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In optical pyrometry at low temperatures, the minimum measurable temperature and quality of results achieved are determined by the choice of detector, by its temperature, by the aperture recorded and by the type of (pre-) amplifier. Tests were carried out in the wavelength range 1.5 to 5 microns. In the application described (laser flash equipment for operation in a hot cell) liquid nitrogen is not suitable. The optical components should conduct as much light as possible to the detector, yet produce such a sharp image that the detector surface can serve as an effective object-side aperture diaphragm. For 5 microns this can be achieved using simple Ge or ZnSe meniscus lenses, for 1.5 to 2 microns with aspherical lenses or even with standard glass achromatics. The following were compared: photoconducting PbSe detectors and photovoltaic MCT diodes (for 5 microns), photovoltaic Ge or InGaAs diodes for (1.5 to 2.6 microns) and Si (less than 1.05 microns). Amplifier noise essentially depends on the parallel impedance of the detector. The amplifier must be adapted to the type of detector. Above 300 C measurement at 5 microns is of little advantage.

Additional information

Authors: TASMAN H A, JRC Karlsruhe (DE)
Bibliographic Reference: Paper presented: Frühjahrstreffen des Arbeitskreises Thermophysik, Stuttgart (DE), May 7-8, 1990
Availability: Available from (1) as Paper DE 35475 ORA
Record Number: 199011250 / Last updated on: 1994-12-01
Original language: de
Available languages: de