Study on Optical Filter Heating in Background Limited Detector Experiments
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Cryogenic test setups with controlled stray light environments capable of reaching ultra-low radiative background levels are required to test far infrared (FIR) and submillimeter (sub-mm) wave radiation detectors for future space based observatories. In recent experiments (Nature Commun 5:3130, 2014), in which 1.54 THz radiation was coupled onto an antenna-coupled kinetic inductance detector (KID), we found a higher than expected optical loading. We show that this can be explained by assuming heating of the metal mesh IR filters and re-radiation onto the KID. Note that the total power from the cryogenic black body source used in the experiments (at T = \(3\)–\(25\) K) is much larger than the power inside the \(1.5\)–\(1.6\) THz band we use to calibrate our detector. The out-of-band radiation can have up to 5 orders of magnitude more power than inside the \(1.5\)–\(1.6\) THz band of interest. A strategy to mitigate the filter heating problem is presented, and when it is implemented, the validated upper limit for stray light at the detector level is down to few aW.
KeywordsCryogenic setup Ultra low background Optical filters
This work has been supported as part of a collaborative project, SPACEKIDS, funded via grant 313320 provided by the European Commission under Theme SPA.2012.2.2-01 of Framework Programme 7.
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