An Infrared Vacuum Grating-Prism Spectrometer

A vacuum echelle spectrometer for the near and medium infrared is described together with its prism-order selecting and detector optical systems. The high-dispersion part of the optical system uses a 10.5 cm × 20.2 cm 30-line/mm echelle in a 2.5-m Littrow optical system having 7.5-cm long slits. The limit of resolution at 15 μ using a thermocouple detector is 0.08 cm−1, at 2.5 μ using a cooled PbS cell 0.03 cm−1 can be resolved. Wavelengths can be measured with an accuracy of several thousandths of a wavenumber.