Bulletin of the Russian Academy of Sciences: Physics最新文献

The authors study the effect detuning between the group velocities of two optical harmonics has on the reflection and transmission of radiation in a layered active quadratically nonlinear medium. The reflectance and transmittance at the fundamental and doubled frequencies are determined via numerical modeling. The soliton nature of energy transfer inside a medium is demonstrated.

It is shown that a scanning probe microscope allows precise manipulation of an ensemble of upconversion nanoparticles deposited uncontrollably on the surface of a glass substrate. The possibility of controlled movement of such particles over distances of several tens of micrometers is demonstrated, leaving several upconversion nanoparticles separated from others (or small conglomerates of them) on a surface with an area of ∼10⁴ μm². The system of marks on the substrate makes it easy to find such particles and perform a series of manipulations, including movements over submicrometer distances and rotation at a given angle of a single upconversion nanoparticle. The force of an individual upconversion nanoparticle’s adhesion to the surface of a substrate is estimated.

The authors consider using upconversion fluoride nanoparticles of NaYF₄ doped with Yb³⁺ and Er³⁺ ions as ordered non-invasive hidden labels. At the first stage the synthesized upconversion fluoride nanoparticles have been deposited from the suspension onto the substrate with mechanical scratches used as large-scale markers. The scanning probe microscope is then used to move individual upconversion nanoparticles macroscopically significant distances and deposit them in a controlled manner onto a clean surface, thereby imprinting nanoobjects. The displacement and deposition process has been monitored using a conventional optical microscope. Luminescent signals from regularly placed labels have been recorded in an optical confocal microscope.

Experimental results are presented on the formation of ordered structures of latex microparticles with diameters of 3 and 5 μm using arrays of point optothermal traps. The working area of the phase mask is divided into sub-elements to obtain the traps. A specific distribution of the phase delay of the prism (wedge) is specified for each trap.

Crystals of the narrow-band semiconductor Pb_{1 – x – y}Gd_xCu_yS (x = 1.1 × 10^–3, y = 2.5 × 10^–3) at temperatures T = 5–300 K demonstrated unusual dependences of the shape of the lines of the electron paramagnetic resonance (EPR) spectra of paramagnetic centers of Gd³⁺ on temperature and microwave power in the resonator of EPR spectrometer. Analysis of the shape parameters of the resonance lines recorded in the X band showed that one of the causes of the unusual changes in the observed EPR spectra of Gd³⁺ centers is a nonuniform distribution of the acceptor impurity of copper with the formation of regions with different concentrations of free charge carriers. Apparently, in these regions, resonance transitions between the spin states of Gd³⁺ centers differently affect the kinetic characteristics of free charge carriers, which lead to different contributions to the quasi-resonant absorption of microwave power.

The problems of synthesis of various allotropic forms of carbon under a laser impact on a carbon-containing target under the conditions of nonequilibrium phase transitions have been considered. The results of studies of the processes of controlled design of certain topological configurations of metal-carbon and diamond-like compounds in a laser experiment with laser ablation and by modeling the 1D–3D structures with a modifyable fractal dimension have been presented. The measurements of the optical and electrophysical characteristics of such structures have been discussed in terms of the possibility of controlling their functional properties.

Impurity paramagnetic complexes [NiF₄F₄F_int]^6–(C_4v), stable associates of the trivalent nickel ion with the interstitial fluorine ion ({text{F}}_{{{text{int}}}}^{-}), were synthesized in BaF₂ ionic crystals with the fluorite structure. The molecular structure of the synthesized complexes was studied by electron paramagnetic resonance at frequencies of 9.39 and 34.25 GHz in the temperature range from 5 to 250 K. It was shown that, in the studied complex, the Ni³⁺ ion (3d⁷, ⁴F, S = 3/2) replaces the lattice cation Ba²⁺ but, under the influence of ({text{F}}_{{{text{int}}}}^{-}) in the neighboring interstice of the octahedral type, is shifted toward it from the center of the coordination cube occupied by it. Under the influence of the crystal field of tetragonal symmetry, the electron spin levels of the complex are split into two Kramers doublets, of which the ground state Kramers doublet turned out to be (left| { pm 1.2} rightrangle ). The energy interval between doublets is approximately 114 GHz. The EPR spectra exhibit a superhyperfine structure caused by the interactions of the electron spin moment of the nickel ion with the nuclei of nine ligand fluorine ions. The parameters of these interactions were determined.

Numerical modeling is used to show the possibility of forming (2D + 1) short-period (3‒5 oscillations under the envelope) light bullets in noncentrosymmetric media at the second harmonic generation with phase and group velocity detunings. Only up to certain intensities does cubic nonlinearity prevent the formation of space-time solitons.

The temperature dependences of the magnetization of La_{1 – x}Sr_xFeO_{3 – δ} samples (x = 0.33, 0.50, and 0.67) have been studied. Their Neel temperatures T_N have been determined, at which non-collinear antiferromagnetism (weak ferromagnetism) is settled down in the samples. The introduction of a substituting impurity of strontium into La_{1 – x}Sr_xFeO_{3 – δ} and an increase in its content results in a considerable decrease in T_N. This effect can be compensated using vacuum heat treatment, upon which, on the contrary, a noticeable increase in T_N is observed.

Single-crystal (001) rutile plate was irradiated intensively with 40 keV argon ions. Then, electromigration of oxygen vacancies was done in the irradiated rutile. The effect the concentration and charge state of oxygen vacancies has on the color, optical absorption spectra, and photoluminescence of rutile is shown.