A Double-Pass Spectrometer*

Abstract

An optical system for obtaining doubly passed grating and prism spectra is described and its application to infrared spectroscopy is discussed. The optical system consists of a spherical field mirror which is placed in the focal plane of the spectrometer and a spherical reimaging mirror which receives radiant energy from the field mirror. Features of the new system are ease of adjustment and freedom from vignetting. The system has been set up and tested both in a high-resolution grating spectrometer and in a low-resolution order-sorting prism instrument.