A far-infrared laser study of Josephson point contacts

The high-frequency behavior of niobium cat-whisker point contacts is studied using radiation from an optically pumped far-infrared (FIR) laser. The FIR molecular laser had a dielectric-waveguide cavity and was pumped by a CO2 laser. The use of capacitive-mesh output couplers is extended throughout the FIR spectrum, between 42 micrometers and 1.2 mm, and have found the optimum grid constants for several lines. At shorter wavelengths, the laser performance was improved by the use of a novel hybrid capacitive-mesh hole output coupler. The coupling of the FIR radiation to the point contact is found to depend in a simple manner on the resistance of the contact. The FIR laser radiation induces constant-voltage steps on the dc I-V curves of the junctions, allowing the high-frequency ac Josephson effect to be studied.