Virtual Singular Scattering of Electromagnetic Waves in Transformation Media Concept

If a scatterer and an observation point (receive) both approach the so-called near field zone of a source of electromagnetic waves, the scattering process becomes singular one which is mathematically attributed to the spatial singularity of the free space Green function at the origin. Starting from less well known property of left-handed material slab to transfer the singularity of the free space Green function by implementing coordinate transformation, we present a phenomenon of virtual singular scattering of electromagnetic wave on an inhomogeneity located in the volume of left – handed material slab. Virtual singular scattering means that a scatterer is situated only virtually in the near field zone of a source, being, in fact, positioned in the far field zone. Such a situation is realized if a scatterer is embedded into a flat Veselago’s lens and approaches the lens’s inner focus because a slab of Veselago medium produces virtual sources inside and behind the slab and virtual scatterer (as a source of secondary waves) from both slab sides. Considering a line-like dielectric scatterer we demonstrate that the scattering efficiency is proportional to product of singular quasistatic parts of two empty space Green functions that means a multiplicative quasistatic singularity of the Green function for a slab of inhomogeneous Veselago medium. We calculate a resonance value of the scattering amplitude in the regime similar to the known Mie resonance scattering

Brightness of a phase-conjugating mirror behind a random medium

A random-matrix theory is presented for the reflection of light by a disordered medium backed by a phase-conjugating mirror. Two regimes are distinguished, depending on the relative magnitude of the inverse dwell time of a photon in the disordered medium and the frequency shift acquired at the mirror. The qualitatively different dependence of the reflectance on the degree of disorder in the two regimes suggests a distinctive experimental test for cancellation of phase shifts in a random medium.Comment: 4 pages LaTeX. 2 Postscript figures include

Light transport in cold atoms: the fate of coherent backscattering in the weak localization regime

The recent observation of coherent backscattering (CBS) of light by atoms has emphasized the key role of the velocity spread and of the quantum internal structure of the atoms. Firstly, using highly resonant scatterers imposes very low temperatures of the disordered medium in order to keep the full contrast of the CBS interference. This criterion is usually achieved with standard laser cooling techniques. Secondly, a non trivial internal atomic structure leads to a dramatic decrease of the CBS contrast. Experiments with Rubidium atoms (with a non trivial internal structure) and with Strontium (with the simplest possible internal structure) show this behaviour and confirm theoretical calculations

Diffusion and Localization of Cold Atoms in 3D Optical Speckle

In this work we re-formulate and solve the self-consistent theory for localization to a Bose-Einstein condensate expanding in a 3D optical speckle. The long-range nature of the fluctuations in the potential energy, treated in the self-consistent Born approximation, make the scattering strongly velocity dependent, and its consequences for mobility edge and fraction of localized atoms have been investigated numerically.Comment: 8 pages, 11 figure

Resonant scattering in a strong magnetic field: exact density of states

We study the structure of 2D electronic states in a strong magnetic field in the presence of a large number of resonant scatterers. For an electron in the lowest Landau level, we derive the exact density of states by mapping the problem onto a zero-dimensional field-theoretical model. We demonstrate that the interplay between resonant and non-resonant scattering leads to a non-analytic energy dependence of the electron Green function. In particular, for strong resonant scattering the density of states develops a gap in a finite energy interval. The shape of the Landau level is shown to be very sensitive to the distribution of resonant scatterers.Comment: 12 pages + 3 fig

Anisotropic multiple scattering in diffuse media

The multiple scattering of scalar waves in diffusive media is investigated by means of the radiative transfer equation. This approach amounts to a resummation of the ladder diagrams of the Born series; it does not rely on the diffusion approximation. Quantitative predictions are obtained, concerning various observables pertaining to optically thick slabs, such as the mean angle-resolved reflected and transmitted intensities, and the shape of the enhanced backscattering cone. Special emphasis is put on the dependence of these quantities on the anisotropy of the cross-section of the individual scatterers, and on the internal reflections due to the optical index mismatch at the boundaries of the sample. The regime of very anisotropic scattering, where the transport mean free path $\ell^*$ is much larger than the scattering mean free path $\ell$, is studied in full detail. For the first time the relevant Schwarzschild-Milne equation is solved exactly in the absence of internal reflections, and asymptotically in the regime of a large index mismatch. An unexpected outcome concerns the angular width of the enhanced backscattering cone, which is predicted to scale as $\Delta\theta\sim\lambda/\sqrt{\ell\ell^*}$, in contrast with the generally accepted $\lambda/\ell^*$ law, derived within the diffusion approximation.Comment: 53 pages TEX, including 2 tables. The 4 figures are sent at reques

Temperature Reconstruction in Depth of Biological Object by Acoustical Radiometer

Abstract-Acoustothermometrical measurements were carried out for the model biological objects. As model objects we used the plasticine bodies placed in the water. In the experiment the model objects were being heated up and cooled down. The temporal dependences of their acoustobrightness temperatures were obtained and the reconstruction of the 2-D temperature distribution was made. The position, size and temperature of the thermal source were detected. The reconstruction error was about 1-2 mm for the position and size and about 1 K for the temperature. These results were obtained when the measurement time was about 50 s. As well we carried out the acoustothermometrical control during the laser hyperthemia of the mammary gland. The medicine procedure was continued 10 min and the maximum gland acoustobrightness temperature was increased at about 7 degrees