Title :
Far-infrared kinetic-inductance detectors
Author :
Grossman, E.N. ; McDonald, D.G. ; Sauvageau, J.E.
Author_Institution :
Nat. Inst. of Stand. & Technol., Boulder, CO, USA
fDate :
3/1/1991 12:00:00 AM
Abstract :
Extremely sensitive far-infrared detectors suitable for both direct detection and heterodyne applications, based on μm-sized thin films with thickness less than a superconducting penetration depth are possible. The penetration depth of such a film, and therefore its inductance, varies with temperature and with quasiparticle population (described by an effective temperature T*), resulting in both bolometric and nonequilibrium photoinductive responses. Incident radiation is coupled into the small-area kinetic inductor by a lithographic antenna, and the resulting inductance changes are amplified and converted to a voltage signal by an integrated microstrip DC SQUID. The device is sensitive because, unlike junction-based devices with large capacitive reactances, the kinetic inductor is naturally well matched to the antenna impedance at the far-IR frequency (ν>2Δ/h) and to the preamplifier (SQUID) impedance at microwave or video frequencies (ν≪2Δ/h). The best kinetic inductor materials are those with low electronic mean free path, large penetration depth, and high critical current density. Thus, common magnet alloys such as NbTi are the natural choice for liquid-He temperature operation. A detailed analysis predicts a (phonon-limited) NEP of 4×10-17 W/√Hz for a bolometer with an iridium kinetic inductor operated at 0.1 K. A heterodyne noise temperature of 2250 K (single-sideband) at 3 THz, with a 200-MHz bandwidth, is predicted for a Nb-Ti mixer operated at 4 K
Keywords :
SQUIDs; infrared detectors; mixers (circuits); 0.1 to 4 K; 200 MHz; 3 THz; NEP; NbTi mixer; bolometric response; critical current density; direct detection; far-IR frequency; heterodyne detection; heterodyne noise temperature; impedance matching; inductance changes; kinetic-inductance detectors; liquid-He temperature operation; lithographic antenna; microstrip DC SQUID; microwave frequencies; photoinductive responses; sensitive far-infrared detectors; small-area kinetic inductor; superconducting penetration depth; video frequencies; voltage signal; Detectors; Impedance; Inductance; Inductors; Kinetic theory; Microstrip antennas; SQUIDs; Superconducting magnets; Superconducting microwave devices; Temperature sensors;
Journal_Title :
Magnetics, IEEE Transactions on