Field transformation in a multimode optical waveguide with random irregularities of the film surface

A self-consistent mathematical model for the transformation of the average intensity of the mode spectrum I(z) of a waveguide field in a multimode planar optical waveguide with a step profile and rough surface is developed. This model is based on the matrix model for multiple scattering of modes in an optical waveguide. The elements of the intermode scattering matrix are found, which describe the process of mutual transfer of the energy of modes along a waveguide and their transformation into radiation modes. The transformation of the I(z) modes in waveguides with large-and small-scale inhomogeneities is investigated. It is shown that the largest qualitative differences in the noted dependences manifest themselves only in the initial portions of the optical waveguide. The length z of these portions is much smaller than the characteristic scale length L _k at which the fundamental energy of the kth mode excited in the optical waveguide is renewed. The effect of self-filtration of the mode spectrum I(z) is described, as a result of which a stable (normalized), independent of distance z, distribution I* is formed. It is established that irregularities of the optical waveguide boundaries exert a depolarizing effect on a guided light beam. The specific features of the normalization of the radiative dissipation of a group of modes I_i(z) in an optical waveguide are investigated. It is ascertained that, in the case of small-scale irregularities, the attenuation coefficient is described by a nonlinear monotonic dependence α(z), which asymptotically converges to the value α*, characteristic of the normalized field I*. When the optical-waveguide film has large irregularities, the dependence α(z) is characterized by a pronounced maximum due to the formation of alternative channels of radiative dissipation of the energy of waveguide modes.     

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.     

Dissipation of ripplon flow at the surface of superfluid <Superscript>4</Superscript>He

Within the framework of quantum hydrodynamics of a superfluid helium surface, the momentum relaxation rate caused by the annihilation of two ripplons with phonon creation, inelastic phonon scattering with ripplon annihilation, and in the case of helium films one-particle ripplon scattering from the surface-level inhomogeneities introduced by the substrate roughness (new relaxation mechanism) was obtained for a ripplon gas at T?0.25 K. The contribution from the inelastic phonon scattering is negligible at these temperatures. For a film at T≤0.15 K, one-particle scattering dominates, leading to a temperature dependence of the form K∝T^5/3 for the convective thermal conductance.At higher temperatures, phonon creation with annihilation of two ripplons is the dominant mechanism, giving K∝T^?3. These results are in quantitative agreement with the available experimental data.     

Elastic Deuteron Scattering on the <Superscript>12</Superscript>C Nucleus within a Three-Body Model

The formalism developed earlier for elastic pd scattering on the basis of Glauber theory with allowance for a total spin dependence is modified by replacing pN amplitudes by amplitudes for N¹²C scattering and is applied to elastic deuteron scattering on the ¹²C nucleus. The amplitudes for elastic N¹²C scattering are obtained within the optical model. Respective numerical calculations performed at the kinetic deuteron-beam energy of 270 MeV lead to results that agree well with data on the differential cross section for d¹²C scattering into the forward hemisphere, but the calculated spin observable A _y ^d agrees with experimental data only qualitatively.     

Determination of the scattering coefficient of biological tissue considering the wavelength and absorption dependence of the anisotropy factor

The anisotropy factor g, one of the optical properties of biological tissues, has a strong influence on the calculation of the scattering coefficient μ _s in inverse Monte Carlo (iMC) simulations. It has been reported that g has the wavelength and absorption dependence; however, few attempts have been made to calculate μ _s using g values by taking the wavelength and absorption dependence into account. In this study, the angular distributions of scattered light for biological tissue phantoms containing hemoglobin as a light absorber were measured by a goniometric optical setup at strongly (405 nm) and weakly (664 nm) absorbing wavelengths to obtain g. Subsequently, the optical properties were calculated with the measured values of g by integrating sphere measurements and an iMC simulation, and compared with the results obtained with a conventional g value of 0.9. The μ _s values with measured g were overestimated at the strongly absorbing wavelength, but underestimated at the weakly absorbing wavelength if 0.9 was used in the iMC simulation.     

Absorptionsquerschnitte und Transmissionskoeffizienten für Protonen und Neutronen nach dem optischen Modell

T _l -values and absorption cross sections for protons and neutrons are calculated with optical potentials, which have been fitted to experimental scattering data. Values are given forZ=10, 20, 30, 50, 70, 90, and energies between 0.1 und 25 MeV. For protons we used the local optical potential ofPerey and for neutrons the nonlocal optical potential ofPerey andBuck. The results are compared with those of other optical potentials. In addition it is shown, that the spin-orbit-interaction leads toT _{l j} -values which sometimes differ appreciably depending whetherj equalsl+1/2 orl?1/2.     

Waves in a superlattice with anisotropic inhomogeneities

Dependences of the dispersion laws and damping of waves in an initially sinusoidal superlattice on inhomogeneities with anisotropic correlation properties are studied for the first time. The period of the superlattice is modulated by the random function described by the anisotropic correlation function K_?(r) that has different correlation radii, k _∥ ^?1 and k _⊥ ^?1 , along the axis of the superlattice z and in the plane xy, respectively. The anisotropy of the correlation is characterized by the parameter λ=1?k_⊥/k_∥ that can change from λ=0 to λ=1 when the correlation wave number k⊥ changes from k_⊥=k_∥ (isotropic 3D inhomogeneities) to k_⊥=0 (1D inhomogeneities). The correlation function of the superlattice K(r) is developed. Its decreasing part goes to the asymptote L that divides the correlation volume into two parts, characterized by finite and infinite correlation radii. The dependences of the width of the gap in the spectrum at the boundary of the Brillouin zone δν and the damping of waves ξ on the value of λ are studied. It is shown that decreasing L leads to the decrease of δν, and increase of ξ, with the increase of λ.     

Four-particle problem using Feynman diagrams

We present an exact diagrammatic approach for the problem of dimer-dimer scattering in 3D for dimers being a resonant bound state of two fermions in a spin singlet state, with corresponding scattering length a. We recover exactly the previously known result a _B = 0.60a, where a _B is the dimer-dimer scattering length. A detailed discussion of how one can “sum all the diagrams” in this case is presented. Applications to the study of 4-particle bound states of various complexes in 2D are briefly presented.     

<Emphasis Type="Italic">K</Emphasis><Superscript>±</Superscript><Emphasis Type="Italic">p</Emphasis> elastic scattering in the QCD inspired eikonalized model

Based on our previous study of the QCD inspired eikonalized model for describing vector meson photoproduction, pp, and \(\bar p\) p elastic scattering at high energies, we apply the mode to high energy K ^± p elastic scattering. The total cross section σ _tot(s), differential cross section dσ/dt, the ratio of the real part to imaginary part of the forward scattering amplitude ρ(s), and nuclear slope parameter function β(s) are calculated in the model. Our results show that the theoretical prediction for σ _tot(s) is in a good agreement with the experimental data within error bars of the data. For the other theoretical predictions there are no data to test the predictive power of the model. We need the corresponding experimental data to examinate the validity of our QCD inspired eikonalized model. However, our calculations clearly show that the Odderon exchange in the process makes a significant contribution to the observable of ρ(s) and β(s). Therefore, we may conclude that there is a good opportunity to find the QCD Odderon in the K ^± p elastic scattering at high energies.     

Optical properties of lithium niobate and lithium tantalate crystals with impurities and defects

The photoinduced and Raman scattering in lithium niobate and lithium tantalate crystals with impurities and defects have been studied. An exciting laser beam propagated either along the ferroelectric Z axis or perpendicular to it. The conditions for exciting transverse and longitudinal polar optical modes in Raman spectra are established. The regularities of the excitation of Raman spectra in several polarization geometries (X(ZZ)Y, Z(XX, Y Y)Z, Z(XX, Y Y)Z, X(ZX)Y, X(ZX)X and X(ZX)X) have been investigated. Additional (extra) spectral lines are interpreted as a manifestation of a biphonon enhanced by the Fermi resonance and the result of violation of selection rules for pseudoscalar modes of the A ₂ type due to the reduction of the point symmetry group caused by the presence of impurities and defects in real crystals. The conditions for exciting coherent longitudinal and transverse modes in lithium niobate and lithium tantalate single crystals upon stimulated Raman scattering are analyzed. The temperature evolution of the spectra recorded in the X(ZZ)Y geometry near the ferroelectric phase transition point is explained based on the concept of effective soft mode and analysis of the isofrequency opalescence effect. Strong photoluminescence is found in copper-doped lithium niobate crystals.     

Structural investigation on gamma-irradiated polyacrylamide hydrogels using small-angle neutron scattering and ultraviolet–visible spectroscopy

Small-angle neutron scattering (SANS) and ultraviolet (UV)–visible spectroscopic techniques are used to investigate the microstructural changes in polyacrylamide (PAAm) hydrogels on gamma irradiation. SANS measurements have revealed the presence of inhomogeneities in nanometre scale and reduction of their size with increase in dose. Analysis of SANS data also revealed the increase in the correlation length with increase in dose. The extinction coefficient obtained from the UV–visible spectroscopic studies exhibited λ^?β dependence between 500 and 700 nm and is understood to arise from the existence of scatterers (inhomogeneities) in submicron scale in PAAm hydrogels. The increase in value of exponent β with increase in dose indicates that the size of scatterers decrease with increase in dose.     

On the hole scattering anisotropy in the PbSb<Subscript>2</Subscript>Te<Subscript>4</Subscript> layered compound from data on the Nernst-Ettingshausen coefficient

Three independent components of the Nernst-Ettingshausen coefficient tensor Q _ikl are experimentally measured for an anisotropic single crystal of the p-PbSb₂Te₄ layered compound. The components Q ₁₂₃ and Q ₁₃₂ are found to be negative, whereas the component Q ₃₂₁ is positive. The experimental data on the anisotropy of the Nernst-Ettingshausen coefficient are discussed together with the available data on the thermopower, the Hall effect, and the electrical conductivity. The analysis demonstrates that the experimental data on the transport effects in p-PbSb₂Te₄ can be explained within a one-band model of the band spectrum and a mixed mechanism of hole scattering under the assumption that scattering from acoustic phonons and scattering from impurity ions are dominant in the cleavage plane and along the c ₃ trigonal axis, respectively.     

Plasmons in double quantum wells in a parallel magnetic field

Collective intraband charge-density excitations in the quasi-two-dimensional electron system of double GaAs/AlGaAs quantum wells in an external parallel magnetic field B_∥ are studied by inelastic light scattering. It has been found that the energy of the excitations under study (acoustic and optical plasmons) exhibits anisotropy depending on the mutual orientation of B_∥ and the excitation quasi-momentum k. It is shown theoretically that, in a strong parallel magnetic field, the effects associated with the finite width of the quantum wells dominate over the effects associated with interlayer tunneling and determine the anisotropy of plasmons. The experimental data are compared with a theoretical calculation.     

Spectroscopy of surface-enhanced raman scattering of a complex with charge transfer between a bis-crown-containing stilbene and a bis-ammonium-alkyl derivative of dipyridylethylene

The structure of a charge transfer complex (CTC) formed by a bis-crown-containing stilbene (1) and a dipyridylethylene derivative (2) is studied by surface-enhanced Raman scattering spectroscopy. It is found that an excess of 2 leads to the formation of a 1: 1 CTC structure ([1·2]), whereas an excess of 1 leads to the stabilization of a sandwichlike 2: 1 CTC structure ([1·2·1]). It is also revealed that 1 and diperchlorate of 1-ammoniumpropyl-4-methylpyridinium (5) form a 1: 1 CTC structure, which is much less stable. Analysis of the surface-enhanced Raman scattering data suggests that, in complete agreement with the Mulliken theory, the CTCs under study are ordinary molecular complexes in the ground state and the interaction of a molecular complex with a photon excites the former. The excitation is accompanied by a significant transfer of the electron density from the donor 1 to the acceptor 2 (5). The structural fragments of the molecules responsible for the intermolecular interaction and charge transfer are ascertained using model compounds. The charge transfer in donor-acceptor pairs occurs between the electronic systems of trisubstituted benzene and pyridine. A CTC of the [1·2] or [1·2·1] type contains two equivalent donor-acceptor pairs; however, only one of them is involved in the charge transfer.     

Disorder effect on the quantum Hall effect in thin films of three-dimensional topological insulators

We numerically study the quantum Hall effect (QHE) in three-dimensional topological insulator (3DTI) thin film in the presence of the finite Zeeman energy g and the hybridization gap Δ under a strong magnetic field and disorder. For Δ = 0 but g ≠ 0, the Hall conductivity remains to be odd-integer quanti-zed σ _xy = ν(e ²/h) , where ν = 2? + 1 with ? being an integer. In the presence of disorder, the Hall plateaus can be destroyed through the float-up of extended levels toward the band center and the higher plateaus disappear first. The two central plateaus with ν = ± 1 around the band center are strongest against disorder scattering. With the increasing of the disorder strength, Hall plateaus are destroyed faster for the system with a weaker magnetic field. If g = 0 but Δ ≠ 0, there is a splitting of the central (n = 0) Landau level, yielding a new plateau with ν = 0, in addition to the original odd-integer plateaus. In the strong-disorder regime, the QHE plateaus can be destroyed due to the float-up of extended levels toward the band center. The ν = 0 plateau around the band center is strongest against disorder scattering, which eventually disappears. For both g ≠ 0 and Δ ≠ 0, the simultaneous presence of nonzero g and Δ causes the splitting of the degenerating Landau levels, so that all integer Hall plateaus ν = ? appear. The ν = 0,1 plateaus are the most stable ones. In the strong-disorder regime, all QHE states are destroyed by disorder, and the system transits into an insulating phase.     

Spin observables in <Emphasis Type="Italic">np</Emphasis> elastic scattering in the energy range 200–600 MeV. Complete experiment

A survey of available experimental data on the measurement of spin observables in neutron-proton (np) elastic scattering in the neutron energy range 200–600 MeV is presented. Sixteen spin observables (the polarization of recoil particles P _0n00, the analyzing power A _00n0, the spin correlation parameters A _00nn , A _00ss , A _00sk , and A _00kk , the spin transfer parameters K _0nn0, K _0ss0, and K _0sk0, the depolarization parameters D _0n0n , D _0s0s , and D _0s0k , and the three-spin parameters N _0nkk , N _0skn , N _0ssn , and N _0sns for energies of 200–590 MeV and scattering angles in the center of mass system of 60°–164°) were studied in experiments using polarized neutron beams and polarized proton targets at the Paul Scherrer Institute. The results of these investigations present a complete set of precision data on np elastic scattering which, along with the complete set of data for proton-proton (pp) elastic scattering obtained earlier, provides a basis for unambiguous determination of the amplitudes of the scattering matrix for nucleon-nucleon (NN) elastic scattering for the channel with the isotopic spin I = 0 and makes it possible to describe NN interaction in a model-independent way.     

Wirkungsquerschnitte depolarisierender Stöße von angeregten Natriumatomen mit Edelgasatomen durch optisches Pumpen mitD 2-Licht

Optical pumping of sodium vapor withD ₂-light causes a rise of optical transparency if complete collision-induced mixing takes place among the sublevels of the excited² P-states. It causes a drop of optical transparency if there would be no mixing in the excited states. It causes no change of optical transparency if excited-state mixing is as strong as the condition 2T=3τ predicts,T being the mean collision time, τ the mean life time of the excited states. The latter case can be realized by certain buffer gas pressures. These pressures have been measured for the gases helium, neon, and argon. From these pressures excited state-mixing cross sections have been deduced by means of the quoted condition. Finally the so far used “uniform” mixing model has been critically revised. A more realistic model is proposed which ascribes excited-state-mixing to scattering phase shifts between the molecularσ- andπ-states into which the atomic² P-state splits during the collision. Nevertheless, the condition 2T=3τ is not seriously altered even in this refined model.     

Delbrück-Streuung von 17 MeV-Photonen

Differential cross sections have been measured for the small angle scattering ofγ-rays by iron, silver, tantalum, lead and uranium with 17 MeV photons from Li⁷ (p, γ) Be⁸ at mean four momentum transfersq of 0·5mc and 1·3mc and with 7 MeV photons from F¹⁹(p, αγ)O¹⁶ at mean four momentum transfer of 0·5mc. Under these experimental conditions only Compton, Rayleigh and possibly Delbrück scattering are of importance. Extrapolation of known theoretical results to higher energies shows, that Rayleigh and Compton scattering from bound electrons should depend only onq for small angles, smallq and fixedZ. Using this it follows, that at 17 MeV andq≈0·5mc an additional scattering process must be present, which increases with growingZ and which is negligible in the measurements at 17 MeV withq≈1·3mc and at 7 MeV withq≈0·5mc. These results are in qualitative agreement with the approximate theory for Delbrück scattering ofBethe andRohrlich, however experimental cross sections at 17 MeV andq≈0·5mc are about a factor of 1·6 lower than those predicted by this theory. This discrepancy is not unexpected, since exact calculations of Delbrück scattering amplitude fromKessler andZernik at 2·62 MeV and 6·14 MeV show even greater deviations in the same sense.     

Meson-baryon scattering with SU (3) invariant interactions

The static model invariant under SU₃ is discussed. The baryons and mesons are assigned according to the “eightfold way”, and the Low equation for the scattering matrix is derived. The scattering matric has been diagonalized for arbitrary mixing ofF- andD-type coupling and the crossing matrix has been calculated. To determine the mixing of the two couplings photoproduction cross sections have been calculated. From the comparison of theK ⁺ Λ andK ⁺ Σ0 production cross sections with experiment it follows that α=D/F=3.5. For this value of α the model predicts the 3/2 decublet resonance in very good agreement with the experimental situation.