Low noise submillimeter SIS receiver with niobium nitride quasiparticle tunnel junctions

We have developed and tested a submillimeter waveguide SIS mixer with NbN-MgO-NbN quasiparticle tunnel junctions. The two junction array is integrated in a full NbN printed circuit. The NbN film critical temperature is 15 K and the junction gap voltage is 5 mV. The size of the junctions is 1.4 × 1.4 µm and Josephson critical current density is about 1.5 KA/cm² resulting in junction R_NC product about 40. The inductive tuning circuit in NbN is integrated with each junction in two junction array. A single non contacting backshort was tuned at each frequency in the mixer block.At 306 GHz the minimum DSB receiver noise temperature is as low as 230 K. The sources of the receiver noise and of the limits of the NbN SIS submillimeter mixer improvement are discussed.     

A 650-GHz Band SIS Receiver for Balloon-Borne Limb-Emission Sounder

A superconducting low-noise receiver has been developed for atmospheric observations in the 650-GHz band. A waveguide-type tunerless mixer mount was designed based on one for the 200-GHz band. Two niobium SIS (superconductor-insulator-superconductor) junctions were connected by a tuning inductance to cancel the junction capacitance. We designed the R_nC_j product to be 8 and the current density to be 5.5 kA/cm². The measured receiver noise temperature in DSB was 126-259 K in the frequency range of 618-660 GHz at an IF of 5.2 GHz, and that in the IF band (5-7 GHz) was 126-167 K at 621 GHz. Direct detection measurements using a Fourier transform spectrometer (FTS) showed the frequency response of the SIS mixer to be in the range of about 500-700 GHz. The fractional bandwidth was about 14%. The SIS receiver will be installed in a balloon-borne limb-emission sounder that will be launched from Sanriku Balloon Center in Japan.     

Some recent developments in the design of SIS mixers

SIS mixers in which superconducting tuning elements are integrated with the tunnel junctions have resulted in very low noise heterodyne receivers in the range 68–260 GHz. Above 120 GHz the need for extremely small reduced-height waveguides is avoided by mounting the SIS junctions in a suspended-stripline circuit coupled to a full-height waveguide by a broadband probe. The special characteristics of coplanar transmission line permit the design of SIS mixers with low parasitic reactances. Such a mixer operates over the full WR-10 band (75–110 GHz) without mechanical tuners.An earlier version of this paper was presented at the First International Symposium on Space THz Technology, March, 1990.The National Radio Astronomy Observatory is operated by Associated Universities, Inc., under cooperative agreement with the National Science Foundation.     

A low-noise SIS receiver measured from 480 GHz to 650 GHz using Nb junctions with integrated RF tuning circuits

A heterodyne receiver using an SIS waveguide mixer with two mechanical tuners has been characterized from 480 GHz to 650 GHz. The mixer uses either a single 0.5 × 0.5 µm² Nb/AlO_x/Nb SIS tunnel junction or a series array of two 1 µm² Nb tunnel junctions. These junctions have a high current density, in the range 8 – 13 kA/cm². Superconductive RF circuits are employed to tune the junction capacitance. DSB receiver noise temperatures as low as 200 ± 17 K at 540 GHz, 271 K ± 22 K at 572 GHz and 362 ± 33 K at 626 GHz have been obtained with the single SIS junctions. The series arrays gave DSB receiver noise temperatures as low as 328 ± 26 K at 490 GHz and 336 ± 25 K at 545 GHz. A comparison of the performances of series arrays and single junctions is presented. In addition, negative differential resistance has been observed in the DC I–V curve near 490, 545 and 570 GHz. Correlations between the frequencies for minimum noise temperature, negative differential resistance, and tuning circuit resonances are found. A detailed model to calculate the properties of the tuning circuits is discussed, and the junction capacitance as well as the London penetration depth of niobium are determined by fitting the model to the measured circuit resonances.     

Noise and thermal properties of a submillimeter mixer with the SINS tunnel junction

In this work we present for the first time a low-noise submillimeter receiver with a mixer using Superconductor-Insulator-Normal metal-Superconductor (SINS) junctions. Junctions containing a normal metal layer may be free of the Josephson current and of the related perturbations of mixer operation specific for the standard SIS mixers. This SINS mixer quality is important for the application in the multibeam submillimeter receiver. The SINS mixer stability of operation and independence on the magnetic field have been confirmed in our experiment. Minimum SINS receiver noise in the 290 – 330 GHz band is about 135 K when the junction R_NC is about 30. Noise, conversion gain and thermal properties of the SINS mixer have been studied and compared with the SIS mixers. The limit of SINS mixer operation improvement is discussed at the end of the work.     

A Low-Noise 230 GHz SIS Receiver for Radio Astronomy Employing Untuned Nb/AlOx/Nb Tunnel Junctions

A heterodyne receiver based on a 1/3 reduced height rectangular waveguide SIS mixer with two mechanical tuners has been built for astronomical observations of molecular transitions in the 230 GHz frequency band. The mixer used an untuned array (R_nC_j3, R_n70 ) of four Nb/AIOx/Nb tunnel junctions in series as a nonlinear mixing element. A reasonable balance between the input and output coupling efficiencies has been obtained by choosing the junction number N=4. The receiver exhibits DSB (Double Side Band) noise temperature around 50 K over a frequency range of more than 10 GHz centered at 230 GHz. The lowest system noise temperature of 38 K has been recorded at 232.5 GHz. Mainly by adjusting the subwaveguide backshort, the SSB (Single Side Band) operation with image rejection of 15 dB is obtained with the noise temperature as low as 50 K. In addition, the noise contribution from each receiver component has been studied further. The minimum SIS mixer noise temperature is estimated as 15 K, pretty close to the quantum limit v/k11 K at 230 GHz. It is believed that the receiver noise temperatures presented are the lowest yet reported for a 230 GHz receiver using untuned junctions.     

Analytical prediction for the optimum operating conditions of SIS mixers

Using Tucker's quantum theory of mixing and a quasi five-frequency approximation proposed by Kerr et al., this paper explores the optimum operating conditions of SIS mixers in the frequency region of 100 to 650 GHz. Four parameters (i.e., R_nC_j product, normal state resistance R_n, RF source admittance (R_rf ^–+jB), and IF load resistance R_if) affecting the performance of an SIS mixer have been investigated. Our results indicate that, independent of the absolute value of R_n, the SIS mixer performance is dominated by R_rf/R_n and R_if/R_n; and that the mixer performance becomes quite insensitive to the R_nC_j product, as the mixer operating frequency goes up to submillimeter wavelengths. Concerning all properties of an SIS mixer, the optimum R_rf/R_n value seems proportional to f^1/n (n2), and the optimum R_if/R_n and jB/G_n values are relatively independent of frequency, about 0.5 to 1.5 and –j0.5 to –j1.0 respectively.On leave from Purple Mountain Observatory, China     

A 691 GHz sis receiver for radio astronomy

We report the development of a low noise heterodyne receiver optimized for astronomical observations in the 650 GHz atmospheric window, and specifically for the CO(J=65) line at 691.5 GHz. The system is based on an open structure SIS heterodyne mixer pumped by a continuously tunable solid state oscillator. A niobium SIS junction double array is placed at the end of an integrated V-Antenna. For broad band impedance matching a combination of microstrip impedance transformer and radial stub was used. Receiver noise temperatures of 550 K DSB at 684 GHz were achieved at a 1.8 K physical temperature. The performance improved substantially when decreasing the temperature from 4.2 to 1.8 K. Comparison of model calculations and Fourier transform direct detection measurements of the tuning structure implies that this effect is likely due to the coincidence of operational frequency and the gap frequency of the niobium.     

Nonlinear Response of the Semiconductor Laser with Pump Current Modulation

The influence of tuning the lasing monochromatic radiation frequency _g within the amplification band on the nonlinear response of the semiconductor laser with harmonic modulation of pump current is investigated theoretically. It is established that the principal features of the behavior of the nonlinear amplitude-detuning characteristic (ADC) are determined by the relation between the current modulation frequency _m and the main resonance frequency of the laser _r. If _{m r}, then with increase in _g the response decreases monotonically mainly due to the decrease of its dynamic component. The exception is provided by the spectral regions where peaks on the ADC appear because of the explicitly nonlinear lasing regimes (period doubling, chaos, etc.) When _m < _r, the resonance conditions for induced oscillations are satisfied only for definite spectral intervals within the amplification band and a dip appears on the low-frequency side of the ADC. With decreasing _m, the dip boundary shifts to a more high-frequency region of the band corresponding to smaller local resonance frequencies. The peaks on the ADC corresponding to the radiation period doubling shift to the region of smaller values of _g on increase in _m.     

Photometric and fluorimetric study of the acid-base behavior of 2,2′-diquinolyl and 2,2′,2″-terpyridyl

A photometric and fluorimetric study of the acid-base behavior of 2,2-diquinolyl and 2,2,2-terpyridyl was performed. In sulfuric acid medium, the doubly charged 2,2-diquinolynium ion undergoes the first dissociation atH ₀=0.20±0.09, as determined by fluorimetry (_ex=336 nm, _em=424 nm). Photometric titration is less accurate because of the overlapping of the absorption spectra. The second dissociation constant of 2,2-diquinolyl was determined by fluorimetric titration (_ex=336 nm, _em=420 nm), obtaining a value of 3.67±0.03. The triply charged 2,2,2-terpyridyl molecule was found to undergo the first dissociation atH ₀=–7.17±0.04, as determined by fluorimetric titration (_ex=316 nm, _em=350 nm), in aqueous sulfuric acid medium. Photometric titration (=335 nm) was performed in the presence of 6.5% ethanol because of the low solubility of the compound in water. In this ethanolicwater medium, a value of the dissociation constant atH ₀=–7.39±0.03 was calculated. The second dissociation constant was determined to be 2.81±0.12 by photometric titration at 285 nm, and values of 4.03±0.26 and 4.16±0.20 were found for the third dissociation constant by photometric titrations at 320 and 295 nm, in 10% ethanol, in close agreement with previously reported values. The fluorimetric titration profile obtained by exciting at 274 nm and measuring the fluorescence emission at 350 nm, in the zone betweenH ₀=–3 and pH=10, is complicated by the several equilibria involved.     

SIS quasiparticle mixers with bow-tie antennas

We have designed and evaluated planar lithographed W-band SIS mixers with bow-tie antennas and several different RF cou;ling structures. Both Pb-In-Au/Pb-Bi and Nb/Pb-In-Au junctions were used, each with R_NC«1. Single junctions and series arrays of five junctions directly attached to bow-tie antennas with no additional coupling structure gave poor performance, as expected. Single junctions with inductive microstrips and five-junction arrays with parallel wire inductors gave good coupling over bandwidths of 5 and 25 percent respectively. Good agreement was found between design calculations based on a simple equivalent circuit and measurements of the frequency dependence of the mixer gain. When good coupling was achieved, typical values of mixer gain G_M (DSB)0 dB, noise T_M(DSB)150 K, and receiver noise 200 K were observed. These measurements are referred to the cryostat window. When corrected for the estimated loss between the cryostat window and the antenna terminals, these values of gain are comparable to those observed for W-band waveguide mixers with IF matching, but the noise is significantly higher. There is evidence that 100 K radiation surrounding the mixer reduces the gain and increases the noise. No systematic difference was observed between the performance of Pb-In-Au/Pb-Bi junctions and Nb/Pb-In-Au junctions when the area of the latter was made three times smaller and the current density three times larger so as to maintain the same capacitance and resistance.Work supported by the U.S. Air Force Office of Scientific Research under Grant #AFOSR 85-0230.     

High‐Resolution Submillimeter Wave Spectroscopy of Hydrogen Sulphide with Heterodyne Spectrometer

A submillimeter heterodyne spectrometer using continuous wave optically pumped molecular laser as local oscillator and Schottky diode as mixer was developed at Physical Research Laboratory, Ahmedabad (India) for quantitative spectroscopy of polyatomic molecules in laboratory. The experimental details of spectrometer and its application to study of molecular line parameters are presented. In particular line strength, collision line width (self and foreign) of H₂S 5_5,05_4,1 transition¹(579.799 GHz) have been measured. Air molecules have been used as foreign (perturbing) molecules taking Earths atmosphere into consideration².     

Finite-size effects in a field-theoretic model with long-range exchange interaction

We present a systematic approach to the calculation of finite-size (FS) effects for anO(n) field-theoretic model with both short-range (SR) and long-range (LR) exchange interactions. The LR exchange interaction decays at large distances as 1/r ^d+2–2,0⁺,0⁺. Renormalization group calculations ind=d _u – are performed for a system with a fully finite (block) geometry under periodic boundary conditions. We calculate the FS shift of the critical temperature and the FS renormalized coupling constant of the model to one-loop order. The universal scaling variable is obtained and the FS scaling hypothesis is verified.     

Collective structures of the <Superscript>131</Superscript>Cs nucleus

The collective structures of ¹³¹Cs have been investigated by in-beam -ray spectroscopic techniques following the ¹²⁴Sn (^11B , 4n) reaction at a beam energy E_lab = 57MeV. The previously established rotational bands, built on g_7/2, d_5/2 and the unique-parity h_11/2 orbitals, have been extended and evolve into new bands involving rotationally aligned (h_11/2)² and (h_11/2)² quasiparticles. In addition, a new multiquasiparticle band based on the g_7/2 g_7/2 h_11/2 configuration has also been observed. Theoretical interpretations for the assigned configurations are discussed in the framework of Total Routhian Surface (TRS) and Tilted Axis Cranking (TAC) model calculations. TAC model calculations predict a decrease in the B(M1) values with increasing rotational frequency for the g_7/2/d_5/2 (h_11/2)² and h_11/2 (h_11/2)² bands, thus indicating a magnetic rotation character for these bands.     

High repetition rate CH4 laser

A 16-m CF₄ laser oscillator has operated at 1 kHz in a cooled static cell. Pump energies required from the low pressure, Q-switched, cw discharge CO₂ laser were as low as 60 J. The laser cavity employed a multiple-pass off-axis path resonator in a ring configuration. CF₄ laser power at 615 cm^–1 and a 1-kHz repetition rate exceeded 300 W.     

Simple 1 MM Receivers with a Fixed Tuned Double Sideband SIS Mixer and a Wideband INP MMIC Amplifier

We report on techniques to broaden the intermediate frequency (IF) bandwidth of the BerkeleyIllinoisMaryland Array (BIMA) 1mm SuperconductorInsulatorSuperconductor (SIS) heterodyne receivers by combining fixed tuned Double Side Band (DSB) SIS mixers and wideband Monolithic Microwave Integrated Circuit (MMIC) IF amplifiers. To obtain the flattest receiver gain across the IF band we tested three schemes for keeping the mixer and amplifier as electrically close as possible. In Receiver I, we connected separate mixer and MMIC modules by a 1 stainless steel SMA elbow. In Receiver II, we integrated mixer and MMIC into a modified BIMA mixer module. In Receiver III, we devised a thermally split block in which mixer and MMIC can be maintained at different temperatures–in this receiver module the mixer at 4 K sees very little of the 10–20 mW heat load of the biased MMIC at 10 K. The best average receiver noise we achieved by combining SIS mixer and MMIC amplifier is 45 50 K DSB for _LO = 215–240 GHz and below 80 K DSB for _LO = 205 270 GHz. Over an IF frequency band of 1 – 4 GHz we have demonstrated receiver DSB noise temperatures of 40 – 60 K. Of the three receiver schemes, we feel Receiver III shows the most promise for continued development.     

Deviation from Reference Planes and Reference Misorientation for Σ3 Boundaries

The purpose of the present work is to study the crystallography of a particular family of interfaces, 3 boundaries in copper, in the context of the relationships between 3 plane indices, their deviation from reference planes, and the deviation from exact 3 matching, v/v_m. The relatively high values of v/v_m recorded were considered to be the result of texture development during annealing and various back twinning and 3ⁿ impingement interactions. The results show that there is a reasonable correlation between the deviation from a reference misorientation (v/v_m) and the deviation from reference interface plane (R). Measurement of v/v_m alone provides an indirect estimate of the plane type and hence energy of the boundary, at least for 3 boundaries, and moreover is more germane to the experimental mode of data collection. The effect of intragrain orientation variations on the interface parameters was also studied, and it was shown that there is a 20% difference between misorientations calculated near the interface compared with displaced from the interface.     

A Tuning Circuit with Two Half-Wave Distributed Junctions for All-NbN SIS Mixers

A novel broadband tuning circuit composed of two low-current-density half-wave NbN/MgO/NbN tunnel junctions connected by a half-wave NbN/MgO/NbN microstrip line has been successfully tested in a quasi-optical mixer at frequencies above 700 GHz. The circuit had a designed center frequency of 870 GHz, was integrated in a center-fed twin-slot antenna, and was fed via a quarter-wave impedance transformer. Heterodyne measurments showed double-side-band receiver noise temperatures equivalent to 6-9 quanta from 675 to 810 GHz for a mixer with a current density of 6.7 kA/cm². The RF bandwidth was broader than that of a conventional mixer using a full-wave junction with the same current density.     

230 and 492 GHz low noise sis waveguide receivers employing tuned Nb/AlOx/Nb tunnel junctions

We report results on two full height waveguide receivers that cover the 200–290 GHz and 380–510 GHz atmospheric windows. The receivers are part of the facility instrumentation at the Caltech Submillimeter Observatory on Mauna Kea in Hawaii. We have measured receiver noise temperatures in the range of 20K–35K DSB in the 200–290 GHz band, and 65–90K DSB in the 390–510 GHz atmospheric band. In both instances low mixer noise temperatures and very high quantum efficiency have been achieved. Conversion gain (3 dB) is possible with the 230 GHz receiver, however lowest noise and most stable operation is achieved with unity conversion gain.A 40% operating bandwidth is achieved by using a RF compensated junction mounted in a two-tuner full height waveguide mixer block. The tuned Nb/AlO _x /Nb tunnel junctions incorporate an end-loaded tuning stub with two quarter-wave transformer sections to tune out the large junction capacitance. Both 230 and 492 GHz SIS junctions are 0.49µm² in size and have current densities of 8 and 10 kA/cm² respectively.Fourier Transform Spectrometer (FTS) measurements of the 230 and 492 GHz tuned junctions show good agreement with the measured heterodyne waveguide response.