Interferometric Measurement of Wavelengths of Infrared Atomic Emission Lines in the Extraphotographic Region

A considerable extension of the international system of wavelength standards has been achieved by direct interferometric intercomparison of accepted standards with selected infrared lines in the region beyond the limit of photographic response. A radiometric system employed successfully for this purpose scans the pattern of Fabry–Perot fringes projected upon the slit of a spectrometer. By tilting the interferometer in uniform angular motion about a vertical axis, a diametral section of the fringe system moves across the slit, generating a set of maxima that are registered on a uniformly moving record chart with the same distribution as that of the fringe diameters. Items discussed include achromatic projection, vacuum techniques, and procedures for the reduction of data.