Performance of NbN lattice-cooled hot-electron bolometric mixers

Abstract
The heterodyne performance of lattice-cooled hot-electron bolometric mixers is measured at 200 GHz. Superconducting thin-film niobium nitride strips with ∼5 nm thickness are used as waveguide mixer elements. A double-sideband receiver noise temperature of 750 K at 244 GHz is measured at an intermediate frequency centered at 1.5 GHz with 500 MHz bandwidth and with 4.2 K device temperature. The instantaneous bandwidth for this mixer is 1.6 GHz. The local oscillator power required by the mixer is about 0.5 μW. The mixer is linear to within 1 dB up to an input power level 6 dB below the local oscillator power. A receiver incorporating a hot-electron bolometric mixer was used to detect molecular line emission in a laboratory gascell. This experiment unambiguously confirms that the receiver noise temperature determined from Y-factor measurements reflects the true heterodyne sensitivity.

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