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Minimum object temperature and data quality in low temperature optical pyrometry depend crucially on the choice and temperature of the detector, on the efficiency of light collection, and on the lay-out of the pre-amplifier. The wavelength range from 1.5 to 5 microns was studied. For the present application (laser flash furnace for use in a shielded hot cell) liquid nitrogen is not available for cooling. The optics must be designed in such a way, that on the one hand as much light as possible is guided from the object onto the detector, whereas on the other hand the image is so well defined that the detector itself limits the object field. For operation at 5 microns these goals are attainable with simple meniscus lenses of Ge or ZnSe, for 1.5 to 2 microns with glass aspheric lenses or even standard achromats. The detectors tested comprise photoconductive PbSe elements and photovoltaic MCT diodes (for 5 microns), as well as photovoltaic Ge or InGaAs diodes (for 1.5 to 2 microns) and Si photodiodes (below 1.05 microns). Amplifier noise depends crucially on the parallel impedance of the detector. The amplifier must be designed in accordance with the type of detector used. Measurement at 5 microns appears to be justified only below 200 C, and requires high aperture optics and/or additional noise reduction through averaging if detector cooling is limited to thermo-electrically attainable -30 C. The best performance in the temperature range 200 to 500 C is obtained with InGaAs detectors. Cooling InGaAs to -30 C only results in a modest improvement in the range 200 to 350 C.

Additional information

Authors: TASMAN H A, JRC Karlsruhe (DE)
Bibliographic Reference: Paper presented: 12th European Conference on Thermophysical Properties, Wien (AT), Sept. 24-28, 1990
Availability: Available from (1) as Paper EN 35549 ORA
Record Number: 199011599 / Last updated on: 1994-12-02
Original language: en
Available languages: en