Noise Bolometer for Terahertz Waves

Abstract

An advantage of superconducting detectors is a much lower noise in comparison to their semiconductor counterparts. We have studied the magnitude and spectrum of electric noise in thin superconducting NbN nanostrips carrying a subcritical current. Analysis of the experimental data suggests that the noise appears due to fluctuations in the two-dimensional vortex gas below the Kosterlitz-Thouless phase transition. Implementing this approach to the noise mechanism, we proposed a novel detector. The novelty is the use of the noise, which generally hampers the performance of conventional detectors, as the physical quantity that itself senses radiation. Our detector patterned from a thin NbN superconducting film and integrated in a planar log-periodic antenna. The detector operates at 4.2 K in the current-carrying superconducting state. Optically measured noise-equivalent power amounted at 10^-13 W / Hz^1/2 and is likely to improve at lower temperatures.