Echelle-Type Spectrograph for the Near Infrared*

Abstract

The 5-m evacuable double-passed grating spectrograph previously described has been modified so that all but 10 in. of the total optical path is now evacuable.The foreprism system has been redesigned so that overlapping high-order infrared spectra can be separated allowing the use of coarse gratings. Provision is made to keep the band pass of the foreprism monochromator in synchronization with the rotation of the grating.An addition to the scanning system provides wavelength markers on the recorder chart. The wavelength marker system is arranged so that accelerated scanning can be performed in traversing regions where lines are not being measured. The marker system is also useful in expediting the measurement of small frequency shifts.The procedure used for accurate determination of the dispersion by means of interferometric calibration is described.