Composite superconducting transition edge bolometer

A composite far-infrared bolometer has been constructed that uses an aluminum film at the superconducting transition temperature of 1.3 K as the temperature-sensitive element. The film is evaporated on one edge of a 4×4-mm sapphire substrate, which is coated on the reverse side with an absorbing film of bismuth. The best bolometer has an electrical NEP of (1.7±0.1) ×10−15 W Hz−1/2 at 2 Hz, and a specific detectivity D* of (1.1±0.1) ×1014 cm W−1 Hz1/2. This measured electrical NEP is within a factor 2 of the fundamental thermal noise limit.