A detector (based on the temperature dependence of ferroelectricity in some crystals) which produces an electrical signal proportional to the energy flux on the collector surface.
Source:
Orange Book, 2nd ed., p. 193 (https://media.iupac.org/publications/analytical_compendium/)
See also:
PAC, 1995, 67, 1745. 'Nomenclature, symbols, units and their usage in spectrochemical analysis-XI. Detection of radiation (IUPAC Recommendations 1995)' on page 1752 (https://doi.org/10.1351/pac199567101745)