Vol 126, No 1 (2019)

The protocol of dynamic decoupling using a sequence of resonance RF pulses with different shapes in a system of dipole-coupled electron/nuclear spins with inhomogeneous broadening of the resonance line has been theoretically studied. The choice of optimal RF pulse parameters for implementation of long-lived broadband quantum memory based on these spin systems is discussed.

The possibilities of forming light fields with intensity distribution in the form of two maxima rotating during propagation using a liquid-crystal modal device are analyzed. The rate of intensity distribution rotation depending on the radius of curvature of the wave incident on the modulator, as well as the energy efficiency of the formed fields, are estimated.

We analyze numerically the femtosecond filamentation of a vortex beam with the topological charge m = 1 at wavelength λ₀ = 1800 nm in fused silica under anomalous group velocity dispersion conditions. We show that, as a pulse with a fivefold excess of its power over the critical power propagates through the medium, a multifocus ring structure of radiation with a peak intensity of higher than 10¹³ W/cm² and surface energy density of about 0.2 J/cm² is formed. The self-action of the optical vortex is accompanied by the transformation of the spectral energy mainly into the Stokes region. A comparison is made with the case of a normal dispersion of the group velocity upon the self-action of a vortex beam at the wavelength of  λ₀ = 400 nm.

Specific features of the construction and recording of axially symmetric vortex fields using diffraction optical elements, which can be used for generating single-photon states with a nonzero orbital angular momentum in the process of spontaneous parametric down-conversion, are considered.

An analysis of the prospects for creating new luminescent molecular photonics materials based on mesogenic lanthanide(III) β-diketonate complexes is presented. We consider vitrified films that combine intense monochromatic luminescence, high optical quality, and complete resistance to UV radiation with the ability to change their photophysical properties (for example, the absorption band width and luminescence intensity) depending on the local structure and under external actions, such as UV radiation and temperature. The problems of control of the photophysical properties of these films and the possibility of their application as working media of high-tech luminescent materials and devices (for example, luminescent sensors of temperature, oxygen, and UV radiation, as well as light-conversion materials) are discussed.

The temperature dependences of the positions of maxima of exciton bands in the luminescence spectra of liquid crystal nanocomposites with CdSe quantum dots with sizes of 1.8 and 2.3 nm at T = 77–300 K have been analyzed. The analysis under the theoretical model taking into account the electron–phonon interaction inside quantum dots has made it possible to calculate the values of the Huang–Rhys factor and average phonon energy in nanocrystals under study.

An approach to improving the accuracy of image processing of fluorescent shimmering single quantum dots is presented. It is based on estimating the parameters of a function describing global drift using information on a sufficiently long series of images of single quantum dots. The results of processing a series of frames obtained in experiments with single CdSe/ZnS quantum dots are presented.

The results of applying two-photon femtosecond laser photopolymerization for fabrication of structures for sensitive IR sensors are reported. Two methods of sensor fabrication, a two-wave laser stereolithography and an electron-beam lithography, are compared. The possibility of applying the obtained structures for investigation of the effect of surface-enhanced IR absorption (SEIRA) with a STED-compatible oligomer pentaerythritol tetraacrylate (PETTA) as an analytical layer is demonstrated.

We have considered the resonant nonradiative energy transfer in hybrid associates of thionine dye (TH⁺) molecules and Ag₂S colloidal quantum dots (QDs) passivated with thioglycolic acid (Ag₂S/TGA) and Ag₂S QDs stabilized with gelatin (Ag₂S/Gel). Used samples of Ag₂S QDs possess luminescence, which arises by the exciton mechanism, as well as by the recombination mechanisms of holes with electrons localized at luminescence centers and of electrons with holes localized at the luminescence centers. The quenching of luminescence of Ag₂S/TGA QDs (1.8 nm) with a maximum at 630 nm and a decrease in the luminescence lifetime from 13.7 to 6.5 ns, which occurs upon association with TH⁺ molecules, have been established. On the contrary, for associates of Ag₂S/TGA QDs (5.5 nm) with TH⁺ molecules, we have observed the quenching of luminescence of the dye and a decrease in the lifetime of this luminescence from 0.43 to 0.3 ns, as well as an enhancement of luminescence of QDs. In the case of hybrid association with TH⁺ molecules, the luminescence enhancement of Ag₂S/Gel QDs (1.6 nm) has been established, which results from the recombination of free holes with electrons localized at luminescence centers. Based on our analysis of the luminescence kinetics of the dye, we have inferred the occurrence of resonant nonradiative energy transfer from TH⁺ molecules to centers of recombination luminescence in Ag₂S/TGA (5.5 nm) and in Ag₂S/Gel (1.6 nm) QDs with its maxima at 950 and 1205 nm, respectively. For Ag₂S/TGA QDs (2.2 nm), which luminesce with a maximum at 620 nm by the exciton mechanism, we have observed a significant overlap both between the luminescence spectra of QDs and TH⁺ and between their absorption spectra. Close parameters of the luminescence kinetics for both the initial components and their associates indicate the energy transfer, which is realized in opposite directions.

We discuss particular features of generation of surface plasmon polaritons in a metal–dielectric planar interface that is coupled to semiconductor quantum dots by near-field interactions. As a model of working medium for performing numerical experiment, we use a gold metal surface onto which a polyethylene terephthalate film containing CdSe semiconductor spherical quantum dot is deposited. The problem of optimizing the radius of a quantum dot and its distance to a metal surface is solved for achieving the maximum transfer efficiency of the quantum dot energy for the generation of surface plasmon polaritons. Dispersion effects of the surface wave generation rate associated with deviations of the radius of quantum dots and their distance to the metal surface from the corresponding average values are taken into account.

We propose a method for obtaining a fluorescence tomographic image for visualization and diagnosis of tissues of a living organism. The method is based on the excitation of the luminescence of multicolor upconverting nanoparticles localized in the depth of the biological tissue or a phantom imitating it by IR light. By recording the changes in the shape of the spectrum of the intensity of luminescence radiation from luminescent nanoparticles on the surface of the tissue, it is possible to obtain information about the depth of their occurrence. To implement this approach, upconverting nanoparticles were synthesized on the base of β-NaYF₄ crystal matrix doped with rare-earth elements Yb³⁺, Er³⁺, and Tm³⁺. The luminescence spectra of the produced nanoparticles upon excitation at a wavelength of 980 nm contain three narrow bands with maxima at wavelengths 540, 655, and 800 nm.

In this paper, we combined a photoinduced electron donor—an improved green fluorescent protein (EGFP)—and protein oxidants within the same chimeric polypeptide chain. Comparison of the photostability of EGFP and chimeric proteins both in the absence and in the presence of non-protein-bound oxidants in solution showed the efficiency of the created model electron transport chains.