@article {156296,
	title = {Far-infrared frequency-dependence of the AC Josephson effect in niobium point contacts},
	journal = {Physical Review B},
	volume = {18},
	number = {7},
	year = {1978},
	pages = {3282-3292},
	abstract = {We have measured the far-infrared frequency dependence of the strength of the ac Josephson effect in Nb cat-whisker point contacts, which have consistent and reproducible behavior and minimal extrinsic high-frequency limitations due to capacitance and heating. We monitor the constant-voltage Josephson steps induced on the dc\&nbsp;I-V\&nbsp;curves by an optically pumped far-infrared laser at fundamental frequencies corresponding to voltages from \~{}0.2 to \~{}2 times the energy-gap voltage. At all the frequencies studied, we find that the shape of the power dependence of the step amplitudes is fit reasonably well by Werthamer{\textquoteright}s frequency-dependent theory for tunnel junctions in the voltage-bias approximation. However, the observed magnitude of the steps is considerably less than predicted by the theory. By fitting to the\&nbsp;I-V\&nbsp;curves of the steps, we find that some of this discrepancy can be accounted for by heating-enhanced noise rounding. The remaining discrepancies (of the order of a factor of 2) are attributed to departures from a voltage bias at low frequencies and, tentatively, to the effects of the Ginzburg-Landau relaxation time at higher voltages. Our data confirm the expected intrinsic roll off of the strength of the ac Josephson effect above the energy gap.},
	url = {https://journals.aps.org/prb/abstract/10.1103/PhysRevB.18.3282},
	author = {Weitz, D. A. and Skocpol, W. J. and Tinkham, M.}
}
