Subterahertz spectroscopy at He-3 temperatures

We report on the design and implementation of an instrument for spectroscopic studies of materials at sub-terahertz (THz) frequencies at temperatures down to 340 mK. We achieved consistent operation under these rather extreme conditions by coupling a modified Martin-Puplett interferometer to a single cryogenic unit housing two independently controlled He-3 platforms: one as a sample stage and the other for bolometric detectors. Both the optical scheme of the interferometer and detector layout are tailored for the use of the two-channel data acquisition mode which is especially advantageous for measurement of absolute values of reflectance as well as for high-resolution spectroscopy. We document the reliable performance of the sub-THz apparatus with several experiments exploring electrodynamics of both conventional and high-T(c) superconductors. (C) 2003 American Institute of Physics.