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Optical Performance of Photoinductive Mixers at Terahertz Frequencies

Authors:
E.N. Grossman, J.E. Sauvageau, D.G. McDonald
Abstract:
We have investigated the electrical and optical properties of detectors based on the change in kinetic inductance of a superconducting film with incident terahertz-frequency radiation. Two different geometric configurations, stripline and slotline, of these photoinductive detectors have been explored. Both include a loop of thin niobium coupled to the incident radiation through a lithographic antenna; the loop inductance is read out via an integrated D.C. SQUID. The slotline geometry is substantially simpler to fabricate, but electrically, the two geometries have very similar properties. The loop inductance varies with temperature in good agreement with the 2-fluid model, while thee critical current varies with temperature in agreement with Ginzburg-Landau theory. The maximum voltage-flux transfer characteristic of the SQUID varies with temperature according to the empirical relation dV/d[Phi](max) = R/L, where R is the resistance of the junction shunt resistors and L the loop inductance. The thermal conductance is less accurately determined experimentally, but the approximate value of 5e10-7 W/K implies a peak electrical responsivity of 2200 V/W. No excess audio frequency noise has been observed down to our amplifier's noise floor of 190 pV/Hz1/2 . This yields an electrical noise-equivalent-power (NEP) of 8 × 10-14 W/Hz1/2, a factor of 2.5 from the expected phonon-noise limit. The response to 992 GHz laser radiation varies with reduced temperature as expected for a purely bolometric response in the limited range over which it was examined, .78 < t < .95. The optical power level at which the response saturates indicates that in a heterodyne mixing application, the optimum local oscillator power level would be approximately 2 nW.
Categories:
Devices
Year:
1993
Session:
12
Full-text:
Download a PDF of this paper.
Page Number(s):
588-604