INFRARED RADIATION THERMOMETRY USING A WOLLASTON PRISM BASED COMPACT FOURIER TRANSFORM SPECTROMETER. Franklin J. Dunmore, Optical Technology Division, Optical Material and Infrared Technology Group, Building 220, Room A321, NIST Gaithersburg MD 20899. ( 301-975-2328, e-mail: dunmore@garnet.nist.gov)

Radiometry and radiation thermometry traditionally is done using dispersive spectrometry techniques, which are characteristically time consuming due to the long integration time of a weak signal extracted form a narrow bandwidth within a broad spectrum. This should be contrasted with Fourier transform (FT) spectrometry which gives much faster extraction of the spectra. A further improvement is Wollaston prism based (spatial domain) FT spectrometer, which is quite compact (typically no larger than a 35mm camera), has no moving parts, and allows practical "snapshot" extraction of spectra (integration times down to 1 millisecond). A new spectrometer of this type (built by Photonex LTD) was used to attempt precise radiation thermometry in the wavelength or frequency range of 400 to 1100 nm or 9000 to 25000 1/cm of a high stability, high temperature (up to 2700 K) argon purged graphite blackbody source. Planck's Radiation Law was used to calibrate the spectrometer and analyze the data. Temperatures of the blackbody source were measured by fitting the data to Planck's law. Various temperatures were measured in the range of from 1100 K to 2700 K, within accuracies varying from within 40 K to 3 K of that obtained by to standard pyrometric techniques and with precision of " 1 to " 5 K.

This is not as accurate as dispersive techniques. A likely source of the error is excess gain in some of the pixels of the linear diode detector array. This should be fixed by calibration for anomalous pixels in the spectrometer software. This will give a detector based standard for realization of a radiance temperature scale, and establish traceability between primary and secondary standards laboratories.