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Zorin M, Gol'tsman GN, Karasik BS, Elantev AI, Gershenzon EM, Lindgren M, et al. Optical mixing in thin YBa2Cu3O7-x films. IEEE Trans Appl Supercond. 1995;5(2):2431–4.
Abstract: High quality, j/sub c/ (77 K)>10/sup 6/ A/cm/sup 2/, epitaxial YBa2Cu3O7-x films of 50 nm thickness were patterned into ten parallel 1 /spl mu/m wide strips. The film structure was coupled to a single-mode fiber. Mixer response was obtained at 0.78 /spl mu/m using laser frequency modulation and an optical delay line. Using two semiconductor lasers at 1.55 /spl mu/m wavelength the beating signal was used to measure the photoresponse up to 18 GHz. Nonequilibrium photoresponse in the resistive state of the superconductor was observed. Bolometric response dominates up to 3 GHz, after which the nonequilibrium response is constant up to the frequency limit of our registration system. Using an electron heating model the influence of different thermal processes on the conversion loss has been analyzed. Ways of increasing the sensitivity are also discussed.
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Zolotov P, Vakhtomin Y, Divochiy A, Seleznev V, Morozov P, Smirnov K. High-efficiency single-photon detectors based on NbN films.; 2013.
Abstract: We present our resent results in development and testing of Superconducting Single-Photon Detectors (SSPD) with detection efficiencies greater than 85%. High values of obtained results are assigned to proposed design of the detector with integrated resonator structure, including two-layer optical cavity and anti-reflective coating (ARC).
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Zolotov P, Vakhtomin Y, Divochiy A, Morozov P, Seleznev V, Smirnov K. Development of fast and high-effective single-photon detector for spectrum range up to 2.3 μm. In: Proc. SPBOPEN.; 2017. p. 439–40.
Abstract: We present the results of development and testing of the single-photon-counting system operating in the wide spectrum rane up to 2.3 mcm. We managed to increase system detection efficiency up to 60% in the range of 1.7-2.3 mcm optimisation of the fabrication methods of superconducting single-photon detectors and application of the single-mode fiber with enlarged core diameter.
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Zolotov P, Semenov A, Divochiy A, Goltsman G. A comparison of VN and NbN thin films towards optimal SNSPD efficiency. IEEE Trans Appl Supercond. 2021;31(5):1–4.
Abstract: Based on early phenomenological ideas about the operation of superconducting single-photon detectors (SSPD or SNSPD), it was expected that materials with a lower superconducting gap should perform better in the IR range. The plausibility of this concept could be checked using two popular SSPD materials – NbN and WSi films. However, these materials differ strongly in crystallographic structure (polycrystalline B1 versus amorphous), which makes their dependence on disorder different. In our work we present a study of the single-photon response of SSPDs made from two disordered B1 structure superconductors – vanadium nitride and niobium nitride thin films. We compare the intrinsic efficiency of devices made from films with different sheet resistance values. While both materials have a polycrystalline structure and comparable diffusion coefficient values, VN films show metallic behavior over a wide range of sheet resistance, in contrast to NbN films with an insulator-like temperature dependence of resistivity, which may be partially due to enhanced Coulomb interaction, leading to different starting points for the normal electron density of states. The results show that even though VN devices are more promising in terms of theoretical predictions, their optimal performance was not reached due to lower values of sheet resistance.
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Zolotov P, Divochiy A, Vakhtomin Y, Seleznev V, Morozov P, Smirnov K. Superconducting single-photon detectors made of ultra-thin VN films. In: KnE Energy. Vol 3.; 2018. p. 83–9.
Abstract: We optimized technology of thin VN films deposition in order to study VN-based superconducting single-photon detectors. Investigation of the main VN film parameters showed that this material has lower resistivity compared to commonly used NbN. Fabricated from obtained films devices showed 100% intrinsic detection efficiency at 900 nm, at the temperature of 1.7 K starting with the bias current of 0.7·I
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Zolotov P, Divochiy A, Vakhtomin Y, Moshkova M, Morozov P, Seleznev V, et al. Photon-number-resolving SSPDs with system detection efficiency over 50% at telecom range. In: Proc. AIP Conf. Vol 1936.; 2018. 020019.
Abstract: We used technology of making high-efficiency superconducting single-photon detectors as a basis for improvement of photon-number-resolving devices. By adding optical cavity and using an improved NbN superconducting film, we enhanced previously reported system detection efficiency at telecom range for such detectors. Our results show that implementation of optical cavity helps to develop four-section device with quantum efficiency over 50% at 1.55 µm. Performed experimental studies of detecting multi-photon optical pulses showed irregularities over defining multi-photon through single-photon quantum efficiency.
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Zolotov P, Divochiy A, Korneeva Y, Vakhtomin Y, Seleznev V, Smirnov K. Capability investigation of superconducting single-photon detectors, optimized for 800–1200 nm spectrum range.; 2015.
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Zolotov PI, Vakhtomin YB, Divochiy AV, Seleznev VA, Smirnov KV. Technology development of resonator-based structures for efficiency increasing of NBN detectors of IR single photons. Proc 5th Int Conf Photonics and Information Optics. 2016:115–6.
Abstract: 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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Zolotov PI, Semenov AV, Divochiy AV, Goltsman GN, Romanov NR, Klapwijk TM. Dependence of photon detection efficiency on normal-state sheet resistance in marginally superconducting films of NbN. IEEE Trans Appl Supercond. 2021;31(5):1–5.
Abstract: We present an extensive set of data on nanowire-type superconducting single-photon detectors based on niobium-nitride (NbN) to establish the empirical correlation between performance and the normal-state resistance per square. We focus, in particular, on the bias current, compared to the expected depairing current, needed to achieve a near-unity detection efficiency for photon detection. The data are discussed within the context of a model in which the photon energy triggers the movement of vortices i.e. superconducting dissipation, followed by thermal runaway. Since the model is based on the non-equilibrium theory for conventional superconductors deviations may occur, because the efficient regime is found when NbN acts as a marginal superconductor in which long-range phase coherence is frustrated.
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Zolotov PI, Divochiy AV, Vakhtomin YB, Morozov PV, Seleznev VA, Smirnov KV. Development of high-effective superconducting single-photon detectors aimed for mid-IR spectrum range. In: J. Phys.: Conf. Ser. Vol 917.; 2017. 062037.
Abstract: We report on development of superconducting single-photon detectors (SSPD) with high intrinsic quantum efficiency in the wavelength range 1.31 – 3.3 μm. By optimization of the NbN film thickness and its compound, we managed to improve detection efficiency of the detectors in the range up to 3.3 μm. Optimized devices showed intrinsic quantum efficiencies as high as 10% at mid-IR range.
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