1,469 research outputs found

    Transverse localization and slow propagation of light

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    The effect of finite control beam on the transverse spatial profile of the slow light propagation in an electromagnetically induced transparency medium is studied. We arrive at a general criterion in terms of eigenequation, and demonstrate the existence of a set of localized, stationary transverse modes for the negative detuning of the probe signal field. Each of these diffraction-free transverse modes has its own characteristic group velocity, smaller than the conventional theoretical result without considering the transverse spatial effect

    Electromagnetically induced transparency in rubidium vapor prepared by a comb of short optical pulses

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    Journals published by the American Physical Society can be found at http://publish.aps.org/It was shown by Kocharovskaya and Khanin [Sov. Phys. JETP 63, 945 (1986)] that a comb of optical pulses can induce a ground-state atomic coherence and change the optical response of an atomic medium. In our experiment, we studied the propagation of a comb of optical pulses produced by a mode-locked diode laser in rubidium atomic vapor. Electromagnetically induced transparency (EIT) was observed when the pulse repetition rate is a subharmonic of the hyperfine splitting of the ground state. The width of the EIT resonance is determined by the relaxation rate of the ground-state coherence. Possible applications to magnetometery, atomic clocks, and frequency chains are discussed

    Enhancement of field generation via maximal atomic coherence prepared by fast adiabatic passage in Rb vapor

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    We have experimentally demonstrated the enhancement of coherent Raman scattering in Rb atomic vapor by exciting atomic coherence with fractional stimulated Raman adiabatic passage. Experimental results are in good agreement with numerical simulations. The results support the possibility of increasing the sensitivity of CARS by preparing atomic or molecular coherence using short pulses

    Why the two-pulse photon echo is not a good quantum memory protocol

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    We consider in this paper a two-pulse photon echo sequence as a potential quantum light storage protocol. It is widely believed that a two-pulse scheme should lead to very low efficiency and is then not relevant for this specific application. We show experimentally by using a Tm3+{}^{3+}:YAG crystal that such a protocol is on contrary very efficient and even too efficient to be considered as a good quantum storage protocol. Our experimental work allows us to point out on one side the real limitations of this scheme and on the other side its benefits which can be a source of inspiration to conceive more promising procedures with rare-earth ion doped crystals

    Quantum Thermodynamic Cycles and quantum heat engines

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    In order to describe quantum heat engines, here we systematically study isothermal and isochoric processes for quantum thermodynamic cycles. Based on these results the quantum versions of both the Carnot heat engine and the Otto heat engine are defined without ambiguities. We also study the properties of quantum Carnot and Otto heat engines in comparison with their classical counterparts. Relations and mappings between these two quantum heat engines are also investigated by considering their respective quantum thermodynamic processes. In addition, we discuss the role of Maxwell's demon in quantum thermodynamic cycles. We find that there is no violation of the second law, even in the existence of such a demon, when the demon is included correctly as part of the working substance of the heat engine.Comment: 17 pages, 9 figures, 4 table

    Coherent Excitation of a Two-Level Atom driven by a far off-resonant Classical Field: Analytical Solutions

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    We present an analytical treatment of coherent excitation of a Two-Level Atom driven by a far-off resonant classical field. A class of pulse envelope is obtained for which this problem is exactly solvable. The solutions are given in terms of Heun function which is a generalization of the Hypergeometric function. The degeneracy of Heun to Hypergeometric equation can give all the exactly solvable pulse shapes of Gauss Hypergeometric form, from the generalized pulse shape obtained here. We discuss the application of the results obtained to the generation of XUV.Comment: 9 Pages, 8 Figures. Accepted for Physical Review A as a regular articl

    Experimental observation of vibrations produced by pulsed laser beam in MgO:57Fe

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    We report the first observation of a laser-produced vibration with the aid of Mössbauer techniques. Thin platelets of MgO single crystals were doped by diffusion of 57Fe atoms. The illumination of the MgO: 57Fe sample with a pulsed Nd:YAG laser produced a significant broadening of the Mössbauer spectrum. In order to find out what caused these changes, we performed a series of time-domain experiments, in which the Mössbauer spectra were collected only during a 2.5 μs gate interval. This gate interval was swept from 5 μs to 190 μs over the time interval between the two laser pulses. After laser irradiation, the position of the Mössbauer line was found to be changing in time as a decaying oscillations of well-defined frequency, which can be due to the vibration of the sample induced by the laser pulse. © 2006 Springer Science+Business Media, Inc

    Suppression of γ-photon absorption via quantum interference

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    We show that the interference effects (similar to electromagnetically induced transparency, which was widely studied earlier in electronic transitions in optics) may appear in -radiation at nuclear transitions under the condition of nuclear level anticrossing. We demonstrate it also experimentally in optically thin samples of FeCO3

    Флуоресцентная диагностика с хлорином е6 в хирургии глиом низкой степени злокачественности

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    Intraoperative fluorescence diagnostics of high-grade gliomas is widely used in neurosurgical practice. This work analyzes the possibilities of fluorescence diagnostics for low-grade gliomas (LGG) using chlorin e6 photosensitizer. The study included patients with newly diagnosed LGG, for whom chlorin e6 was used for intraoperative fluorescence control at a dose of 1 mg/kg. During the operation, the fluorescence intensity of various areas of the putative tumor tissue was analyzed using the RSS Cam – Endo 1.4.313 software. Tissue samples with various degrees of fluorescence intensity were compared with the results of their histopathological analysis (WHO tumor diagnosis, Ki-67 index, P53, VEGF). Fluorescence was detected in more than half of the cases, but in most cases had a focal character and low fluorescence intensity. The fluorescence intensity directly correlated with the data of histopathological examination of tumor tissues (Ki-67 index (p=0.002), expression of P53 (p=0.0015) and VEGF (p=0.001)). The sensitivity of the method for LGG surgery was 72%, the specificity was 56,7%. Intraoperative fluorescence diagnostics with chlorin e6 can be used in LGG surgery, especially to visualize intratumoral areas with a higher degree of anaplasia.Применение интраоперационной флуоресцентной диагностики для глиом высокой степени злокачественности широко используется в нейрохирургической практике. В работе проанализированы возможности флуоресцентной диагностики для глиом низкой степени злокачественности с использованием хлорина е6. В исследование были включены пациенты с впервые диагностированной глиомой низкой степени злокачественности (low-grade glioma, LGG), у которых с целью интраоперационного флуоресцентного контроля применен препарат хлорин е6 в дозе 1 мг/кг массы тела. В процессе операции анализировали интенсивность флуоресценции различных участков предполагаемой опухолевой ткани с использованием программного обеспечения RSS Cam – Endo 1.4.313. Образцы тканей различной степени интенсивности флуоресценции сопоставляли с результатами их гистопатологического анализа (диагностика опухоли ВОЗ, индекс Ki-67, P53, VEGF). Флуоресценция выявлена в более чем половине случаев, но в большинстве случаев имела очаговый характер и низкую интенсивность флуоресценции. Интенсивность флуоресценции напрямую коррелировала с данными гистопатологического исследования тканей опухоли: индекс Ki-67 (p=0,002), экспрессия P53 (p=0,0015), VEGF (p=0,001). Чувствительность метода для хирургии LGG составила 72%, специфичность 56,7%. Проведенное исследование подтвердило, что технология интраоперационной флуоресцентной диагностики с применением хлорина е6 может применяться в хирургии LGG, особенно для визуализации внутриопухолевых участков с более высокой степенью анаплазии
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