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IEEE Transactions on Instrumentation and Measurement

Point-contact-type Josephson harmonic mixer for frequency measurement of far-infrared lasers

Yukinobu Miki, Eiichi Sakuma, Masanao Morimura

Published Jun 1, 1987• 3 citations
Publisher

Abstract

Point-contact-type Josephson junctions have been developed as a harmonic mixer to measure far-infrared (FIR) laser frequencies in a frequency chain up to the infrared region. The junctions were formed by mechanically pressing a niobium wire of 70 μm in diameter with a sharply etched tip against a niobium post of 2 mm in diameter. The voltage-current characteristics of the mixers were investigated under the irradiation of FIR lights from an optically pumped methyl-alcohol laser. The Shapiro steps for FIR lights up to 3.1 THz were observed. The mixing properties of the mixers were studied through harmonic mixing experiments of 50-GHz microwaves and the FIR lights up to the frequency of 3.1 THz. The conversion efficiency of the beat signals to the incident FIR power was found to vary as the — 4th power of the FIR frequency. From the mixing properties, the combination of the critical current Icof the junction and the product IcRnwhere Rnis the normal resistance of the junction, was found important to optimize the mixing performance.

DOI
10.1109/tim.1987.6312756

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Recently there has been a marked upsurge in interest in the construction of multipliers and mixers for the SHF and IR regions. Of special interest in this respect are Josephson junctions fabricated from high-temperature superconductors. The present paper reports the results of experimental investigations of superconducting point junctions (SPJ) fabricated from the high-temperature superconductor Nb3Sn, and operating in regimes of frequency multiplication and mixing in the SHF spectral region. A controllable Nb3Sn Nb3 Sn SPJ that could be adjusted after being immersed in liquid helium was used in the experiments. The method of preparation of the SPJ was the same as the one that was employed in Ref. 1. The assembled experimental setup allowed the SPJ to be irradiated with three-centimeter and four-millimeter microwaves separately and simultaneously. The current-voltage characteristics (CVO) of the (tuned) SPJ were registered on an oscillograph and then recorded automatically at different DHF-power levels. The differential resistance RD = dU/dl of the junction as a function of mixing voltage UO was recorded with the aid of a lock-in amplifier2 co nstructed by us. All the measurements were carried out at the liquid-helium temperature. The SPJ in question had the following parameters: the critical current Ic = 0.1–2.5 rnA and the resistance in the normal state Rn = 0.1–10 Ω. When the SPJ was subjected to 8.9- and 87-GHz radiation separately, the CVC exhibited current steps at voltages corresponding to the fundamental frequency and the harmonics of the external radiation, as well as a sub harmonic structure. The multiplication of the fundamental frequency to 1 THz was recorded in the case of the irradiation of the SPJ by an 8.9–GHz signal and the registration of the dependence of RD on the mixing voltage U0. This differential CVC exhibited a subharmonic structure near the fundamental frequency at low SHF-power levels and near this frequency and its harmonics at higher levels. When the SPJ was irradiated by 87-GHz signals, the multiplication of the fundamental frequency of the signals to 2.2 THz was recorded on the differential CVC. The SHF-power dependence of the harmonics and subharmonics had an oscillatory character. The mechanism underlying the formation of the sub harmonic structure on the CVC of the SPJ can be explained if we take account of the effect of the action of the Josephson self-radiation on the junction itself.3 It should be noted that the manifestation of the Josephson properties in the frequency range ∼1 · 1012 Hz was observed for a SPJ with high Ic and Rn ⩾ 1 Ω. When the Nb3Sn–Nb3Sn SPJ was irradiated by two signals with frequencies 87 and 8.9 GHz simultaneously, there appeared near the steps for the 87-GHz signal , as the power of the 8.9-GHz signal was increased, steps corresponding to signals with frequencies equal to combinations of the two frequencies, i.e., (87m ± 8.9k)-Ghz combination steps appeared on the eve. Thus, the first experimental investigations of the multiplication and mixing of signals by Nb3Sn-Nb3Sn SPJ have shown that such SPJ operate quite well in regimes of mixing and multiplication of external SHF radiation.

Soviet Journal of Low Temperature Physics•Jun 1, 1980•0 citations
Point-contact-type Josephson junctions have been developed as a harmonic mixer to measure far-infrared (FIR) laser frequencies in a frequency chain up to the infrared region. The junctions were formed by mechanically pressing a niobium wire of 70 μm in diameter with a sharply etched tip against a niobium post of 2 mm in diameter. The voltage-current characteristics of the mixers were investigated under the irradiation of FIR lights from an optically pumped methyl-alcohol laser. The Shapiro steps for FIR lights up to 3.1 THz were observed. The mixing properties of the mixers were studied through harmonic mixing experiments of 50-GHz microwaves and the FIR lights up to the frequency of 3.1 THz. The conversion efficiency of the beat signals to the incident FIR power was found to vary as the — 4th power of the FIR frequency. From the mixing properties, the combination of the critical current Icof the junction and the product IcRnwhere Rnis the normal resistance of the junction, was found important to optimize the mixing performance.
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 our junctions, allowing us to study the high-frequency ac Josephson effect.
Thin film niobium nitride Josephson tunnel junctions have been used as harmonic mixers in experiments to measure the frequency of various submillimetre wavelength laser lines. The Josephson junctions were used as harmonic mixers with an 18-40 GHz microwave synthesiser providing the local oscillator signal. Harmonics up to the 140th of ∼18 GHz, generated within the junction, mixed with optically pumped laser lines up to 2.5 THz to produce output signals around 20 MHz. Results of frequency measurements and data on the performance of the mixing system, including signal to noise ratios and frequency response, will be presented.
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.
Recently there has been a marked upsurge in interest in the construction of multipliers and mixers for the SHF and IR regions. Of special interest in this respect are Josephson junctions fabricated from high-temperature superconductors. The present paper reports the results of experimental investigations of superconducting point junctions (SPJ) fabricated from the high-temperature superconductor Nb3Sn, and operating in regimes of frequency multiplication and mixing in the SHF spectral region. A controllable Nb3Sn Nb3 Sn SPJ that could be adjusted after being immersed in liquid helium was used in the experiments. The method of preparation of the SPJ was the same as the one that was employed in Ref. 1. The assembled experimental setup allowed the SPJ to be irradiated with three-centimeter and four-millimeter microwaves separately and simultaneously. The current-voltage characteristics (CVO) of the (tuned) SPJ were registered on an oscillograph and then recorded automatically at different DHF-power levels. The differential resistance RD = dU/dl of the junction as a function of mixing voltage UO was recorded with the aid of a lock-in amplifier2 co nstructed by us. All the measurements were carried out at the liquid-helium temperature. The SPJ in question had the following parameters: the critical current Ic = 0.1–2.5 rnA and the resistance in the normal state Rn = 0.1–10 Ω. When the SPJ was subjected to 8.9- and 87-GHz radiation separately, the CVC exhibited current steps at voltages corresponding to the fundamental frequency and the harmonics of the external radiation, as well as a sub harmonic structure. The multiplication of the fundamental frequency to 1 THz was recorded in the case of the irradiation of the SPJ by an 8.9–GHz signal and the registration of the dependence of RD on the mixing voltage U0. This differential CVC exhibited a subharmonic structure near the fundamental frequency at low SHF-power levels and near this frequency and its harmonics at higher levels. When the SPJ was irradiated by 87-GHz signals, the multiplication of the fundamental frequency of the signals to 2.2 THz was recorded on the differential CVC. The SHF-power dependence of the harmonics and subharmonics had an oscillatory character. The mechanism underlying the formation of the sub harmonic structure on the CVC of the SPJ can be explained if we take account of the effect of the action of the Josephson self-radiation on the junction itself.3 It should be noted that the manifestation of the Josephson properties in the frequency range ∼1 · 1012 Hz was observed for a SPJ with high Ic and Rn ⩾ 1 Ω. When the Nb3Sn–Nb3Sn SPJ was irradiated by two signals with frequencies 87 and 8.9 GHz simultaneously, there appeared near the steps for the 87-GHz signal , as the power of the 8.9-GHz signal was increased, steps corresponding to signals with frequencies equal to combinations of the two frequencies, i.e., (87m ± 8.9k)-Ghz combination steps appeared on the eve. Thus, the first experimental investigations of the multiplication and mixing of signals by Nb3Sn-Nb3Sn SPJ have shown that such SPJ operate quite well in regimes of mixing and multiplication of external SHF radiation.