Effective collection of Brillouin scattered light in liquids

Devices for the collection of Brillouin scattered light in liquids are discussed. Optical systems have hitherto employed conical mirrors; their angular acceptance functions are presented. Novel devices proposed and discussed are the cylinder lens and the “scattering tube” (a cylindrical mirror). Results of applications are reported. This work was supported by the “Deutsche Forschungsgemeinschaft”.     

Optical vortices in the scattering field of magnetic domain holograms

Experimental investigations and theoretical-model analyses have been made of the magnetooptic diffraction of light at ferrite garnet magnetic films with a banded domain structure which includes isolated magnetic grating defects in the form of “forks” and “breaks.” An analysis of the magnetic grating structure and the light diffraction field shows that in terms of its action on laser radiation, a banded domain grating is similar to a computer-synthesized phase hologram of an isolated pure screw-wavefront dislocation. It is shown that as a result of magnetooptic diffraction at a magnetic hologram, optical vortices may be reconstructed with a helicoidal wavefront carrying the topological charge l=±1,±2. Zh. Tekh. Fiz. 68, 54–58 (December 1998)     

Double negative in flexural single metal layer at visible frequencies

We theoretically investigate a thin single metal layer covered on sub-wavelength dielectric grating. Numerical simulations show that the structure has negative index in the normal direction at visible frequencies. Structural investigation demonstrates that the simultaneous negative permittivity and permeability at an overlapping frequency range are attributed to the metal cut-wire and “U”-shaped structure disassembled from the structure, respectively. Furthermore, parametric exploration for practical fabrication is presented.     

Sounding of an artificially perturbed ionosphere by means of an ionosonde/position finder with chirp modulation of the signal

We describe the operation of an ionosonde/position finder with chirp modulation of the signal. The first results of measuring the characteristics of short-wave radio signals scattered by artificial small-scale inhomogeneities, which were obtained by means of an ionosonde/position finder on the IZMIRAN—“SURA”—Rostov-on-Don path are presented. It was found that under certain ionospheric conditions, the angular and frequency selection of the scattered signals take place, in which case the signals are observed simultaneously in several frequency intervals (mainly, in three, namely, 6–9.5 MHz, 10–12 MHz, and 15–18 MHz) with different angles of incidence of radio waves in the vertical plane. In this case, the incidence angles were 20◦–35◦, 18◦–32◦, and 10◦–20◦ from the horizon for the first, second, and third frequency interval, respectively. Ionograms of oblique sounding were modeled allowing for the scattering of radio waves by artificial small-scale inhomogeneities. It is shown that at frequencies from 10 to 12 MHz, aspect conditions are fulfilled for the signals ducting along the high-angle beam (Pedersen mode). At frequencies 15–18 MHz (higher than the maximum observable frequency of the forward signal on the path IZMIRAN—Rostov-on-Don), aspect scattering conditions are fulfilled for the signals incident on a scattering area in the ascending part of the trajectory. At low frequencies 6–9.5 MHz (below the maximum observed frequency of the forward signal on the IZMIRAN—Rostov-on-Don path), the observable additional signals are caused by the scattering of radio waves by artificial inhomogeneities with subsequent relfection of the scattered signal from the Earth on the “SURA”—Rostov-on-Don path. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 52, No. 4, pp. 267–278, April 2009.     

Regaining profiles of extinction coefficients of optically dense scattering media in laser location measurements

We suggest a procedure for regaining spectral values of the extinction coefficients ε(r) of optically dense scattering media in laser location measurements. Allowance is made for the contribution of multiple scattering to a recorded signal and its correction for the degree of change of the qualitative composition of the scattering medium. The procedure can increase the accuracy of regaining ε(r) and eliminate the “edge effect” at the end of the probed path. The latter is achieved by determining a calibration constant from the transparency value of the whole probing range, which is calculated from back-scattered signals corrected based on the constancy of the lidar ratio. We present an algorithm for calculating the correction coefficient. The efficiency of regaining profiles of ε(r) is estimated using the atmospheric situation of a pure atmosphere and an extended smoke cloud arising from forest fires as an example. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 4, pp. 522–527, July–August, 2007.     

Optical characteristics of a multilayer photovoltaic cell for oblique incidence of light

Taking into account the contributions of interference and incoherent multiple reflections of light in the substrate, we have determined the distribution of the absorbed energy density Q in layers of a multilayer photovoltaic cell in the general case of oblique incidence of light on the cell. The relations obtained are expressed in terms of the Fresnel reflection and transmission coefficients for interfaces between media, which for oblique incidence are different for s and p polarization of the incident light. The energy absorbed by an active layer of the cell varies very slightly with the angle of incidence if the maximum in the Q distribution is located at a heterojunction. We carried out a numerical analysis for a five-layer cell based on a copper phthalocyanine-fullerene heterojunction. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 6, pp. 795–800, November–December, 2007.     

Nuclear resonant scattering using synchrotron radiation

A one-dimensional quantum model for nuclear resonant scattering using synchrotron radiation has been developed. This model gives a clear physical interpretation of the most prominent features of the coherent forward scattering process namely, the “speed-up” and “dynamical beat” effects. The form of the solution, for the time-dependent forward scattered intensity of the resonant radiation from the resonant medium after synchrotron radiation excitation, is a finite series. This unique solution can be interpreted in terms of a summation over all multiple forward scattering paths the radiation takes in reaching the detector. The resonant medium is represented by a linear chain of N effective resonant nuclei. The analysis starts from a coupled set of quantum mechanical equations for the relevant amplitudes in frequency space. Transformation to the time domain gives an analytical expression for the forward scattered intensity. The contribution of every order of the multiple scattering processes from the N effective nuclei appears naturally. The expression gives a clear physical understanding of all relevant aspects of resonant forward nuclear scattering. Furthermore, the present formalism allows the consideration of incoherent processes. This permits the study of processes in which there is gamma emission with recoil or emission of internal-conversion electrons. This revised version was published online in August 2006 with corrections to the Cover Date.     

Analysis of Electromagnetic Waves Scattering by a Finite Size Dielectric and Metal Cylinder in a Rectangular Waveguide

The paper presents a rigorous solution of the scattering problem by a circular dielectric and perfectly conducting cylinders of any radius and any height in the rectangular waveguide oriented perpendicularly to a wall. The method is based on the representation of fields in waveguide and dielectric medium by cylindrical eigenfunctions and application of boundary conditions on surfaces of the cylinder to evaluate the fields inside and outside the cylinder. The reflection and transmission coefficients are expressed through the fields. As an example the reflection and transmission coefficients versus frequency for various dielectric and metallic cylinders are computed. The comparison of numerical with experimental data is presented.     

Generalized Arago–Fresnel laws: the EME-flow-line description

We study experimentally and theoretically the influence of light polarization on the interference patterns behind a diffracting grating. Different states of polarization and configurations are considered. The experiments are analyzed in terms of electromagnetic energy (EME) flow lines, which can be eventually identified with the paths followed by photons. This gives rise to a novel trajectory interpretation of the Arago–Fresnel laws for polarized light, which we compare with interpretations based on the concept of “which-way” (or “which-slit”) information.     

Properties of Near and Far Fields for the Electric Line Source Illumination of a Lossy Metamaterial Covered Dielectric Cylinder

The electric field properties of the electric line source radiation in the presence of a lossy metamaterial covered dielectric cylinder are investigated. Firstly, the electromagnetic model configuration is given. The exact solution of the electromagnetic is presented. Secondly, the near field and the far field properties are investigated according to the electromagnetic and geometrical parameters. The different “focus” phenomenon, the directivities and the normalized radiation resistance are discussed and important conclusions are obtained. During all the numerical computation, the lossy conventional material covered dielectric cylinder is utilized as the reference.     

Atom as a “dressed” nucleus

We show that the electrostatic potential of an atomic nucleus “seen” by a fast charged projectile at short distances is quantum mechanically smeared due to nucleus motion around the atomic center of inertia. For example, the size of the “positive charge cloud” in the Hydrogen ground state is much larger than the proper proton size. For target atoms in excited initial states, the effect is even larger. The elastic scattering at large angles is generally weaker than the Rutherford scattering since the effective potential at short distances is softer than the Colombian one due to a natural “cutoff”. In addition, the large-angle scattering leads to target atom excitations due to pushing the nucleus (⇒ inelastic processes). The Rutherford cross section is in fact inclusive rather than elastic. These results are analogous to those from QED. Non-relativistic atomic calculations are presented. The difference and the value of these calculations arise from nonperturbatively (exact) nucleus “dressing” that immediately leads to correct physical results and to significant technical simplifications. In these respects a nucleus bound in an atom is a simple but rather realistic model of a “dressed” charge in the QFT. This idea is briefly demonstrated on a real electron model (electronium) which is free from infinities.      

Soaring interfaces, vortices and vortex systems inside the internal waves wake past the horizontally moving cylinder in a continuously stratified fluid

The flow pattern around a horizontal cylinder towed at constant velocity along isopycnic plane in a continuously stratified liquid is visualized by conventional techniques of “Vertical slit-Foucault’s knife”, “Maksoutov’s slit-thread” and “horizontal slit-regular grating”. Using sensitive high-resolution methods allows detail studying such component of stratified flow structures as soaring interfaces, singular soaring vortices and vortex systems, which arise directly inside the internal waves field past the cylinder. These flow elements having high level of vorticity are separated from the downstream wake by a strip of fluid without any small-scale inhomogeneities. Formation of singular vortex dipoles on leading edges of soaring interfaces is investigated in details in a wide range of flow parameters.     

Elastic neutron scattering and dielectric behaviour of 4% brominated betaine calcium chloride dihydrate (BCCD)

We report a combined experimental study by means of elastic neutron scattering and dielectric measurements of a partially deuterated and brominated BCCD (Betaine Calcium Chloride Dihydrate) crystal. The lowest-temperature phase is one-dimensional modulated and characterized by the coexistence of different commensurate domains (with = 1/4, 4/17, 2/9 and 1/5 on cooling), but with a clear predominance of the five-fold phase. A huge global thermal hysteresis of the wave-vector of the modulation, attaining values of about 9 K in the incommensurate phase and up to 15 K in the “harmless” low temperature part of the phase diagram, is observed up to . The role of lattice defects on this phenomenon is discussed. Similarly to the behaviour of the pure compound, the structural modulation evolves on cooling towards a soliton regime (growth of third and fifth-order satellite peaks), probably with respect to a non-stabilized non-modulated ferroelectric phase. The critical temperatures deduced from dielectric constant and pyroelectric current measurements are in very good agreement with those obtained from neutron scattering. The dielectric anomaly observed in at K, and known as the “-anomaly”, could not be related with any special feature detected in the neutron data, and in particular no correlation between this anomaly and the appearance of the soliton regime can be established. Received 26 October 1998     

Observation of phase-matched electromagnetic scattering in an active dielectric cylinder

A theoretical investigation of oblique plane-wave electromagnetic scattering in an active dielectric cylinder predicted the existence of anomalous resonances at discrete plane-wave angles of incidence. These resonances may be understood as being due to a leaky-wave phase-matching boundary condition. Experiments were performed with active dielectric cylinders to confirm the existence of discrete resonances. Cross coupling between TE and TM modes was clearly detected for both active and passive scattering. Enhancement of active scattered field intensities was observed in experiments with finite-diameter pump and probe laser beams. Optical pumping of a dye solution was used to provide the gain.     

Modeling of arbitrary cross-sectional cylinder using N circular cylinders for the scattering calculations

Exact solution of the electromagnetic wave scattering by N dielectric cylinders is presented by using matrix formulation. To check this present method, two comparisons between exact solutions for a single circular conducting and dielectric cylinder and this model composed of N=25 circular cylinders are made. Numerical results of conducting and dielectric square cylinder has been also checked with well-known result (B.E.M). The scattering patterns and the near field distributions in space are presented for the concave, convex and dielectric circular cylinder with conducting reflector.     

Anisotropic surface relief diffraction gratings under arbitrary plane wave incidence

A modal method is used for the analysis under oblique incidence of a diffraction grating made of anisotropic material. The problem is studied viewing the structure as the cascade of junctions between periodic arrays of anisotropic slab waveguides with the same period and different heights. This diffraction problem is formulated in terms of an integral equation that enforces the continuity of the transverse magnetic field at the junction. The unknown is the transverse electric field at the junction. It is possible to use also another formulation, where the role of the two fields is exchanged. The kernels of these equations are the relevant Green's functions, which are expressed in terms of eigenfunction expansions. The determination of the modes of the various regions composed of arrays of anisotropic dielectric slabs has been carried out by the method of spectral elements, whereby the field components are represented in a polynomial basis and the original differential eigenvalue problem is converted into an algebraic one. The integral equation is solved numerically by the method of moments and each junction is characterized by its generalized scattering matrix (GSM). Finally, the diffraction efficiencies of the grating are obtained by combining the various GSM's.     

Time-delay of classical and quantum scattering processes: a conceptual overview and a general definition

We present a step by step introduction to the notion of time-delay in classical and quantum mechanics, with the aim of clarifying its foundation at a conceptual level. In doing so, we motivate the introduction of the concepts of “fuzzy” and “free-flight” sojourn times that we use to provide the most general possible definition for the quantum time-delay, valid for simple and multichannel scattering systems, with or without conditions on the observation of the scattering particle, and for incoming wave packets whose energy can be smeared out or sharply peaked (fixed energy). We conclude our conceptual analysis by presenting what we think is the right interpretation of the concepts of sojourn and delay times in quantum mechanics, explaining why, in ultimate analysis, they should not be called “times.”     

Kinetics and Optical Properties of the Strongly Driven Gas Medium of Interacting Atoms

This paper investigates stimulated emission and absorption near resonance for a driven system of interacting two-level atoms. Microscopic kinetic equations for the density matrix elements of N-atom states including atomic motion are built, taking into account atom-field and atom-atom interactions. Analytical solutions are given for the resulting macroscopic equations in different limits, for a system composed of a strong coherent “pump” field and a weak counter-propagating “probe” field. It was shown that the existence of a dipole-dipole (long-range) interaction between atoms separated by distance less than the pump wave-length can cause the formation of periodic polarization and population structures (gratings in time and space) in the pumped medium without a probe field. The magnitude of pump induced population grating can have a strong dependence on the relation between the pump field detuning and the polarization decay rate. The “interaction” between pump and probe induced polarization/population gratings through a dipole-dipole interaction mechanism causes the absorption line shape asymmetry. Under certain conditions, this asymmetry is revealed in increasing probe gain for the “red”-shifted (relative to pump) probe and suppressing the gain for the “blue”-shifted probe field when pump is “red”-shifted relative to the ensemble averaged resonant frequency. The theoretical results are consistent with experimental data for the probe gain or absorption as the function of frequency and the dependance of the gain on atomic density for sodium vapor when the pump laser is tuned near the D ₂ line. Here the dependance of gain on particle density was explained in the terms of the long-range interaction between the atoms.