Some Factors Affecting the Sensitivity and Spectral Response of Thermoelectric (Radiometric) Detectors

Abstract

A number of thermal detectors (thermopiles) has been studied for variations in sensitivity which exist over their surfaces and also for variations of sensitivity with wavelength. These variations differ depending upon whether the thermoelectric output is measured with dc instrumentation, with conventional ac instrumentation, or with ac synchronous rectifier instrumentation. In general, lower responses for the longer wavelengths are observed when commercial thermopiles are compared with a new cavity black-body detector—and the difference may be greater when measured with ac synchronous rectifier instrumentation. When the output of a detector is measured through the use of a conventional tuned ac amplifier, variation in sensitivity of as much as 5 to 1 has been found for different areas of the surface. When a phase-sensitive amplifier is employed, first set for maximum response with the entire thermopile irradiated, even larger variations in sensitivity may be observed.