Chapter 5 - Detectors for Infrared, Optical and X-ray Photons

Abstract

This chapter discusses detectors that use superconducting materials for the detection of infrared, optical and x-ray photons, focusing on signal generation and noise sources of cryogenic detectors such as superconducting tunnel junctions and bolometer/calorimeter. It deals with detectors based on thin-film superconducting sensors for the detection of photons in an energy range from 0.1-10 keV. Bolometer, designed to detect incident power, is a popular instruments in space radiometry, for sub-mm wavelength observations and thermal imaging for military and biomedical applications. The main motivation for the development of calorimeter and superconducting tunnel junctions operating in the mK-temperature region was the lack of efficient high-resolution detectors, especially for x-ray astronomy and material analysis. The aim is to combine the high quantum efficiency of energy dispersive detectors with the very good resolving power of wavelength dispersive detectors. Superconducting tunnel junctions consist of two thin films of superconductors, separated by a thin tunnel barrier through which quantum-mechanical tunneling can occur. These detectors are operated at a temperature well below the transition temperature of the superconductor. The tunnel current through the barrier is proportional to the number of quasi-particles in the superconducting tunnel junction (STJ). The chapter discusses the properties of superconducting tunnel junctions highlighting various parameters related to STJ such as signal and its loss, signal noise, and photon detection. The chapter also focuses on thermal detectors and ends with a discussion on future prospects of superconducting detectors.