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A unique optical design consisting of a compound parabolic concentrator and an elliptical concentrator joined at their throats is discussed. The optic has a number of advantages over conventional infrared telescopes for applications in interferometry and photometry. Ray-tracing results are presented.

New theoretical results for noise in cryogenic bolometers are derived. Johnson noise is reduced by as much as 60% by electrothermal feedback from the bias supply. Phonon noise in the thermal link is reduced by as much as 30% relative to the usual equilibrium formula. Photon noise in the Rayleigh-Jeans limit is computed with attention to the attenuation of the photon correlations in the light beam. Basic results on bolometer responsivity, time constant, and thermal properties are presented in a new and convenient form. Excess 1/f and contact shot noise are also discussed.