William L. Calvert

The Design and Performance of a Double-Beam Infrared Spectrophotometer

A double-beam infrared spectrophotometer is described. The features include use of one solid angle of radiation for both beams (alternating at 5.5 cps); interchangeable sodium chloride and potassium bromide prisms and 3600 and 7500 lines per inch gratings; and optional modes of automatic recording, either percent transmission on strip chart or expanded recording of energy differences. Significant is the use of two rotating segmented mirrors with the source being imaged in the plane of the first mirror, then in the plane of the second, and, finally, upon the entrance slit of the spectrometer. Steadiness of the source image upon the slit is, therefore, independent of adjustment and quality of the rotating mirrors.