A NEW FAR INFRARED SUBMILLIMETER SPECTROMETER UTILIZING INTERFEROMETRIC MODULATION$^{\ast}$

Abstract

A grating spectrometer for the 50-1000 micron region has been built, utilizing the order-sorting filtering properties of the interferometric modulator described in the previous paper. The radiation detected is greater than 90% pure first order throughout the region between 50 and 1000 microns. The instrument is composed of source-, sample-, monochromator-, modulator-, and detectorunits, each contained in a separate vacuum tank. The monochromator is a f/4 Czerny-Turner arrangement using gratings blazed at 100, 200, 400, and 800 microns. A 250 watt mercury lamp is the source, and the radiation is detected by a Golay cell. The entire instrument is evacuable to a pressure of less than 0.05 Torr. The use of an individual unit for each function permits considerable flexibility through the interchange of components. This allows investigation of a wide variety of experiments, including the measurement of transmission and reflection spectra of cooled solids. Examples of data taken with the spectrometer will be shown. These include the ubiquitous $H_{2}O$ vapor spectrum, and the transmission of some crystals in this region.