz detection, we propose an improved design of the STJ detector composed of a smaller junction coupled to a thinner superconductor film. We also discuss the expected noise equivalent power of the optimized detector.

We demonstrated terahertz imaging using a direct detector based on niobium superconducting tunnel junctions (STJs). The detector is composed of linearly distributed junctions placed on a superconducting microstrip line and is integrated on two wings of a log-periodic antenna. We succeeded nondestructive imaging for an integrated-circuit card and dry material using the detector around its sensitivity peak (∼0.66THz). The dynamic range was measured to be higher than 4×107 (76dB). Thus, the STJ detector is applicable to high-sensitivity and high-speed terahertz imaging for various nondestructive inspection applications.