An instrument is described that makes convenient the use of high resolution in infrared spectroscopy. While the actual resolution is energy limited, the use of mosaics of gratings up to inches in area makes it possible to resolve close to the theoretical for the largest gratings obtainable. The spectra are recorded directly as graphs of transmittance vs wavelength on scales that are accurate enough to eliminate the need for point by point recalculation. An internal mercury arc gives absolute checks on the accuracy of the sine bar mechanism that generates the wavelength scale. The transmittance scale is based on the optical null double beam principle described by N. Wright and L. W. Herscher [ J. Opt. Soc. Am. 37, 211 ( 1947)] with the added freedom from scattered light that results from a double monochromator.
The spectrometer may be adapted to a wide range of problems by changing detectors, sources, gratings, prisms, and windows. It is usable from the near ultraviolet to as far into the infrared as available prism materials and gratings permit. The grating may be used in any order with either single or double pass of the grating monochromator. The slit and prism drive mechanism may be automatically and continuously synchronized with any of these orders and with any of the different interchangeable components.
The range of operating conditions is very large. The instrument may be operated as a double beam null indicator or as a single beam energy recording instrument. Its scanning time may be adjusted from about 10 minutes to 3 months for the full range of grating angles. Response time may be varied from one second to 100 seconds full scale. The slits may be varied automatically according to any preselected program.
© 1957 Optical Society of AmericaFull Article | PDF Article
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