Abstract
A frequency-multiplication chain to the 3.39 µ m CH4-stabilized He–Ne laser has been constructed using the Josephson point contact as a harmonic mixer. The Josephson harmonic mixer simplifies the chain because it can directly connect the 90 GHz microwave and the 4.25 THz far-infrared frequencies. Tracking oscillators, which track the beat notes by phase locking and regenerate clean signals, also have been developed to correctly count the beat frequencies. The frequency fluctuations of free-running lasers are canceled by counting the beat frequencies with coincident gate timing. The absolute frequency measurement of the He–Ne laser is reported with a standard deviation of about 5 kHz (τ=8 s).
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