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Iomdina EN, Seliverstov SV, Sianosyan AA, Teplyakova KO, Rusova AA, Goltsman GN. Terahertz scanning for evaluation of corneal and scleral hydration. STM. 2018;10(4):143–9.
Abstract: The aim of the investigation was to study the prospects of using continuous THz scanning of the cornea and the sclera to determine water concentration in these tissues and on the basis of the obtained data to develop the experimental installation for monitoring corneal and scleral hydration degree.Materials and Methods. To evaluate corneal and scleral transmittance and reflectance spectra in the THz range, the developed experimental installations were used to study 3 rabbit corneas and 3 scleras, 2 whole rabbit eyes, and 3 human scleras. Besides, two rabbit eyes were studied in vivo prior to keratorefractive surgery as well as 10 and 21 days following the surgery (LASIK).Results. There have been created novel experimental installations enabling in vitro evaluation of frequency dependence of corneal and scleral transmittance coefficients and reflectance coefficients on water percentage in the THz range. Decrease in corneal water content by 1% was found to lead to reliably established decrease in the reflected signal by 13%. The reflectance spectrum of the whole rabbit eye was measured in the range of 0.13–0.32 THz. The study revealed the differences between the indices of rabbit cornea and sclera, as well as rabbit and human sclera. There was developed a laboratory model of the installation for in vivo evaluation of corneal and scleral hydration using THz radiation.Conclusion. The preliminary findings show that the proposed technique based on the use of continuous THz radiation can be employed to create a device for noninvasive control of corneal and scleral hydration.
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Florya IN, Korneeva YP, Mikhailov MY, Devizenko AY, Korneev AA, Goltsman GN. Photon counting statistics of superconducting single-photon detectors made of a three-layer WSi film. Low Temp Phys. 2018;44(3):221–5.
Abstract: Superconducting nanowire single-photon detectors (SNSPD) are used in quantum optics when record-breaking time resolution, high speed, and exceptionally low levels of dark counts (false readings) are required. Their detection efficiency is limited, however, by the absorption coefficient of the ultrathin superconducting film for the detected radiation. One possible way of increasing the detector absorption without limiting its broadband response is to make a detector in the form of several vertically stacked layers and connect them in parallel. For the first time we have studied single-photon detection in a multilayer structure consisting of three superconducting layers of amorphous tungsten silicide (WSi) separated by thin layers of amorphous silicon. Two operating modes of the detector are illustrated: an avalanche regime and an arm-trigger regime. A shift in these modes occurs at currents of ∼0.5–0.6 times the critical current of the detector.
This work was supported by technical task No. 88 for scientific research at the National Research University “Higher School of Economics,” Grant No. 14.V25.31.0007 from the Ministry of Education and Science of Russia, and the work of G. N. Goltsman was supported by task No. 3.7328.2017/VU of the Ministry of Education and Science of Russia.
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Райтович АА, Пентин ИВ, Золотов ФИ, Селезнев ВА, Вахтомин ЮБ, Смирнов КВ. Время энергетической релаксации электронов в сверхпроводниковых VN наноструктурах. In: Сборник трудов 13 Всероссийской конференции молодых ученых. Техно-Декор; 2018. p. 236–8.
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Sych D, Shcherbatenko M, Elezov M, Goltsman GN. Towards the improvement of the heterodyne receiver sensitivity beyond the quantum noise limit. In: Proc. 29th Int. Symp. Space Terahertz Technol.; 2018. p. 245–7.
Abstract: Noise reduction in heterodyne receivers of the terahertz range is an important issue for astronomical applications. Quantum fluctuations, also known as shot noise, prohibit errorless measurements of the amplitude of electro-magnetic waves, and introduce the so-called standard quantum limit (SQL) on the minimum error of the heterodyne measurements. Nowadays, the sensitivity of modern heterodyne receivers approaches the SQL, and the growing demand for the improvement of measurement precision stimulates a number of both theoretical and experimental efforts to design novel measurement techniques aimed at overcoming the SQL. Here we demonstrate the first steps towards the practical implementation of a sub-SQL quantum receiver. As the principal resources, it requires a highly efficient single-photon counting detector and an interferometer-based scheme for mixing the signal with a low-power local oscillator. We describe the idea of such receiver and its main components.
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Nikoghosyan AS, Martirosyan RM, Hakhoumian AA, Makaryan AH, Tadevosyan VR, Goltsman GN, et al. Effect of absorption on the efficiency of THz radiation generation in a nonlinear crystal placed into a waveguide. Armenian J Phys. 2018;11(4):257–62.
Abstract: The effect of THz radiation absorption on the efficiency of generation of coherent THz radiation in a nonlinear optical crystal placed into a metal rectangular waveguide is studied. The efficiency of the nonlinear conversion of optical laser radiation to the THz band is also a function of the phase-matching (PM) condition inside the nonlinear crystal. The method of partial filling of a metal waveguide with a nonlinear optical crystal is used to ensure phase matching. Phase matching was obtained by the proper choice of the thickness of the nonlinear crystal, namely the degree of partial filling of the waveguide. We have studied the THz radiation attenuation caused by the losses in both the metal walls of the waveguide and in the crystal, taking into account the dimension of the cross section of the waveguide, the degree of partial filling and its dielectric constant.
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Kuznetsov KA, Kornienko VV, Vakhtomin YB, Pentin IV, Smirnov KV, Kitaeva GK. Generation and detection of optical-terahertz biphotons via spontaneous parametric downconversion. In: Proc. ICLO.; 2018. 303.
Abstract: We study spontaneous parametric downconversion (SPDC) in the strongly non-degenerate regime when the idler wave hits the terahertz range. By using the hot-electron bolometer, for the first time the SPDC-generated idler-wave photons were directly detected in the terahertz frequency range. Spectrum of corresponding signal photons was measured using standard technique by the CCD camera. Possible applications of correlated optical-terahertz biphotons are discussed.
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Мошкова МА, Дивочий АВ, Морозов ПВ, Золотов ФИ, Вахтомин ЮБ, Смирнов КВ. Высокоэффективные NBN однофотонные детекторы с разрешением числа фотонов. In: Сборн. науч. труд. VII международн. конф. по фотонике и информац. опт.; 2018. p. 400–1.
Abstract: Разработаны и исследованы сверхпроводниковые однофотонные детекторы, способные к разрешению до 3-х фотонов в коротком импульсе излучения и имеющие квантовую эффективность детектирования одиночных фотонов ~60% на длине волны lambda=1.55 мкм. Проведенная модернизация технологии изготовления детекторов, позволила получить приемные устройства с мультифотонной квантовой эффективностью, приближающейся к расчетным значениям.
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Симонов НО, Флоря ИН, Корнеева ЮП, Корнеев АА, Гольцман ГН. Однофотонный отклик в тонких сверхпроводящих MoNx пленках. In: Сборн. науч. труд. VII международн. конф. по фотонике и информац. опт.; 2018. p. 408–9.
Abstract: Продемонстрирован однофотонный отклик, при токе близком к критическому, в MoNx сверхпроводящих полосках шириной 70-104 нм. MoNx детекторы, имеющие коэффициент диффузии D≈0.32 см2/с и время электрон-фононного взаимодействия ηe-ph≈300 пс, достигают квантовой эффективности QE≈20% на длине волны λ=1550 нм. Возможность реализации однофотонного детектора в данном материале, подтверждает существующую теорию вихревого механизма возникновения фотоотклика в узких сверхпроводящих полосках.
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Eletskii AV, Sarychev AK, Boginskaya IA, Bocharov GS, Gaiduchenko IA, Egin MS, et al. Amplification of a Raman scattering signal by carbon nanotubes. Dokl Phys. 2018;63(12):496–8.
Abstract: The effect of Raman scattering (RLS) signal amplification by carbon nanotubes (CNTs) was studied. Single-layered nanotubes were synthesized by the chemical vapor deposition (CVD) method using methane as a carbon-containing gas. The object of study used was water, the Raman spectrum of which is rather well known. Amplification of the Raman scattering signal by several hundred percent was attained in our work. The maximum amplification of a Raman scattering signal was shown to be achieved at an optimal density of nanotubes on a substrate. This effect was due to the scattering and screening of plasmons excited in CNTs by neighboring nanotubes. The amplification mechanism and the possibilities of optimization for this effect were discussed on the basis of the theory of plasmon resonance in carbon nanotubes.
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Tretyakov IV, Anfertyev VA, Revin LS, Kaurova NS, Voronov BM, Vaks VL, et al. Sensitivity and resolution of a heterodyne receiver based on the NbN HEB mixer with a quantum-cascade laser as a local oscillator. Radiophys Quant Electron. 2018;60(12):988–92.
Abstract: We present the results of experimental studies of the basic characteristics and operation features of a terahertz heterodyne detector based on the superconducting NbN HEB mixer and a quantum cascade laser as a local oscillator operating at a frequency of 2.02 THz. The measured noise temperature of such a mixer amounted to 1500 K. The spectral resolution of the detector is determined by the width of the local-oscillator spectral line whose measured value does not exceed 1 MHz. The quantum-cascade laser could be linearly tuned with respect to frequency with the coefficient 7.2 MHz/mA within the limits of the current oscillation bandwidth.
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