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Lobanov YV, Vakhtomin YB, Pentin IV, Rosental VA, Smirnov KV, Goltsman GN, et al. Time-resolved measurements of light–current characteristic and mode competition in pulsed THz quantum cascade laser. Optical Engineering. 2021;60(8):1–8.
Abstract: Quantum cascade lasers (QCL) are widely adopted as prominent and easy-to-use solid-state sources of terahertz radiation. Yet some applications require generation and detection of very sharp and narrow terahertz-range pulses with a specific spectral composition. We have studied time-resolved light-current (L–I) characteristics of multimode THz QCL operated with a fast ramp of the injection current. Detection of THz pulses was carried out using an NbN superconducting hot-electron bolometer with the time constant of the order of 1 ns while the laser bias current was swept during a single driving pulse. A nonmonotonic behavior of the L–I characteristic with several visually separated subpeaks was found. This behavior is associated with the mode competition in THz QCL cavity, which we confirm by L–I measurements with use of an external Fabry–Perot interferometer for a discrete mode selection. We also have demonstrated the possibility to control the L–I shape with suppression of one of the subpeaks by simply adjusting the off-axis parabolic mirror for optimal optical alignment for one of the laser modes. The developed technique paves the way for rapid characterization of pulsed THz QCLs for further studies of the possibilities of using this approach in remote sensing.
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Baksheeva K, Ozhegov R, Goltsman G, Kinev N, Koshelets V, Kochnev A, et al. The sub THz emission of the human body under physiological stress. IEEE Trans Terahertz Sci Technol. 2021.
Abstract: We present evidence that in the sub-THz frequency band, human skin can be considered as an electromagnetic bio-metamaterial, in that its natural emission is a product of skin tissue geometry and embedded structures. Radiometry was performed on 32 human subjects from 480 to 700 GHz. Concurrently, the subjects were exposed to stress, while heart pulse rate (PS) and galvanic skin response (GSR) were also measured. The results are substantially different from the expected black body radiation signal of the skin surface. PS and GSR correlate to the emissivity. Using a simulation model for the skin, we find that the sweat duct is a critical element. The simulated frequency spectra qualitatively match the measured emission spectra and show that our sub-THz emission is modulated by our level of mental stress. This opens avenues for the remote monitoring of the human state.
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Trifonov A, Tong C-YE, Lobanov Y, Kaurova N, Blundell R, Goltsman G. Photon absorption near the gap frequency in a hot electron bolometer. IEEE Trans Appl Supercond. 2017;27(4):1–4.
Abstract: The superconducting energy gap is a fundamental characteristic of a superconducting film, which, together with the applied pump power and the biasing setup, defines the instantaneous resistive state of the Hot Electron Bolometer (HEB) mixer at any given bias point on the I-V curve. In this paper we report on a series of experiments, in which we subjected the HEB to radiation over a wide frequency range along with parallel microwave injection. We have observed three distinct regimes of operation of the HEB, depending on whether the radiation is above the gap frequency, far below it or close to it. These regimes are driven by the different patterns of photon absorption. The experiments have allowed us to derive the approximate gap frequency of the device under test as about 585 GHz. Microwave injection was used to probe the HEB impedance. Spontaneous switching between the superconducting (low resistive) state and a quasi-normal (high resistive) state was observed. The switching pattern depends on the particular regime of HEB operation and can assume a random pattern at pump frequencies below the gap to a regular relaxation oscillation running at a few MHz when pumped above the gap.
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Jiang L, Li J, Zhang W, Yao QJ, Lin ZL, Shi SC, et al. Characterization of NbN HEB mixers cooled by a close-cycled 4 Kelvin refrigerator. IEEE Trans Appl Supercond. 2005;15(2):511–3.
Abstract: It is quite beneficial to operate superconducting hot-electron-bolometer (HEB) mixers with a close-cycled 4 Kelvin refrigerator for real applications such as astronomy and atmospheric research. In this paper, a phononcooled NbN HEB mixer (quasioptical type) is thoroughly characterized under such a cooling circumstance. The effects of mechanical vibration, electrical interference, and temperature fluctuation of a two-stage Gifford-McMahon 4 Kelvin refrigerator upon the characteristics of the phononcooled NbN HEB mixer are investigated in particular. Detailed measurement results are presented.
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Baubert J, Salez M, Merkel H, Pons P, Cherednichenko S, Lecomte B, et al. IF gain bandwidth of membrane-based NbN hot electron bolometers for SHAHIRA. IEEE Trans Appl Supercond. 2005;15(2):507–10.
Abstract: SHAHIRA (Submm Heterodyne Array for HIgh-speed Radio Astronomy) is a project supported by the European Space Agency (ESA) and is designed to fly on the SOFIA observatory. A quasi-optic design has been chosen for 2.5/2.7 THz and 4.7 THz, for hydroxyde radical OH, deuterated hydrogen HD and neutral atomic oxygen OI lines observations. Hot electron bolometers (HEBs) have been processed on 1 /spl mu/m thick SiO/sub 2//Si/sub 3/N/sub 4/ stress-less membranes. In this paper we analyse the intermediate frequency (IF) gain bandwidth from the theoretical point of view, and compare it to measurements.
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Bakhvalova T, Belkin ME, Kovalyuk VV, Prokhodtcov AI, Goltsman GN, Sigov AS. Studying key principles for design and fabrication of silicon photonic-based beamforming networks. In: PIERS-Spring.; 2019. p. 745–51.
Abstract: In the paper, we address key principles for computer-aided design and fabrication of silicon-photonics-based optical beamforming network selecting the optimal approach by simulation and experimental results. To clarify the consideration, the study is conducted on the example of a widely used binary switchable silicon-nitride optical beamforming network based on TriPleX platform. Comparison of simulation results and experimental studies of the prototype shows that the relative error due to technological imperfections does not exceed 3%. According to the estimation, such an error introduces insignificant distortion in the radiation pattern of the referred antenna array.
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Antipov SV, Vachtomin YB, Maslennikov SN, Smirnov KV, Kaurova NS, Grishina EV, et al. Noise performance of quasioptical ultrathin NbN hot electron bolometer mixer at 2.5 and 3.8 THz. In: Proc. 5-th MSMW. Vol 2. Kharkov, Ukraine; 2004. p. 592–4.
Abstract: To put space-based and airborne heterodyne instruments into operation at frequencies above 1 THz the superconducting NbN hot-electron bolometer (HEB) will be incorporated into heterodyne receiver as a mixer. At frequencies above 1.3 THz the sensitivity of the NbN HEB mixers outperform the one of the Schottky diodes and SIS-mixers, and the receiver noise temperature of the NbN HEB mixers increase with frequency. In this paper we present the results of the noise temperature measurements within one batch of NbN HEB mixers based on 3.5 mn thick superconducting NbN film grown on Si substrate with MgO buffer layer at the LO frequencies 2.5 THz and 3.8 THz.
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Korneev A, Kovalyuk V, Ferrari S, Kahl O, Pernice W, An P, et al. Superconducting Single-Photon Detectors for Integrated Nanophotonics Circuits. In: 16th ISEC.; 2017. p. 1–3.
Abstract: We present an overview of our recent achievements in integration of superconducting nanowire single-photon detectors SNSPD with dielectric optical waveguides. We are able to produce complex nanophotonics integrated circuits containing optical elements and photon detector on single chip thus producing a compact integrated platform for quantum optics applications.
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Goltsman G. Superconducting thin film as infrared heterodyne and direct detectors. In: 16th ISEC.; 2017. p. 1–3.
Abstract: We present our recent achievements in the development of superconducting nanowire single-photon detectors (SNSPDs) integrated with optical waveguides on a chip. We demonstrate both single-photon counting with up to 90% on-chip-quantum-efficiency (OCDE), and the heterodyne mixing with a close to the quantum limit sensitivity at the telecommunication wavelength using single device.
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Tretyakov I, Svyatodukh S, Chumakova A, Perepelitsa A, Kaurova N, Shurakov A, et al. Room temperature silicon detector for IR range coated with Ag2S quantum dots. In: IRMMW-THz.; 2019.
Abstract: A silicon has been the chief technological semiconducting material of modern microelectronics and has had a strong influence on all aspects of society. Applications of Si-based optoelectronic devices are limited to the visible and near infrared ranges. The expansion of the Si absorption to shorter wavelengths of the infrared range is of considerable interest to optoelectronic applications. By creating impurity states in Si it is possible to cause sub-band gap photon absorption. Here, we present an elegant and effective technology of extending the photoresponse of towards the IR range. Our approach is based on the use of Ag 2 S quantum dots (QDs) planted on the surface of Si. The specific sensitivity of the Ag 2 S/Si heterostructure is 10 11 cm√HzW -1 at 1.55μm. Our findings open a path towards the future study and development of Si detectors for technological applications.
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