Abstract
Josephson tunnel junctions have recently proved to be fairly sensitive photodetectors over a broad range of wavelengths. This paper shows the results obtained with Nb/Al-AlOx/Nb Josephson junctions at 4.2 K irradiated via an optical fibre and laser light at λ = 633 nm and 690 nm. The responsivity of the devices is about 50 V/W and is linear over several decades. Moreover, stacks of two Josephson junctions are shown to have twice the responsivity of a single junction. A thermal model of the device is considered and the responsivity is calculated as a function of the temperature derivative of the energy gap, the thermal parameters of the junction, and the modulation frequency of the incident beam.
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