70 research outputs found
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
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 is much larger than the scattering
mean free path , 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
, in contrast with the generally
accepted law, derived within the diffusion approximation.Comment: 53 pages TEX, including 2 tables. The 4 figures are sent at reques
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
Unified Green’s function retrieval by cross-correlation; connection with energy principles
Interaction of particles in the near field and opposition effects in regolith-like surfaces
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