Mechanisms of ionization of <Emphasis Type="Italic">F</Emphasis><Subscript>2</Subscript>-centers in laser media on the basis of LiF crystals

F₂ color centers with a superhigh concentration (5000-cm^–1 absorption coefficient at 450 nm) were formed by high-density electron beams in a layer of LiF crystals of micrometer thickness. The F₂-centers excited by high-power nanosecond wide-band optical pulses (the “soft” pumping regime) efficiently amplified the laser radiation and showed high stability under these conditions. A low stability of F₂-centers to laser radiation (the “hard” excitation regime) is explained by the dissociation of (F ₂ ⁺ , F^–) pairs induced by two-step ionization of F₂-centers: (2hν > 4.5 eV) → F₂ → (F₂)* → F ₂ ⁺ + e; F + e → F^–; F ₂ ⁺ + F^– → 3F.     

Effect of Zeeman Depopulation Pumping on Cycling Atomic Transitions

The results of an investigation of fluorescence signal at 6S_1/2 (F_g = 4) → 6P_3/2 (F_e = 5) transition of D₂ line of atomic Cs vapor versus the magnetic field (up to B = 90 G), directed along the linear polarization of exciting light are presented. The recorded reduction of fluorescence in the magnetic field, which is especially strong at high intensity of laser radiation, is explained by conversion of the Zeeman optical pumping (the alignment) into the depopulation pumping under conditions, when the Zeeman frequency shift of individual transitions between magnetic sublevels exceeds the homogeneous width of transition. In consequence, the cycling hyperfine transition F_g = 4 → F_e = 5 is transformed into an open one.     

Self-referencing measurement of an ultrashort pulse by the standard shear interferometry method

A new method for the self-referencing measurement of the amplitude-phase shape of an ultrashort pulse is proposed. The method uses a two-frequency characteristic of the pulse, which is defined as S(F ₁)S(F ₂), where F is the frequency, S(F) is the complex Fourier spectrum of the pulse, and F ₁ and F ₂ are two independent variables. It is shown that this characteristic can be generated as a two-dimensional polychromatic light wave upon generation of the sum frequency of two crossed spectral decompositions of one and the same pulse, as well as upon space-time Fourier transform of radiation of the noncollinearly generated second harmonic of the pulse. In an orthogonal system of transverse coordinates F ₁ + F ₂ and F ₁ ? F ₂, at any given value of F ₁ + F ₂, the radiation frequency of this wave in the direction of the second coordinate F ₁ ? F ₂ does not change. Therefore, the phase structure of the two-frequency characteristic can be reconstructed by the standard method of lateral shear interferometry in the direction of this coordinate. In the reconstructed two-dimensional phase structure of the two-frequency characteristic, any section by the plane F ₁ = const or F ₂ = const yields the phase structure of the spectrum of the pulse under study. This makes it possible to reconstruct the amplitude-phase shape of the pulse.     

Magneto-optical spectroscopy and optical detection of EPR spectra of Yb<Superscript>3+</Superscript> paramagnetic centers with cubic symmetry in single crystals <Emphasis Type="Italic">Me</Emphasis>F<Subscript>2</Subscript> (<Emphasis Type="Italic">Me</Emphasis> = Cd,Ca, Pb)

Cubic paramagnetic centers formed by Yb³⁺ impurity ions in fluorite-type crystals MeF₂ (Me = Cd, Ca, Pb) have been investigated using electron paramagnetic resonance, magnetic circular dichroism, magnetic circular polarization of luminescence, Zeeman splitting of optical absorption and luminescence lines, and optical detection of electron paramagnetic resonance. The g factors of the ²Γ₇ state in the excited multiplet ² F _5/2 of Yb³⁺ ions in Me F₂ crystals, the hyperfine interaction constant ¹⁷¹ A (¹⁷¹Yb) for the excited multiplet ² F _5/2 in the CaF₂ crystal, and the energies and symmetry properties of all energy levels of Yb³⁺ ions in MeF₂ crystals are determined. The crystal-field parameters for the crystals under investigation are calculated.     

Inflation of the early cold Universe filled with a nonlinear scalar field and a nonideal relativistic Fermi gas

We consider a possible scenario for the evolution of the early cold Universe born from a fairly large quantum fluctuation in a vacuum with a size a ₀ ? l _P (where l _P is the Planck length) and filled with both a nonlinear scalar field φ, whose potential energy density U(φ) determines the vacuum energy density λ, and a nonideal Fermi gas with short-range repulsion between particles, whose equation of state is characterized by the ratio of pressure P(n _F ) to energy density ε(n _F ) dependent on the number density of fermions n _F . As the early Universe expands, the dimensionless quantity ν(n _F ) = P(n _F )/ε(n _F ) decreases with decreasing n _F from its maximum value ν_max = 1 for n _F → ∞ to zero for n _F → 0. The interaction of the scalar and gravitational fields, which is characterized by a dimensionless constant ξ, is proportional to the scalar curvature of four-dimensional space R = κ[3P(n _F )–ε(n _F )–4λ] (where κ is Einstein’s gravitational constant), and contains terms both quadratic and linear in φ. As a result, the expanding early Universe reaches the point of first-order phase transition in a finite time interval at critical values of the scalar curvature R = R _c =–μ²/ξ and radius a _c ? a ₀. Thereafter, the early closed Universe “rolls down” from the flat inflection point of the potential U(φ) to the zero potential minimum in a finite time. The release of the total potential energy of the scalar field in the entire volume of the expanding Universe as it “rolls down” must be accompanied by the production of a large number of massive particles and antiparticles of various kinds, whose annihilation plays the role of the Big Bang. We also discuss the fundamental nature of Newton’ gravitational constant G _N .     

Laser spectroscopy of Eu<Superscript>3+</Superscript> cubic centers in the CaF<Subscript>2</Subscript> bulk single crystal

The optical transitions ⁵ D _{0, 1} → ⁷ F _J (J = 0, 1, ..., 6) of Eu³⁺ cubic centers in the CaF₂ single crystal are investigated using combined excitation and emission spectroscopy at different time delays after the excitation pulse. The energies of the Stark sublevels of the ⁷ F _J ground states are determined.     

Effect of the Lattice and Spin-Phonon Contributions on the Temperature Behavior of the Ground State Splitting of Gd<Superscript>3+</Superscript> in SrMoO<Subscript>4</Subscript>

The temperature behavior of the EPR spectra of the Gd³⁺ impurity center in single crystals of SrMoO₄ in the temperature range T = 99–375 K is studied. The analysis of the temperature dependences of the spin Hamiltonian b ₂ ⁰ (T) = b₂(F) + b₂(L) and P ₂ ⁰ (T) = P₂(F) + P₂(L) (for Gd¹⁵⁷) describing the EPR spectrum and contributing to the Gd³⁺ ground state splitting ΔE is carried out. In terms of the Newman model, the values of b₂(L) and P₂(L) depending on the thermal expansion of the static lattice are estimated; the b₂(F) and P₂(F) spin-phonon contributions determined by the lattice ion oscillations are separated. The analysis of b ₂ ⁰ (T) and P ₂ ⁰ (T) is evidence of the positive contribution of the spin-phonon interaction; the model of the local oscillations of the impurity cluster with close frequencies ω describes well the temperature behavior of b₂(F) and P₂(F).     

Study of the atom-phonon coupling model for (SC) partition function: first order phase transition for an infinite linear chain

In spin-conversion (SC) compounds containing molecules organized around an iron (II) ion the fundamental level of the ion is low spin (LS), S = 0, and its first excited one is high spin (HS), S = 2. This energy diagram is due to the ligands field interaction on 3d electrons and to the spin pairing energy. Heating the compound increases the magnetic susceptibility which corresponds to a change of populations of both levels and consequently a change of spin value of the molecules. This mechanism, called spin conversion (SC), can be accompagnied by thermal hysteresis observed by studying magnetic susceptibility or high spin fraction. In that case one considers that the (SC) takes place through a first-order phase transition due to intermolecular interactions. In the atom-phonon coupling model the molecules are considered as two-level systems, or two-level atoms, and it is assumed that the elastic force constant value of the spring which links two atoms first neighbours is depending on the electronic states of both atoms. In this study we calculate the partition function of a linear chain of N atoms (N ≤ 16) and we describe the role of phonons and that of the parameter Δ which corresponds to the distance in energy between both levels. The chain free-energy function is F _atph . We introduce for the chain a free-energy function defined by the set (F _HS , F _LS , F _barr ) and we show that F _atph tends towards the previous set when N → ∞. The previous set allows to describe a first order phase transition between a (LS) phase and a (HS) one. At the crossing point between the function F _LS and F _HS , and around this point, there is an intermediate free-energy barrier which prevents the chain to change phase which can lead to thermal hysteresis. The energy gap between the free-energy function F _atph and that defined by the set (F _HS , F _LS , F _barr ) is small. So we can expect that a nanoparticule takes for free-energy function that defined by the set and then displays a thermal hysteresis.     

Geometric resonance in the optical properties of microinhomogeneous PdMn<Subscript>x</Subscript>Fe<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript> alloys

The optical properties of PdMn_xFe_1?x ternary alloys in the homogeneous ferromagnetic (F₁, for x ～ 0) and antiferromagnetic (A, for x ～ 1) states, as well as in the microinhomogeneous state (at x=0.7), are discussed. In the x=0.7 alloy, the presence of nuclei of the low-resistivity, PdFe-type F₁ phase in the high-resistivity, PdMn-type A matrix was shown to produce a narrow maximum on the optical-conductivity σ(ω) curve at E ～ 0.1 eV, which is due to a geometric resonance associated with light scattering from phase inhomogeneities of the sample. The behavior of σ(ω) in the interband transition region is dominated by parameters of the electronic spectrum of both the A and F₁ phases.     

Charge transfer over localized states in a TlS single crystal

It is revealed that TlS single crystals exhibit a variable range hopping conduction along a normal to their natural layers at temperatures T ≤ 230 K in a dc electric field and a nonactivated hopping conduction at low temperatures in strong electric fields. Estimates are made for the density of states near the Fermi level (N _F = 2.8 × 10²⁰ eV^?1 cm^?3 and their energy spread (ΔW = 0.02 eV), the localization radius (a = 33 Å), the average jump distance in the region of activated (R _av(T) = 40 Å) and nonactivated (R _av(F) = 78 Å) hopping conduction, and also the drop in the charge carrier potential energy along the jump distance in an electric field F: eFR = 0.006 and 0.009 eV at F = 7.50 × 10³ and 1.25 × 10⁴ V/cm, respectively.     

Bestimmung des elektrischen Kernquadrupolmomentes des ungeraden stabilen Strontium-87-Kerns

In order to determine the electric quadrupole moment of Sr⁸⁷ (I= 9/2) the hyperfine structure-splitting of the 5s5p ³ P ₁-state of the SrI-spectra was investigated by optical double resonance. By detection of high frequency transitions (ΔF=±1,Δm _F=0,±1) in an external magnetic fieldH ₀≈0 one obtains the hyperfine structure separations asv _F=11/2?F=9/2=1463·149 (6) Mc/sec andv _F=9/2?F=7/2=1130·264 (6) Mc/sec. From these frequencies one calculates the magnetic hyperfine structure-splitting constantA=?260·084 (2) Mc/sec and the electric quadrupole interaction constantB=?35·658 (6) Mc/sec. B leads to an electric quadrupole moment ofQ(Sr⁸⁷)=+0·36 (3)·10^?24 cm².     

Grundzustand eines Fermi-Gases mit hard-sphere-Wechselwirkung

The decomposition of the ground state wave function of a Fermi gas interacting via hard core potentials into cluster functionsS _n leads to a systematic expansion of wave function and energy in powers of the parameterc=P _F r _c (r _c =hard core radius,P _F =Fermi momentum). For instance,S _n has the order of magnitudec ^n-λ-1, if λ=number of Fermion coordinates with distances smaller thanr _c . The first three energy terms agree with the ones given by other authors. Any occurrence of singular terms in the intermediate steps of the derivation can be avoided     

One-dimensional magnetophotonic crystals with magnetooptical double layers

One-dimensional magnetophotonic microcavity crystals with nongarnet dielectric mirrors are created and investigated. The defect layers in the magnetophotonic crystals are represented by two bismuth-substituted yttrium iron garnet Bi:YIG layers with various bismuth contents in order to achieve a high magnetooptical response of the crystals. The parameters of the magnetophotonic crystal layers are optimized by numerical solution of the Maxwell equations by the transfer matrix method to achieve high values of Faraday rotation angle Θ _F and magnetooptical Q factor. The calculated and experimental data agree well with each other. The maximum values of Θ _F =–20.6°, Q = 8.1° at a gain t = 16 are obtained for magnetophotonic crystals with m = 7 pairs of layers in Bragg mirrors, and the parameters obtained for crystals with m = 4 and t = 8.5 are Θ _F =–12.5° and Q = 14.3°. It is shown that, together with all-garnet and multimicrocavities magnetophotonic crystals, such structures have high magnetooptical characteristics.     

Quantifying Correlations via the Wigner-Yanase-Dyson Skew Information

In this paper, based on a discussion about the Wigner-Yanase-Dyson (WYD) skew information, the measure F_a,α(ρ_ab) for correlations in terms of the WYD skew information is introduced and discussed. The following conclusions are obtained. For a classical-quantum state ρ_ab, F_a,α(ρ_ab)=0 if and only if ρ_ab is a product state; F_a,α(ρ_ab) is locally unitary invariant and convex on the set of states with the fixed marginal ρ_a; F_a,α(ρ_ab) decreases under local random unitary operation on H_b; For a quantum-classical state ρ_ab, F_a,α(ρ_ab) decreases under local operation on H_b; Lastly, F_a,α(ρ_ab) is computed for the pure states and the Bell-diagonal states, respectively.     

Study of absorption spectra of Er<Superscript>3+</Superscript> in KTaO<Subscript>3</Subscript> crystals

The first results of the study of optical absorption spectra of KTaO₃: Er³⁺ crystals are presented. In the 350–660-nm region, lines are observed deriving from intraconfigurational electronic transitions from the ⁴ I _15/2 ground state to levels of the ⁴ F _9/2, ⁴ S _3/2, ² H _11/2, ⁴ F _7/2, ⁴ F _5/2(⁴ F _3/2), ² G _9/2, and ⁴ G _11/2 excited states of the Er³⁺ ions. A comprehensive study of transitions to the ⁴ F _9/2, ⁴ S _3/2, ² H _11/2, and ⁴ F _7/2 levels at 77 K is carried out. The number of lines observed for the above transitions fits the theoretically possible number for ?-? electronic transitions in Er³⁺ ions in the cubic crystal field. In the case of a differently charged substituted ion, this situation occurs only under nonlocal impurity charge compensation. The energies of the excited state levels for the transitions under study are determined.     

Analytical model of a Brownian motor with a fluctuating potential

We propose a model of a Brownian motor that performs a useful work against a load force F in an asymmetric periodic potential V(x) = V(x + 2L) that undergoes random shifts by a half period L with a frequency γ. An arbitrarily shaped potential profile is repeated with an energy shift ΔV in both half-periods L, while the periodicity of the function V(x) is ensured by its jumps at x = 0 and x = L. The boundary condition at x = 0 for the distribution function of a Brownian particle allows us to introduce a high and narrow potential barrier V₀ that blocks the reverse current and leads to high efficiency of the motor (the ratio of the useful work done against the load force F to the energy imparted to the particle through the potential shifts). Based on this model, we derived exact analytical expressions for the current J and the efficiency η. In the special case of piecewise-linear potentials, J and η were plotted against F and γ for various values of the parameters ΔV and V₀. We discuss the influence of the potential shape and fluctuation frequency on the main characteristics of the motor.     

Collisional Broadening of CO<Subscript>2</Subscript> Transition Lines 10<Superscript>0</Superscript>0–00<Superscript>0</Superscript>1 by Inert Gas Atoms at 300–700 K

The spectrum of excitation of Rydberg states of thallium atoms has been investigated using a collimated atomic beam in a two-step isotope selective laser scheme 6²P_1/2 → 6²D_3/2 → Tl** in the presence of an electric field with a strength of up to 1.5 kV/cm near the level 16F_5/2. The optical transitions 6D_3/2 → 18D_3/2 and 6D_3/2 → 16G_7/2, which were induced by an external electric field and dipole-forbidden, have been studied experimentally. The values for the scalar polarizabilities (in units сm^–1/(kV/сm)²) α₀(16F_5/2) = 3.71 ± 0.3, α₀(18D_3/2) = 11.70 ± 0.25, and α₀(16G_7/2) = 44.1 ± 0.9, which are compared with the calculated one, have been obtained. The new values of energy parameters for the states 18D_3/2 and 16G_7/2 have been determined.     

M-Zentrenbildung in röntgenbestrahlten KCl-Kristallen

The production of F- and M-centres in KCl by X-irradiation has been studied at temperatures between ?20 °C and 50 °C. The optical absorption measurements could be conducted without interrupting the X-irradiation. The results can be summarized as follows: 1. In Harshaw KCl crystals the number of F-centres created by the so-called fast coloration process was proportional to the height of the absorption band at 204 mμ prior to the irradiation. 2. The F-centres formed by the fast process did not contribute to the formation of M-centres. 3. In crystals with a strong absorption band at 204 mμ unstable M-centres were observed, which decayed rapidly after the cessation of the X-irradiation. Their concentration was found to be independent of the F-centre concentration. 4. At temperatures below 0 °C the relation between the concentration of the stable M-centres and the F-centre concentration could not any longer be represented by [M]=k ₁₂·[F₁]·[F₂]+k ₂₂·[F₂]², F₁ and F₂ referring to the F-centres created respectively by the fast and the slow coloration process. Except at very low F₂-centre concentrations however the relationship [M]=k ₀+k ₂·[F₂]² represented the experimental data at all temperatures between ?20 °C and 50 °C. At constant temperaturek ₂ varied withL, the X-ray energy absorbed per unit time and unit volume, according to 1/k ₂=a+bL+cL ². The temperature dependence ofa ^?1 b ^?1 andc ^?1 could be approximated by Boltzmann factors. The corresponding activation energies wereE _a=0.12 eV,E _b=0.53 eV,E _c=0.97 eV.     

Fluorescence induction changes in bean leaves after heat treatment

The regularities in the alterations of chlorophyll a fluorescence induction curves of bean leaves after short (15 min) heating in the range of temperatures from 24 to 45°C were determined. A dramatic decrease in the relative f luorescence quenching (F_P–F_T)/F_T, as well as the F_v/_Fm ratio, were observed after heating at temperatures above 38°C, which indicates a decrease in the photochemical activity of photosystem II. The effect of an increase in the resistance of the photosynthetic apparatus to the temperature of 43°C after preheating at 37°C was demonstrated.