A Broad Range Vacuum Spectrograph for the Extreme Ultraviolet

Abstract

A two meter focus, normal incidence, vacuum spectrograph is described which covers on one plate the whole range from the zero order up to the first order of λ2500. The 30,000 line per inch glass grating gives a dispersion of about 4.27A per mm and strong spectra are obtained to as short wave‐lengths as λ300, with lines a little below λ200 showing on long exposures. The body of the spectrograph is exhausted by an Aristovac pump to a pressure of 2×10⁻⁵ mm, a vacuum guard ring device of double rubber gaskets being used to seal the end covers. The instrument is particularly suitable for the establishment of short wave‐length standards and for the study of line and band spectra from gas discharges and the study of absorption spectra in gases. The limitations of the instrument are discussed and suggestions are given, based on several years' experience with this instrument, for a spectrograph of new design which would avoid most of the difficulties inherent in this general type of vacuum spectrograph.