Experiments using a superconducting point-contact harmonic mixer near 1 THz

Abstract

Experiments are described in which simple and relatively reliable point-contact Josephson junctions were used to generate and mix harmonics (up to the 50th) of microwave klystron frequencies with emissions from a hydrogen cyanide laser operating at 891 GHz. Data are presented illustrating the variation of the intermediate frequency signal with DC bias current through the junction and incident radiation power levels, and the results compared, where possible, with a simple qualitative theory of Josephson mixing. Details are also given of experiments in which such a mixer was used to phase-lock a klystron to the laser, enabling the laser frequency to be accurately and continuously monitored.

Design of a stable CW HCN laser for far infrared frequency synthesis

“…A better current stability would require a much more sophisticated current power supply. The power levels and frequency stability which have been measured are in good agreement with the performances obtained at NBS [1] and NPL [21] for a free running HCN laser.…”

Direct 825th harmonic mixing of a 1 GHz source with an HCN laser in a Josephson junction

“…The maximum IF levels agree fairly well with those predicted on the basis of the mixing model discussed previously (Blaney and Knight 1973). In this model, the maximum peak-to-peak voltage of the IF signal is limited by the spacing of the Josephson constantvoltage 'steps' corresponding to the frequency being multiplied in the junction.…”

“…The experiment could probably be performed with pre-set junctions (Blaney 1971, Blaney andKnight 1973), although more laser power would probably be needed. The required junction characteristics for good performance were much the same as discussed elsewhere (Blaney and Knight 1973, Blaney 1974, Blaney and Knight 1974 although lower resistance junctions (2-10 0) were slightly more favoured. Direct current junction bias was usually employed, although this was not always essential.…”

Frequency measurement at 4.25 THz (70.5μm) using a Josephson harmonic mixer and phase-lock techniques

“…The features of 'high quality' point-contact voltage-current characteristics discussed previously (e.g. Blaney and Knight 1973, Blaney et al 1976b, Weitz et al 1978 were desirable. The observation of a clear Josephson constant-voltage step (at 5-2 mV) when illuminated with 2.52 THz radiation was usually a prerequisite, as were clear steps extending to beyond 6 mV when microwave radiation was applied.…”

“…Full width at half maximum power. Knight 1973). This was probably because the width arising froin phase noise of the spectrum of the klystron harmonic increases proportionately to the frequency, and thus exceeded the loop bandwidth of the synchronisers in this higher frequency case.…”