A lamellar grating interferometer for the far-infrared

A lamellar grating interferometer has been constructed for use in studies of the optical properties of solids in the frequency range 2-50 cm ^-1. The interferometer uses a 19 × 24cm lamellar grating with a 2.5 cm grating constant and 2.75 cm of travel giving a maximum unapodized resolution of 0.1 cm ^-1. Two 50cm focal length f/1.8 collimating mirrors are used in a Czerny-Turner arrangement. Light-pipe optics feed the light to and from the focal points of the collimating mirrors. The entire assembly is mounted in a vacuum tank which is supported on nitrogen filled bellows for vibration isolation purposes.