Electron temperature fluctuation noise in hot-electron superconducting mixers

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Abstract
An experimental study is presented of the output noise in hot-electron superconducting NbN bolometer mixers. Fluctuations of the electron temperature have been shown to be the main source of electrical noise. The rolloff frequency of the spectral noise density corresponds well to the inverse electron temperature relaxation time (≊230 ps). Equivalent noise data have been obtained for the device at a physical temperature within superconducting transition region, and at a somewhat lower physical temperature with the device pumped by 350 GHz radiation to reach the same operating point. The single sideband (SSB) mixer noise temperature due to intrinsic noise mechanisms for the NbN device is estimated to 360 K independent of radiation frequency. A larger critical current density may promote a further reduction of the intrinsic conversion loss of the mixer device.

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