Shurakov, A., Tong, C. - Y. E., Blundell, R., Kaurova, N., Voronov, B., & Gol'tsman, G. (2013). Microwave stabilization of a HEB mixer in a pulse-tube cryocooler. IEEE Trans. Appl. Supercond., 23(3), 1501504.
Abstract: We report the results of our study of the stability of an 800 GHz hot electron bolometer (HEB) mixer cooled with a pulse-tube cryocooler. Pulse-tube cryocoolers introduce temperature fluctuations as well as mechanical vibrations at a frequency of ~1 Hz, both of which can cause receiver gain fluctuations at that frequency. In our system, the motor of the cryocooler was separated from the cryostat to minimize mechanical vibrations, leaving thermal effects as the dominant source of the receiver gain fluctuations. We measured root mean square temperature variations of the 4 K stage of ~7 mK. The HEB mixer was pumped by a solid state local oscillator at 810 GHz. The root mean square current fluctuations at the low noise operating point (1.50 mV, 56.5 μA) were ~0.12 μA, and were predominantly due to thermal fluctuations. To stabilize the bias current, microwave radiation was injected to the HEB mixer. The injected power level was set by a proportional-integral-derivative controller, which completely compensates for the bias current oscillations induced by the pulse-tube cryocooler. Significant improvement in the Allan variance of the receiver output power was obtained, and an Allan time of 5 s was measured.
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Sclafani, M., Marksteiner, M., Keir, F. M. L., Divochiy, A., Korneev, A., Semenov, A., et al. (2012). Sensitivity of a superconducting nanowire detector for single ions at low energy. Nanotechnol., 23(6), 065501 (1 to 5).
Abstract: We report on the characterization of a superconducting nanowire detector for ions at low kinetic energies. We measure the absolute single-particle detection efficiency eta and trace its increase with energy up to eta = 100%. We discuss the influence of noble gas adsorbates on the cryogenic surface and analyze their relevance for the detection of slow massive particles. We apply a recent model for the hot-spot formation to the incidence of atomic ions at energies between 0.2 and 1 keV. We suggest how the differences observed for photons and atoms or molecules can be related to the surface condition of the detector and we propose that the restoration of proper surface conditions may open a new avenue for SSPD-based optical spectroscopy on molecules and nanoparticles.
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Beck, M., Leiderer, P., Kabanov, V. V., Gol'tsman, G., Helm, M., & Demsar, J. (2012). Energy-gap dynamics of a superconductor NbN studied by time-resolved terahertz spectroscopy. In INIS (Vol. 45, pp. 1–3).
Abstract: Using time-resolved terahertz (THz) spectroscopy we performed direct studies of the photoinduced suppression and recovery of the SC gap in a conventional SC NbN. Both processes are found to be strongly temperature and excitation density dependent. The analysis of the data with the established phenomenological Rothwarf-Taylor model enabled us to determine the important microscopic constants: the Cooper pair-breaking rate via phonon absorption and the bare quasiparticle recombination rate. From the latter we were able to extract the dimensionless electron-phonon coupling constant, λ=1.1±0.1, in excellent agreement with theoretical estimates. The technique also allowed us to determine the absorbed energy required to suppress SC, which in NbN equals the thermodynamic condensation energy (in cuprates the two differ by an order of magnitude). Finally, we present the first studies of dynamics following resonant excitation with intense narrow band THz pulses tuned to above and below the superconducting gap. These suggest an additional process, particularly pronounced near Tc, that could be attributed to amplification of SC via effective quasiparticle cooling.
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Pentin, I. V., Smirnov, A. V., Ryabchun, S. A., Gol’tsman, G. N., Vaks, V. L., Pripolzin, S. I., et al. (2011). Heterodyne source of THz range based on semiconductor superlattice multiplier. In IRMMW-THz (pp. 1–2).
Abstract: We present the results of our studies of the possibility of developing a heterodyne receiver incorporating a hot-electron bolometer mixer as the detector and a semiconductor superlattice multiplier driven by a reference synthesizer as the local oscillator. We observe that such a local oscillator offers enough power in the terahertz range to pump the HEB into the operating state.
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Maingault, L., Tarkhov, M., Florya, I., Semenov, A., Espiau de Lamaëstre, R., Cavalier, P., et al. (2010). Spectral dependency of superconducting single photon detectors. J. Appl. Phys., 107(11), 116103 (1 to 3).
Abstract: We investigate the effect of varying both incoming optical wavelength and width of NbN nanowires on the superconducting single photon detectors (SSPD) detection efficiency. The SSPD are current biased close to critical value and temperature fixed at 4.2 K, far from transition. The experimental results are found to verify with a good accuracy predictions based on the “hot spot model,” whose size scales with the absorbed photon energy. With larger optical power inducing multiphoton detection regime, the same scaling law remains valid, up to the three-photon regime. We demonstrate the validity of applying a limited number of measurements and using such a simple model to reasonably predict any SSPD behavior among a collection of nanowire device widths at different photon wavelengths. These results set the basis for designing efficient single photon detectors operating in the infrared (2–5 μm range).
This work was supported by European projects FP6 STREP “SINPHONIA” (Contract No. NMP4-CT-2005-16433) and IP “QAP” (Contract No. 15848).
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de Lara, D. P., Ejrnaes, M., Casaburi, A., Lisitskiy, M., Cristiano, R., Pagano, S., et al. (2008). Feasibility investigation of NbN nanowires as detector in time-of-flight mass spectrometers for macromolecules of interest in biology (proteins). J. Low Temp. Phys., 151(3-4), 771–776.
Abstract: We are investigating the possibility of using NbN nanowires as detectors in time-of-flight mass spectrometers for investigation of macromolecules of interest in biology (proteins). NbN nanowires could overcome the two major drawbacks encountered so far by cryogenic detectors, namely the low working temperature in the mK region and the slow temporal response. In fact, NbN nanowires can work at 5 K and the response time is at least a factor 10–100 better than that of other cryogenic detectors. We present a feasibility study based on a numerical code to calculate the response of a NbN nanowire. The parameter space is investigated at different energies from IR to macromolecules (i.e. from eV to keV) in order to understand if larger value of film thickness and width can be used for the keV energy region. We also present preliminary experimental results of irradiation with X-ray photons of NbN to simulate the effect of macromolecules of the same energy.
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Cherednichenko, S., Drakinskiy, V., Lecomte, B., Dauplay, F., Krieg, J. - M., Delorme, Y., et al. (2008). Terahertz heterodyne array based on NbN HEB mixers. In Proc. 19th Int. Symp. Space Terahertz Technol. (43).
Abstract: A 16 pixel heterodyne receiver for 2.5 THz is been developed based on NbN superconducting hot-electron bolometer (HEB) mixers. The receiver uses a quasioptical RF coupling approach where HEB mixers are integrated into double dipole antennas on 1.5μm thick Si3N4 / SiO2 membranes. Miniature mirrors (one per pixel) and back short for the antenna were used to design the output mixer beam profile. The camera design allows all 16 pixel IF readout in parallel. The gain bandwidth of the HEB mixers on Si3N4 / SiO 2 membranes was found to be about 3 GHz, when an MgO buffer layers is applied on the membrane. We will also present the progress in the camera heterodyne tests.
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Chen, J., Kang, L., Jin, B. B., Xu, W. W., Wu, P. H., Zhang, W., et al. (2008). Properties of terahertz superconducting hot electron bolometer mixers. Int. J. Terahertz Sci. Technol., 1(1), 37–41.
Abstract: A quasi-optical superconducting niobium nitride (NbN) hot electron bolometer (HEB) mixer has been fabricated and measured in the terahertz (THz) frequency range of 0.5~2.52 THz. A receiver noise temperature of 2000 K at 2.52 THz has been obtained for the mixer without corrections. Also, the effect of a Parylene C anti-reflection (AR) coating on the silicon (Si) lens has been studied.
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Cherednichenko, S., Drakinskiy, V., Baubert, J., Lecomte, B., Dauplay, F., Krieg, J. - M., et al. (2007). 2.5 THz multipixel heterodyne receiver based on NbN HEB mixers. In Proc. 18th Int. Symp. Space Terahertz Technol. (112).
Abstract: A 16 pixel heterodyne receiver for 2.5 THz has been developed based on NbN superconducting hot-electron bolometer (HEB) mixers. The receiver uses a quasioptical RF coupling approach where HEB mixers are integrated into double dipole antennas on 1.5μm thick Si3N4 / SiO2 membranes. Spherical mirrors (one per pixel) and backshort distance from the antenna have been used to design the output mixer beam profile. The camera design allows all 16 pixel IF readout in parallel. Measurements of the mixers sensitivity and the input RF band are presented, and compared against calculations.
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Semenov, A., Richter, H., Smirnov, A., Günther, B., Hübers, H. - W., Il’in, K., et al. (2007). Development of HEB mixers for GREAT and for security screening. In Proc. 18th Int. Symp. Space Terahertz Technol. (184).
Abstract: We report the study on the quasioptical coupling efficiency and the gain bandwidth of NbN hot-electron bolometer mixers developed for the 4.7 THz channel of the German receiver for Astronomy at THz-frequencies (GREAT) and for security screening at subterahertz frequencies. Radiation coupling efficiency and directive properties of integrated lens antennas with log-spiral, log-periodic and double-slot planar feeds coupled to a hot-electron bolometer were experimentally studied at frequencies from 1 THz to 6 THz and compared with simulations based on the method of moments and the physical-optics ray tracing. For all studied antennas the modeled spectral dependence of the coupling efficiency fits to the experimental data obtained with both Fourier transform spectroscopy and noise temperature measurements only if the complex impedance of the bolometer is explicitly taken into account. Our experimental data did not indicate any noticeable contribution of the quantum noise to the system noise temperature. The experimentally observed deviation of the beam pattern from the model prediction increases with frequency and is most likely due to a non- ideality of the presently used lenses. Study of the intermediate frequency mixer gain at local oscillator (LO) frequencies between 2.5 THz and 0.3 THz showed an increase of the gain bandwidth at low LO frequencies that was understood as the contribution of the direct interaction of magnetic vortices with the radiation field. We have found that the non- homogeneous hot-spot model more adequately describes variation of the intermediate frequency bandwidth with the applied local oscillator power than any of uniform mixer models. The state-of-the-day performance of the GREAT 4.7-THz channel and the 0.8-THz security scanner will be presented.
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