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Korneeva, Y. P.; Manova, N. N.; Florya, I. N.; Mikhailov, M. Y.; Dobrovolskiy, O. V.; Korneev, A. A.; Vodolazov, D. Y. |
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Title |
Different single-photon response of wide and narrow superconducting MoxSi1−x strips |
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2020 |
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Phys. Rev. Applied |
Abbreviated Journal |
Phys. Rev. Applied |
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13 |
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2 |
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024011 (1 to 7) |
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MoSi SSPD, SNSPD |
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The photon count rate (PCR) of superconducting single-photon detectors made of MoxSi1−x films shaped as a 2-μm-wide strip and a 115-nm-wide meander strip line is studied experimentally as a function of the dc biasing current at different values of the perpendicular magnetic field. For the wide strip, a crossover current Icross is observed, below which the PCR increases with an increasing magnetic field and above which it decreases. This behavior contrasts with the narrow MoxSi1−x meander, for which no crossover current is observed, thus suggesting different photon-detection mechanisms in the wide and narrow strips. Namely, we argue that in the wide strip the absorbed photon destroys superconductivity locally via the vortex-antivortex mechanism for the emergence of resistance, while in the narrow meander superconductivity is destroyed across the whole strip line, forming a hot belt. Accordingly, the different photon-detection mechanisms associated with vortices and the hot belt determine the qualitative difference in the dependence of the PCR on the magnetic field. |
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2331-7019 |
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1790 |
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Neroev, V. V.; Iomdina, E. N.; Khandzhyan, A. T.; Khodzhabekyan, N. V.; Sengaeva, M. D.; Ivanova, A. V.; Seliverstov, S. V.; Teplyakova, K. O.; Goltsman, G. N. |
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Title |
Experimental study of the effect of corneal hydration and its biomechanical properties on the results of photorefractive keratectomy |
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Journal Article |
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Year |
2021 |
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Vestn. Oftalmol. |
Abbreviated Journal |
Vestn. Oftalmol. |
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137 |
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3 |
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68-75 |
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Keywords |
THz scanning, cornea, photorefractive keratectomy, medicine |
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Abstract |
Water content in the cornea may affect the outcome of its excimer laser ablation, especially in presbyopic patients with myopic refraction. This hypothesis can be tested by scanning the cornea in the terahertz (THz) range to determine its hydration level.
Purpose: To study the effect of hydration of the cornea determined by non-contact THz scanning and its biomechanical parameters on the results of photorefractive keratectomy (PRK) in an experiment.
Material and methods: PRK was performed using the Nidek EC-5000 QUEST excimer laser on 8 rabbit eyes. Corneal hydration was evaluated by determining the reflection coefficient (RC) in the THz electromagnetic radiation range before PRK, after 3-5 days, and after 1, 2, 3, and 4 months. Clinical examination included autorefractometry, assessment of corneal thickness and other anatomical and optical parameters of the anterior eye segment (Galilei G6, Ziemer Ophthalmic Systems AG 6.0.2, Switzerland), measurement of corneal hysteresis (CH) and corneal resistance factor (CRF) using the Ocular Response Analyzer (ORA; Reichert, USA), as well as tear production (Schirmer test).
Results: The initial water content in the cornea has a significant effect on the thickness of the removed layer, i.e. on the PRK effect, with correlation coefficient of Rs= -0.976 (p<0.01). The correlation between CH and the ablation depth is less pronounced (Rs=0.643), and CRF had no correlation with it (Rs= -0.089). Biomechanical indicators of the cornea depend on its hydration: changes in CH and CRF after excimer laser ablation qualitatively coincide with changes in RC, the correlation coefficient between RC and the initial value of CH is R= -0.619 (moderate negative correlation).
Conclusion: THz scanning is an effective non-contact technology for monitoring corneal hydration level. The mismatch of the hypoeffect of keratorefractive excimer laser intervention planned for patients with presbyopia with the actual outcome can be caused by individual decrease in the initial water content in the cornea. |
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Russian |
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1794 |
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Smirnov, K.; Moshkova, M.; Antipov, A.; Morozov, P.; Vakhtomin, Y. |
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The cascade switching of the photon number resolving superconducting single-photon detectors |
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Journal Article |
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2021 |
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IEEE Trans. Appl. Supercond. |
Abbreviated Journal |
IEEE Trans. Appl. Supercond. |
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31 |
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2 |
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1-4 |
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PNR SSPD, SNSPD |
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In this article, present the first detailed study of cascade switching in superconducting photon number resolving detectors. The detectors were made in the form of four parallel nanowires, coupled with the single-mode optical fiber and mounted into a closed-cycle refrigerator with a temperature of 2.1 K. We found out the value of additional false pulses (N cas.sw. ) appearing due to cascade switching and showed that it is possible to set up the detector bias current that corresponds to a high level of the detection efficiency and a low level of N cas.sw. simultaneously. We reached the detection efficiency of 60% and N cas.sw. = 0.3%. |
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1051-8223 |
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1796 |
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Pentin, I.; Vakhtomin, Y.; Seleznev, V.; Smirnov, K. |
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Hot electron energy relaxation time in vanadium nitride superconducting film structures under THz and IR radiation |
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Journal Article |
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2020 |
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Sci. Rep. |
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Sci. Rep. |
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10 |
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1 |
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16819 |
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VN HEB |
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The paper presents the experimental results of studying the dynamics of electron energy relaxation in structures made of thin (d approximately 6 nm) disordered superconducting vanadium nitride (VN) films converted to a resistive state by high-frequency radiation and transport current. Under conditions of quasi-equilibrium superconductivity and temperature range close to critical (~ Tc), a direct measurement of the energy relaxation time of electrons by the beats method arising from two monochromatic sources with close frequencies radiation in sub-THz region (omega approximately 0.140 THz) and sources in the IR region (omega approximately 193 THz) was conducted. The measured time of energy relaxation of electrons in the studied VN structures upon heating of THz and IR radiation completely coincided and amounted to (2.6-2.7) ns. The studied response of VN structures to IR (omega approximately 193 THz) picosecond laser pulses also allowed us to estimate the energy relaxation time in VN structures, which was ~ 2.8 ns and is in good agreement with the result obtained by the mixing method. Also, we present the experimentally measured volt-watt responsivity (S~) within the frequency range omega approximately (0.3-6) THz VN HEB detector. The estimated values of noise equivalent power (NEP) for VN HEB and its minimum energy level (deltaE) reached NEP@1MHz approximately 6.3 x 10(-14) W/ radicalHz and deltaE approximately 8.1 x 10(-18) J, respectively. |
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National Research University Higher School of Economics, 20 Myasnitskaya Str., Moscow, 101000, Russia |
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2045-2322 |
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PMID:33033360; PMCID:PMC7546726 |
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1797 |
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Zhang, X.; Lita, A. E.; Smirnov, K.; Liu, H. L.; Zhu, D.; Verma, V. B.; Nam, S. W.; Schilling, A. |
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Strong suppression of the resistivity near the superconducting transition in narrow microbridges in external magnetic fields |
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Journal Article |
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2020 |
Publication |
Phys. Rev. B |
Abbreviated Journal |
Phys. Rev. B |
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Volume |
101 |
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6 |
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060508 (1 to 6) |
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MoSi, WSi films |
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We have investigated a series of superconducting bridges based on homogeneous amorphous WSi and MoSi films, with bridge widths w ranging from 2 to 1000μm and film thicknesses d∼4−6 and 100 nm. Upon decreasing the bridge widths below the respective Pearl lengths, we observe in all cases distinct changes in the characteristics of the resistive transitions to superconductivity. For each of the films, the resistivity curves R(B,T) separate at a well-defined and field-dependent temperature T∗(B) with decreasing the temperature, resulting in a dramatic suppression of the resistivity and a sharpening of the transitions with decreasing bridge width w. The associated excess conductivity in all the bridges scales as 1/w, which may suggest either the presence of a highly conducting region that is dominating the electric transport, or a change in the vortex dynamics in narrow enough bridges. We argue that this effect can only be observed in materials with sufficiently weak vortex pinning. |
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2469-9950 |
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1800 |
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Kitaeva, G. K.; Kornienko, V. V.; Kuznetsov, K. A.; Pentin, I. V.; Smirnov, K. V.; Vakhtomin, Y. B. |
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Direct detection of the idler THz radiation generated by spontaneous parametric down-conversion |
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Journal Article |
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2019 |
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Opt. Lett. |
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Opt. Lett. |
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44 |
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5 |
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1198-1201 |
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HEB applications |
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We study parametric down-conversion (PDC) of optical laser radiation in the strongly frequency non-degenerate regime which is promising for the generation of quantum-correlated pairs of extremely different spectral ranges, the optical and the terahertz (THz) ones. The possibility to detect tenuous THz-frequency photon fluxes generated under low-gain spontaneous PDC is demonstrated using a hot electron bolometer. Then experimental dependences of the THz radiation power on the detection angle and on the pump intensity are analyzed. |
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0146-9592 |
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PMID:30821747 |
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1801 |
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Lobanov, Y. V.; Vakhtomin, Y. B.; Pentin, I. V.; Khabibullin, R. A.; Shchavruk, N. V.; Smirnov, K. V.; Silaev, A. A. |
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Characterization of the THz quantum cascade laser using fast superconducting hot electron bolometer |
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2018 |
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EPJ Web Conf. |
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EPJ Web Conf. |
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195 |
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04004 (1 to 2) |
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NbN HEB, QCL |
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2100-014X |
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3rd International Conference “Terahertz and Microwave Radiation: Generation, Detection and Applications” (TERA-2018) |
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1808 |
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Zolotov, P. I.; Vakhtomin, Yu. B.; Divochiy, A. V.; Seleznev, V. A.; Smirnov, K. V. |
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Technology development of resonator-based structures for efficiency increasing of NBN detectors of IR single photons |
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Journal Article |
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2016 |
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Proc. 5th Int. Conf. Photonics and Information Optics |
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Proc. 5th Int. Conf. Photonics and Information Optics |
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115-116 |
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NbN SSPD |
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This paper presents a technology of fabrication of NbN superconductive single- photon detectors, using resonator structures. The main results are related to optimization of the process of NbN sputtering over substrate with metallic mirrors and SiO 2 /Si 3 N 4 layers /4 thick. Investigation of the quantum efficiency of fabricated devices at 1.6 K on 1.55 μm showed triple-magnified value compared to standard Si/NbN structures. |
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978-5-7262-2215-8 |
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http://fioconf.mephi.ru/files/2015/12/FIO2016-Sbornik.pdf Разработка технологии создания резонаторных структур для увеличения квантовой эффективности NBN детекторов ИК-фотонов |
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1811 |
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Smirnov, K.; Vachtomin, Y.; Divochiy, A.; Antipov, A.; Goltsman, G. |
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The limitation of noise equivalent power by background radiation for infrared superconducting single photon detectors coupled to standard single mode optical fibers |
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2015 |
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Rus. J. Radio Electron. |
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Rus. J. Radio Electron. |
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NbN SSPD |
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We investigated the minimum level of the dark count rates and noise equivalent power of superconducting single photon detectors coupled to standard single mode optical fibers. We found that background radiation limits the minimum level of the dark count rates. We also proposed the effective method for reducing background radiation out of the required spectral range of the detector. Measured noise equivalent power of detector reaches 8.9×10-19 W×Hz1/2 at a wavelength of 1.55 μm and quantum efficiency 35%. |
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14 pages |
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1813 |
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Smirnov, A. V.; Karmantsov, M. S.; Smirnov, K. V.; Vakhtomin, Y. B.; Masterov, D. V.; Tarkhov, M. A.; Pavlov, S. A.; Parafin, A. E. |
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Terahertz response of thin-film YBCO bolometers |
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2012 |
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Tech. Phys. |
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Tech. Phys. |
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57 |
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12 |
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1716-1719 |
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YBCO HEB |
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The bolometric response of high-temperature thin-film YBCO superconducting detectors to an electromagnetic radiation with a frequency of 2.5 THz is measured for the first time. The minimum value of the noise-equivalent power of the detectors is 3.5 × 10−9 W/Hz−−−√. The feasibility of further increasing the sensitivity of the detectors is discussed. |
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