Neroev, V. V., Iomdina, E. N., Khandzhyan, A. T., Khodzhabekyan, N. V., Sengaeva, M. D., Ivanova, A. V., et al. (2021). Experimental study of the effect of corneal hydration and its biomechanical properties on the results of photorefractive keratectomy. Vestn. Oftalmol., 137(3), 68–75.
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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Moshkova, M. A., Morozov, P. V., Antipov, A. V., Vakhtomin, Y. B., & Smirnov, K. V. (2021). High-efficiency multi-element superconducting single-photon detector. In I. Prochazka, M. Štefaňák, R. Sobolewski, & A. Gábris (Eds.), Proc. SPIE (Vol. 11771, pp. 2–8). SPIE.
Abstract: We present the result of the creation and investigation of the multi-element superconducting single photon detectors, which can recognize the number of photons (up to six) in a short pulse of the radiation at telecommunication wavelengths range. The best receivers coupled with single-mode fiber have the system quantum efficiency of ⁓85%. The receivers have a 100 ps time resolution and a few nanoseconds dead time that allows them to operate at megahertz counting rate. Implementation of the multi-element architecture for creation of the superconducting single photon detectors with increased sensitive area allows to create the high efficiency receivers coupled with multi-mode fibers and with preserving of the all advantages of superconducting photon counters.
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Moshkova, M. A., Divochiy, A. V., Morozov, P. V., Antipov, A. V., Vakhtomin, Y. B., & Smirnov, K. V. (2019). Characterization of topologies of superconducting photon number resolving detectors. In Proc. 8th Int. Conf. Photonics and Information Optics (pp. 465–466).
Abstract: Comparative analysis for different topologies of superconducting single-photon detectors with ability to resolve up to 4 photons in a short pulse of IR radiation has been carry out. It was developed the detector with a system detection efficiency of ~ 85 % at λ = 1550 nm. The possibility of using such detector to restore photon statistics of a pulsed radiation source was demonstrated.
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Morozov, D. V., Smirnov, K. V., Smirnov, A. V., Lyakhov, V. A., & Goltsman, G. N. (2005). A millimeter-submillimeter phonon-cooled hot-electron bolometer mixer based on two-dimensional electron gas in an AlGaAs/GaAs heterostructure. Semicond., 39(9), 1082–1086.
Abstract: Experimental results obtained by studying the main characteristics of a millimeter-submillimeter wave mixer based on the hot-electron effect in a two-dimensional electron gas in a AlGaAs/GaAs heterostructure with a phonon-scattering cooling mechanism for charge carriers are reported. The gain bandwidth of the mixer is 4 GHz, the internal conversion losses are 13 dB, and the optimum local-oscillator power is 0.5 μW (for a mixer area of 1 μm2). It is shown that a millimeter-submillimeter-wave receiver with a noise temperature of 1900 K can be developed on the basis of a AlGaAs/GaAs mixer. This mixer also appears to be promising for use in array receiver elements.
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Maslennikov, S. N., Finkel, M. I., Antipov, S. V., Polyakov, S. L., Zhang, W., Ozhegov, R., et al. (2006). Spiral antenna coupled and directly coupled NbN HEB mixers in the frequency range from 1 to 70 THz. In Proc. 17th Int. Symp. Space Terahertz Technol. (pp. 177–179). Paris, France.
Abstract: We investigate both antenna coupled and directly coupled HEB mixers at several LO frequencies within the range of 2.5 THz to 70 THz. H20 (2.5+10.7 THz), and CO2 (30 THz) gas discharge lasers are used as the local oscillators. The noise temperature of antenna coupled mixers is measured at LO frequencies of 2.5 THz, 3.8 THz, and 30 THz. The results for both antenna coupled and directly coupled mixer types are compared. The devices with in—plane dimensions of 5x5 ,um 2 are pumped by LO radiation at 10.7 THz. The directly coupled HEB demonstrates nearly flat dependence of responsivity on frequency in the range of 25+64 THz.
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