Far-Infrared Vacuum Grating Spectrometer*

A far-infrared grating spectrometer has been developed specifically to investigate gases and solids in the 200–1000μ region. The monochromator is a ƒ/2 Czerny–Turner system and three gratings with constants of 250, 500, and 1000μ are employed. Filtering of unwanted radiation is accomplished by using metallic-mesh reflection filters and a conical light pipe is used for the concentration of the light onto a Golay detector window. This instrument is calibrated by using the pure rotation spectrum of water vapor or methylchloride (CH3Cl).