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Iomdina, E. N., Goltsman, G. N., Seliverstov, S. V., Sianosyan, A. A., Teplyakova, K. O., & Rusova, A. A. (2016). Study of transmittance and reflectance spectra of the cornea and the sclera in the THz frequency range. J. Biomed. Opt., 21(9), 97002 (1 to 5).
Abstract: An adequate water balance (hydration extent) is one of the basic factors of normal eye function, including its external shells: the cornea and the sclera. Adequate control of corneal and scleral hydration is very important for early diagnosis of a variety of eye diseases, stating indications for and contraindications against keratorefractive surgeries and the choice of contact lens correction solutions. THz systems of creating images in reflected beams are likely to become ideal instruments of noninvasive control of corneal and scleral hydration degrees. This paper reports on the results of a study involving transmittance and reflectance spectra for the cornea and the sclera of rabbit and human eyes, as well as those of the rabbit eye, in the frequency range of 0.13 to 0.32 THz. The dependence of the reflectance coefficient of these tissues on water mass percentage content was determined. The experiments were performed on three corneas, three rabbit scleras, two rabbit eyes, and three human scleras. The preliminary results demonstrate that the proposed technique, based on the use of a continuous THz radiation, may be utilized to create a device for noninvasive control of corneal and scleral hydration, which has clear potential of broad practical application.
Keywords: BWO, IMPATT diode, Schottky diode, medicine, animals, cornea, physiology, humans, rabbits, sclera diagnostic imaging, physiology
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Gayduchenko, I. A., Fedorov, G. E., Stepanova, T. S., Titova, N., Voronov, B. M., But, D., et al. (2016). Asymmetric devices based on carbon nanotubes as detectors of sub-THz radiation. In J. Phys.: Conf. Ser. (Vol. 741, 012143 (1 to 6)).
Abstract: Demand for efficient terahertz (THz) radiation detectors resulted in intensive study of the asymmetric carbon nanostructures as a possible solution for that problem. In this work, we systematically investigate the response of asymmetric carbon nanodevices to sub-terahertz radiation using different sensing elements: from dense carbon nanotube (CNT) network to individual CNT. We conclude that the detectors based on individual CNTs both semiconducting and quasi-metallic demonstrate much stronger response in sub-THz region than detectors based on disordered CNT networks at room temperature. We also demonstrate the possibility of using asymmetric detectors based on CNT for imaging in the THz range at room temperature. Further optimization of the device configuration may result in appearance of novel terahertz radiation detectors.
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Seliverstov, S. V., Rusova, A. A., Kaurova, N. S., Voronov, B. M., & Goltsman, G. N. (2016). Attojoule energy resolution of direct detector based on hot electron bolometer. In J. Phys.: Conf. Ser. (Vol. 741, 012165 (1 to 5)). IOP Publishing.
Abstract: We characterize superconducting antenna-coupled NbN hot-electron bolometer (HEB) for direct detection of THz radiation operating at a temperature of 9.0 K. At signal frequency of 2.5 THz, the measured value of the optical noise equivalent power is 2.0×10-13 W-Hz-0.5. The estimated value of the energy resolution is about 1.5 aJ. This value was confirmed in the experiment with pulsed 1.55-μm laser employed as a radiation source. The directly measured detector energy resolution is 2 aJ. The obtained risetime of pulses from the detector is 130 ps. This value was determined by the properties of the RF line. These characteristics make our detector a device-of-choice for a number of practical applications associated with detection of short THz pulses.
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Korneeva, Y., Sidorova, M., Semenov, A., Krasnosvobodtsev, S., Mitsen, K., Korneev, A., et al. (2016). Comparison of hot-spot formation in NbC and NbN single-photon detectors. IEEE Trans. Appl. Supercond., 26(3), 1–4.
Abstract: We report an experimental investigation of the hot-spot evolution in superconducting single-photon detectors made of disordered superconducting materials with different diffusivity and energy downconversion time values, i.e., 33-nm-thick NbN and 23-nm-thick NbC films. We have demonstrated that, in NbC film, only 405-nm photons produce sufficiently large hot spot to trigger a single-photon response. The dependence of detection efficiency on bias current for 405-nm photons in NbC is similar to that for 3400-nm photons in NbN. In NbC, large diffusivity and downconversion time result in 1-D critical current suppression profile compared with the usual 2-D profile in NbN.
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Ferrari, S., Kahl, O., Kovalyuk, V., Goltsman, G. N., Korneev, A., & Pernice, W. H. P. (2015). Waveguide-integrated single- and multi-photon detection at telecom wavelengths using superconducting nanowires. Appl. Phys. Lett., 106(15), 151101 (1 to 5).
Abstract: We investigate single- and multi-photon detection regimes of superconducting nanowire detectors embedded in silicon nitride nanophotonic circuits. At near-infrared wavelengths, simultaneous detection of up to three photons is observed for 120 nm wide nanowires biased far from the critical current, while narrow nanowires below 100 nm provide efficient single photon detection. A theoretical model is proposed to determine the different detection regimes and to calculate the corresponding internal quantum efficiency. The predicted saturation of the internal quantum efficiency in the single photon regime agrees well with plateau behavior observed at high bias currents.
W. H. P. Pernice acknowledges support by the DFG Grant Nos. PE 1832/1-1 and PE 1832/1-2 and the Helmholtz society through Grant No. HIRG-0005. The Ph.D. education of O. Kahl is embedded in the Karlsruhe School of Optics and Photonics (KSOP). G. N. Goltsman acknowledges support by Russian Federation President Grant HШ-1918.2014.2 and Ministry of Education and Science of the Russian Federation Contract No.: RFMEFI58614X0007. A. Korneev acknowledges support by Statement Task No. 3.1846.2014/k. V. Kovalyuk acknowledges support by Statement Task No. 2327. We also acknowledge support by the Deutsche Forschungsgemeinschaft (DFG) and the State of Baden-Württemberg through the DFG-Center for Functional Nanostructures (CFN) within subproject A6.4. We thank S. Kühn and S. Diewald for the help with device fabrication as well as B. Voronov and A. Shishkin for help with NbN thin film deposition and A. Semenov for helpful discussion about the detection mechanism of nanowire SSPD's.
The authors declare no competing financial interests.
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Kahl, O., Ferrari, S., Kovalyuk, V., Goltsman, G. N., Korneev, A., & Pernice, W. H. P. (2015). Waveguide integrated superconducting single-photon detectors with high internal quantum efficiency at telecom wavelengths. Sci. Rep., 5, 10941 (1 to 11).
Abstract: Superconducting nanowire single-photon detectors (SNSPDs) provide high efficiency for detecting individual photons while keeping dark counts and timing jitter minimal. Besides superior detection performance over a broad optical bandwidth, compatibility with an integrated optical platform is a crucial requirement for applications in emerging quantum photonic technologies. Here we present efficiencies close to unity at 1550nm wavelength. This allows for the SNSPDs to be operated at bias currents far below the critical current where unwanted dark count events reach milli-Hz levels while on-chip detection efficiencies above 70% are maintained. The measured dark count rates correspond to noiseequivalent powers in the 10–19W/Hz–1/2 range and the timing jitter is as low as 35ps. Our detectors are fully scalable and interface directly with waveguide-based optical platforms.
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Seliverstov, S., Maslennikov, S., Ryabchun, S., Finkel, M., Klapwijk, T. M., Kaurova, N., et al. (2015). Fast and sensitive terahertz direct detector based on superconducting antenna-coupled hot electron bolometer. IEEE Trans. Appl. Supercond., 25(3), 2300304.
Abstract: We characterize superconducting antenna-coupled hot-electron bolometers for direct detection of terahertz radiation operating at a temperature of 9.0 K. The estimated value of responsivity obtained from lumped-element theory is strongly different from the measured one. A numerical calculation of the detector responsivity is developed, using the Euler method, applied to the system of heat balance equations written in recurrent form. This distributed element model takes into account the effect of nonuniform heating of the detector along its length and provides results that are in better agreement with the experiment. At a signal frequency of 2.5 THz, the measured value of the optical detector noise equivalent power is 2.0 × 10-13 W · Hz-0.5. The value of the bolometer time constant is 35 ps. The corresponding energy resolution is about 3 aJ. This detector has a sensitivity similar to that of the state-of-the-art sub-millimeter detectors operating at accessible cryogenic temperatures, but with a response time several orders of magnitude shorter.
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Korneev, A. A., Korneeva, Y. P., Mikhailov, M. Y., Pershin, Y. P., Semenov, A. V., Vodolazov, D. Y., et al. (2015). Characterization of MoSi superconducting single-photon detectors in the magnetic field. IEEE Trans. Appl. Supercond., 25(3), 2200504 (1 to 4).
Abstract: We investigate the response mechanism of nanowire superconducting single-photon detectors (SSPDs) made of amorphous MoxSi1-x. We study the dependence of photon count and dark count rates on bias current in magnetic fields up to 113 mT at 1.7 K temperature. The observed behavior of photon counts is similar to the one recently observed in NbN SSPDs. Our results show that the detecting mechanism of relatively high-energy photons does not involve the vortex penetration from the edges of the film, and on the contrary, the detecting mechanism of low-energy photons probably involves the vortex penetration from the film edges.
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Gayduchenko, I., Kardakova, A., Fedorov, G., Voronov, B., Finkel, M., Jiménez, D., et al. (2015). Response of asymmetric carbon nanotube network devices to sub-terahertz and terahertz radiation. J. Appl. Phys., 118(19), 194303.
Abstract: Demand for efficient terahertz radiation detectors resulted in intensive study of the asymmetric carbon nanostructures as a possible solution for that problem. It was maintained that photothermoelectric effect under certain conditions results in strong response of such devices to terahertz radiation even at room temperature. In this work, we investigate different mechanisms underlying the response of asymmetric carbon nanotube (CNT) based devices to sub-terahertz and terahertz radiation. Our structures are formed with CNT networks instead of individual CNTs so that effects probed are more generic and not caused by peculiarities of an individual nanoscale object. We conclude that the DC voltage response observed in our structures is not only thermal in origin. So called diode-type response caused by asymmetry of the device IV characteristic turns out to be dominant at room temperature. Quantitative analysis provides further routes for the optimization of the device configuration, which may result in appearance of novel terahertz radiation detectors.
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Goltsman, G. N., Samartsev, V. V., Vinogradov, E. A., Naumov, A. V., & Karimullin, K. R. (2015). New generation of superconducting nanowire single-photon detectors. In EPJ Web of Conferences (Vol. 103, 01006 (1 to 2)).
Abstract: We present an overview of recent results for new generation of infrared and optical superconducting nanowire single-photon detectors (SNSPDs) that has already demonstrated a performance that makes them devices-of-choice for many applications. SNSPDs provide high efficiency for detecting individual photons while keeping dark counts and timing jitter minimal. Besides superior detection performance over a broad optical bandwidth, SNSPDs are also compatible with an integrated optical platform as a crucial requirement for applications in emerging quantum photonic technologies. By embedding SNSPDs in nanophotonic circuits we realize waveguide integrated single photon detectors which unite all desirable detector properties in a single device.
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Galin, M. A., Klushin, A. M., Kurin, V. V., Seliverstov, S. V., Finkel, M. I., Goltsman, G. N., et al. (2015). Towards local oscillators based on arrays of niobium Josephson junctions. Supercond. Sci. Technol., 28(5), 055002 (1 to 7).
Abstract: Various applications in the field of terahertz technology are in urgent need of compact, wide-tunable solid-state continuous wave radiation sources with a moderate power. However, satisfactory solutions for the THz frequency range are scarce yet. Here we report on coherent radiation from a large planar array of Josephson junctions (JJs) in the frequency range between 0.1 and 0.3 THz. The external resonator providing the synchronization of JJ array is identified as a straight fragment of a single-strip-line containing the junctions themselves. We demonstrate a prototype of the quasioptical heterodyne receiver with the JJ array as a local oscillator and a hot-electron bolometer mixer.
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Florya, I. N., Korneeva, Y. P., Sidorova, M. V., Golikov, A. D., Gaiduchenko, I. A., Fedorov, G. E., et al. (2015). Energy relaxtation and hot spot formation in superconducting single photon detectors SSPDs. In EPJ Web of Conferences (Vol. 103, 10004 (1 to 2)).
Abstract: We have studied the mechanism of energy relaxation and resistive state formation after absorption of a single photon for different wavelengths and materials of single photon detectors. Our results are in good agreement with the hot spot model.
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Shurakov, A., Lobanov, Y., & Goltsman, G. (2015). Superconducting hot-electron bolometer: from the discovery of hot-electron phenomena to practical applications. Supercond. Sci. Technol., 29(2), 023001.
Abstract: The discovery of hot-electron phenomena in a thin superconducting film in the last century was followed by numerous experimental studies of its appearance in different materials aiming for a better understanding of the phenomena and consequent implementation of terahertz detection systems for practical applications. In contrast to the competitors such as superconductor-insulator-superconductor tunnel junctions and Schottky diodes, the hot electron bolometer (HEB) did not demonstrate any frequency limitation of the detection mechanism. The latter, in conjunction with a decent performance, rapidly made the HEB mixer the most attractive candidate for heterodyne observations at frequencies above 1 THz. The successful operation of practical instruments (the Heinrich Hertz Telescope, the Receiver Lab Telescope, APEX, SOFIA, Hershel) ensures the importance of the HEB technology despite the lack of rigorous theoretical routine for predicting the performance. In this review, we provide a summary of experimental and theoretical studies devoted to understanding the HEB physics, and an overview of various fabrication routes and materials.
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Tretyakov, I., Maslennikov, S., Semenov, A., Safir, O., Finkel, M., Ryabchun, S., et al. (2015). Impact of operating conditions on noise and gain bandwidth of NbN HEB mixers. In Proc. 26th Int. Symp. Space Terahertz Technol. (39).
Abstract: Hot-electron bolometer mixers (HEB’s) are the most promising devices as mixing element for terahertz spectroscopy and astronomy at frequencies beyond 1.4 THz. They have a low noise temperature and low demands on local oscillator (LO) power. 1,2 An important limitation is the IF bandwidth, of the order of a few GHz, and which in principle depends on energy relaxation due to electron- phonon processes and on diffusion-cooling. It has been proposed by Prober that a reduction in length of the HEB would lead to an increased bandwidth. 3 This appeared to be achieved by Tretyakov et al by measuring the gain bandwidth close to the critical temperature of the NbN. 2 Unfortunately, the noise bandwidth of similar devices operated at temperatures around 4.2 K appear not depend on the length. The fundamental problem to be addressed is the position-dependent superconducting state of the HEB- devices under operating conditions, which determines the conditions for the cooling of the hot quasiparticles. Some progress has been made by Barends et al in a semi-empirical model to describe the I,V curves under operating conditions at a bath temperature around 4.2 K. 4 In more recent work Vercruyssen et al have analyzed the I,V curve, without any LO-equivalent bias, of a model NSN system. 5 This work suggests that the most appropriate model for an HEB under operating conditions is that of a potential-well in the superconducting gap in the center of the NbN, analogous the bimodal superconducting state described by Vercruyssen et al. Hot quasiparticles in the well can not diffuse out and can only cool by electron-phonon processes, those with higher energies than the heights of the walls of the well can diffuse out. Using this working hypothesis we have carried out experiments on a sub-micrometer NbN bridge connected to a gold (Au) planar spiral antenna. An in situ process is used to deposit Au on NbN. The Au is removed in the center to define the uncovered NbN, which will act as the superconducting mixer itself. The antenna is deposited on the remaining Au layer on the NbN. The Au contacts suppress the energy gap of the NbN film located underneath the gold layer 7,8 . The measured resistive transition is shown in Fig.1. It clearly shows a T c of the bilayer at 6.2 K and the resistive transition of the NbN itself around 9 K. In addition we show the measured noise bandwidth (red squares) for different bath temperatures. Clearly the noise bandwidth increases strongly by increasing the bath temperature from 5 K to 8 K, up to 13 GHz. We interpret this pattern as evidence for improved out-diffusion of hot electrons due to normal banks and a shallow superconducting potential well compared to k B T. As expected the noise temperature in this regime is much bigger than when biased at 4.2 K. R EFERENCES 1 W. Zhang, P. Khosropanah, J. R. Gao, E. L. Kollberg, K. S. Yngvesson, T. Bansal, R. Barends, and T. M. Klapwijk Appl. Phys. Lett. 96, 111113, (2010). 2 Ivan Tretyakov, Sergey Ryabchun, Matvey Finkel, Anna Maslennikova, Natalia Kaurova, Anastasia Lobastova, Boris Voronov, and Gregory Gol’tsman Appl. Phys. Lett. 98, 033507 (2011). 3 D. E. Prober, Appl. Phys. Lett. 62, 2119 (1992). 4 R. Barends, M. Hajenius, J. R. Gao, and T. M. Klapwijk, Appl. Phys. Lett. 87, 263506 (2005). 5 N. Vercruyssen, T. G. A. Verhagen, M. G. Flokstra, J. P. Pekola, and T. M. Klapwijk Physical Review B 85, 224503 (2012).
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Kardakova, A. I., Coumou, P. C. J. J., Finkel, M. I., Morozov, D. V., An, P. P., Goltsman, G. N., et al. (2015). Electron–phonon energy relaxation time in thin strongly disordered titanium nitride films. IEEE Trans. Appl. Supercond., 25(3), 1–4.
Abstract: We have measured the energy relaxation times from the electron bath to the phonon bath in strongly disordered TiN films grown by atomic layer deposition. The measured values of τ eph vary from 12 to 91 ns. Over a temperature range from 3.4 to 1.7 K, they follow T -3 temperature dependence, which are consistent with values of τ eph reported previously for sputtered TiN films. For the most disordered film, with an effective elastic mean free path of 0.35 nm, we find a faster relaxation and a stronger temperature dependence, which may be an additional indication of the influence of strong disorder on a superconductor.
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