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The Adaptation of a Commercial Double-Beam Infrared Spectrophotometer for use with a Grating

Volume 11, Number 1 (Feb. 1957) Page 31-38

Mattraw, H.C.; Landis, F.P.

A 60 line/mm Bausch and Lomb grating has been installed in a Baird Infrared Spectrophotometer in place of all prisms to cover the 2 to 26 micron range of the instrument. No changes were made in the optical system for the 2 to 10 micron region. To avoid overlapping of higher orders on the longer wave length first order spectrum, one small mirror was replaced by a crystal of MgO An alternate method, referred to as negative filtering, is presented for the elimination of overlapping orders and may be used with the double-beam instruments. The existing scanning equipment was used with the following modifications. (1), a mechanical linkage was tied to the existing Littrow mirror drive to rotate the grating and (2), new cams were substituted for the prism cams to provide linear wave length scans with the grating. One cam covers 6 microns of any region of the spectrum before resetting the grating, while the second cam can be used to obtain four times the dispersion of the first cam.

The method described is simple to install and has the flexibility to obtain spectra with up to ten times the dispersion of the NaCl or KBr prisms.