Harmonic mixing and frequency measurement at 2.5 THz using Josephson junctions

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Abstract
The frequency of quartz-crystal oscillators, operating near 120 MHz, has been multiplied by a factor of 21060 and mixed with the frequency of a discharge-pumped water vapour laser operating at 2.53 THz (118 mu m wavelength). The final stage of multiplication and harmonic mixing was performed using point-contact Josephson junctions, with harmonic numbers up to 156. The signal-to-noise ratio of the final intermediate frequency signal was limited by phase noise in the quartz-crystal oscillator, but was about 17 dB higher than that obtained when a klystron, phase-locked to the crystal oscillator, was used as a transfer oscillator. The power levels of the intermediate frequency signals from the Josephson mixer are discussed. The frequency of the laser when set to its Lamp dip was found to be 2527952.91+or-0.05 MHz.