Optical performance of an ultra-sensitive horn-coupled transition-edge-sensor bolometer with hemispherical backshort in the far infrared
M. D. Audley (SRON–Netherlands Institute for Space Research)
Gert De Lange (SRON–Netherlands Institute for Space Research)
J.R. Gao (TU Delft - QN/Gao Lab, SRON–Netherlands Institute for Space Research)
P. Khosropanah (SRON–Netherlands Institute for Space Research)
R. A. Hijmering (SRON–Netherlands Institute for Space Research)
Marcel Ridder (SRON–Netherlands Institute for Space Research)
Philip D. Mauskopf (Cardiff University)
Dmitry Morozov (Cardiff University)
Neil A. Trappe (Maynooth University)
Stephen Doherty (Maynooth University)
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Abstract
The next generation of far infrared space observatories will require extremely sensitive detectors that can be realized only by combining extremely low intrinsic noise with high optical efficiency. We have measured the broad-band optical response of ultra-sensitive transtion edge sensor (TES) bolometers (NEP ≈ 2 aW / Hz) in the 30-60-μm band where radiation is coupled to the detectors with a few-moded conical feedhorn and a hemispherical backshort. We show that these detectors have an optical efficiency of 60% (the ratio of the power detected by the TES bolometer to the total power propagating through the feedhorn). We find that the measured optical efficiency can be understood in terms of the modes propagating through the feedhorn with the aid of a spatial mode-filtering technique.