We present a system capable of broad band frequency domain spectroscopy in the range 6-20 000 cm -1 at cryogenic temperatures. The apparatus couples two different interferometers to a 9 Tesla superconducting split coil magnet and is designed to work with various detectors, including thermal bolometers and semiconducting detectors. The optical layout utilizes an intermediate focus while preserving optical f/#'s throughout enabling DC magnetic field measurements of small crystals with polarized light in both Voight and Faraday geometries. A reference channel eliminates errors associated with system drift and facilitates determination of the optical constants. For transparent samples, simultaneous reflection and transmission can be performed. ©2004 American Institute of Physics.