Electromagnetically induced transparency and two-photon absorption in the ladder system in thin columns of atomic vapors

Experimental results of the study of processes of electromagnetically induced transparency (EIT) and two-photon absorption (TPA) are presented for the ladder Ξ-system obtained using the 5S-5P-nD, mS system of levels of the ⁸⁵Rb and ⁸⁷Rb atoms with n = 5, 26, and 27 and m = 39 and 48. To perform these studies, a high-temperature optical cell was designed with several regions with the following thicknesses L: 2 mm, 0.7 mm, and the region of 2–6 μm. The advantages of using thin cells over ordinary cells several centimeters thick are demonstrated. It is shown that the EIT resonance parameters for n = 5, 26, and 27 deteriorate insignificantly for thickness down to 700 μm. The TPA is recorded with the cell thickness decreasing down to L = 6 μm. It is shown that using the EIT and TPA processes makes it possible to measure the hyperfine and fine structures of highlying atomic levels. The influence of the cell walls is appreciable in recording the EIT resonances in the system 5S-5P-39S with L = 0.7 mm and in the system 5S-5P-48S with L = 2 mm. Possible applications of the processes studied are indicated.     

Magnetically Induced Anomalous Dichroism of Atomic Transitions of the Cesium D<Subscript>2</Subscript> Line

An alternative treatment of the well-known effect of a decrease in the Morin transition temperature in hematite with a decrease in the size of crystallites to the complete disappearance of the transition for nanoparticles smaller than 20 nm is proposed. In contrast to the standard speculative explanation of this effect in terms of the effect of surface and defectiveness of grains, we suggest that the decisive factor is an increase in the contribution of the shape anisotropy of particles with a decrease in their size, which is responsible for the spread of orientations of the axes of the resulting magnetic anisotropy with respect to the crystallographic axes. Our reasons are confirmed by a numerical analysis of Mössbauer spectra of hematite nanoparticles within the continuous model of magnetic dynamics of an ensemble of antiferromagnetic nanoparticles in the two-sublattice approximation generalized to the existence of weak ferromagnetism (Dzyaloshinskii interaction).     

Linear polymer with hydrogen bonds as a nonequilibrium system

A two-temperature nonequilibrium model of a linear polymer with possible formation of hydrogen bonds between monomers is proposed. A molecule is considered to be in an adiabatic stationary state far from equilibrium. The dependence of the mean-square distance between the chain ends on the number of monomers is calculated with the simplest approach of Flory in case T > Θ.     

Divergence of the greedy algorithm in the Faber-Schauder system on a continuum cardinality set

The paper establishes that there exist a continuum cardinality set E ₀ ? [0, 1] and a function f ₀(x) ∈ C _[0,1], such that the greedy algorithm of f ₀(x) with respect to the Faber-Schauder system converges to +∞ at all points of E ₀.     

Doppler-free satellites of resonances of electromagnetically induced transparency and absorption on the D 2 lines of alkali metals

The peculiarities of intra-Doppler structures that are observed in the atomic absorption spectrum of alkali metals with the help of two independent lasers have been studied. These structures accompany ultranarrow coherent resonances of electromagnetically induced transparency and absorption. With the D ₂ line of rubidium taken as an example, it is shown that, in the scheme of unidirectional waves, the maximum number of satellite resonances caused by optical pumping selective with respect to the atomic velocity is equal to seven, while only six resonances are observed in the traditional scheme of saturated absorption with counterpropagating waves of the same frequency. The spectral position of the resonances and their polarity depend on the frequency of the saturating radiation, while their number and relative amplitude depend also on the experimental geometry. These features are of general character and should show themselves in the absorption spectrum on the D ₂ lines of all alkali metals. An explanation of these features is given. The calculated spectral separations between the resonances are compared to the experimental ones, and their possible application is discussed.     

Two strongly contrasting Λ-systems in the <Emphasis Type="Italic">D</Emphasis> <Subscript>1</Subscript> line of <Superscript>87</Superscript>Rb in a transverse magnetic field

Four different types of spectroscopic cells that cover all possible existing versions of sealed-off cells (containing alkali atomic vapor) characterized by drastically different relaxation rates γ_rel are used to study the electromagnetically induced transparency spectra of two Λ-systems in the D₁ line of ⁸⁷Rb in the presence of transverse magnetic field. Two cw narrowband diode-lasers are used to form the coupling laser radiation (with a fixed frequency) and the probe radiation with a tunable frequency. Two strongly contrasting Λ-systems are found: the first shows resonances that are transformed from dark resonances to bright resonances in all cases apart from nanocells, whereas the second shows four dark resonances in all four different types of cell. The theoretical simulations are in good agreement with the experimental results.     

Near-field scanning microwave microscope application on Cu-phthalocyaninethin-film organic field-effect transistor

By the standard vacuum evaporation technique Cu(II)-phthalocyanine (Cu-Pc) thin films have been fabricated. For the samples, prepared at room temperature and post-annealed from 100°C to 350°C temperatures, optical spectra in the visible and near IR ranges have been measured. By using nondestructive near-field scanning microwave microscopy organic field-effect transistor (OFET) based on Cuphthalocyanine thin films have been investigated. The changes of crystal structure of Cuphthalocyanine thin film from the α- to the β-phase were controlled by the temperature of annealing. The values of holes’ mobility and the electroconductivity of Cu-phthalocyanine thin films have been obtained depending on the annealing temperature.     

Synthesis of Substituted 1,2-Dihydropyridines by the Reaction of (Ethoxymethylidene)cyanoacetic Ester and Arylamides of Acetoacetic Acid

Russian Journal of Organic Chemistry - The reaction of (ethoxymethylidene)cyanoacetic ester with arylamides of acetoacetic acid proceeds under heating in the presence of triethylamine or at room...