NON DISPERSIVE
INSTRUMENTATION
like a dispersion spectrometer, which will yield poor but still usable spectra if the instrument is misadjusted or mis treated, a misaligned Fourier Trans form spectrometer yields nothing. How ever, the available commercial instru ments appear to be quite stable and trouble from this source does not ap pear to be at all serious. The per formance of the Fourier Transform spectrometer is also more dependent on the quality and performance of the electronic components than is the con ventional spectrometer. Instrumentation
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FLUORESCENCE SPECTROMETERS
A rather large variety of spectrome ter systems have been devised, mostly based on the Michelson interferometer. They differ little in principle, but vary greatly as far as the optical, mechani cal, and electronic components are con cerned. The spectral ranges covered depend on the nature of the beam splitter and detector (and, of course, on the associated electronics). Com mercially available instruments now cover the range from 40,000 cm - 1 to 10 cm- 1 (0.25 to 1000 microns). Scan times vary from about l/10th second to several hours. Some instruments in corporate a small computer which is used for recording the interferogram and performing the necessary data re duction; others have a time-averaging computer used for multiple-scanning in order to enhance the signal-to-noise ratio when very weak sources are ob served; still others are equipped with an analog data conversion device. All are quite sensitive. Applications
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ANALYTICAL CHEMISTRY
There is little point in using a Fou rier Transform spectrometer to make a measurement which can be handled quite well with a conventional spec trometer. Using a Fourier Transform spectrometer must be worthwhile. Con sequently, much of the literature describing applications of Fourier Transform spectrometers deals with measurements which are either very difficult or impossible to make with conventional dispersion instruments. Generally, energy-limited situations have been involved, so far—i.e., where the amount of radiation emitted by the source or transmitted, reflected, or emitted by the sample is very small. Fourier Transform spectrometers have consequently performed very well in the far infrared. They have also been very useful in astronomy for recording
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