We measure the direct detection effect in a small volume (0.15μm×1μm×3.5nm) quasioptical NbN phonon cooled hot electron bolometer mixer at 1.6THz⁠. We find that the small signal sensitivity of the receiver is underestimated by 35% due to the direct detection effect and that the optimal operating point is shifted to higher bias voltages when using calibration loads of 300K and 77K⁠. Using a 200GHz bandpass filter at 4.2K the direct detection effect virtually disappears. This has important implications for the calibration procedure of these receivers in real telescope systems.

Topics
Phonons, Superconductivity, Superfluids, Linear filters, Antennas, Signal processing, Observational astronomy, Telescopes, Electromagnetic radiation detectors, Lenses
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© 2005 American Institute of Physics.
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