76 research outputs found
Hanle effect in coherent backscattering
We study the shape of the coherent backscattering (CBS) cone obtained when
resonant light illuminates a thick cloud of laser-cooled rubidium atoms in
presence of a homogenous magnetic field. We observe new magnetic
field-dependent anisotropies in the CBS signal. We show that the observed
behavior is due to the modification of the atomic radiation pattern by the
magnetic field (Hanle effect in the excited state).Comment: 4 pages, 3 figure
Spin relaxation in low-dimensional systems
We review some of the newest findings on the spin dynamics of carriers and
excitons in GaAs/GaAlAs quantum wells. In intrinsic wells, where the optical
properties are dominated by excitonic effects, we show that exciton-exciton
interaction produces a breaking of the spin degeneracy in two-dimensional
semiconductors. In doped wells, the two spin components of an optically created
two-dimensional electron gas are well described by Fermi-Dirac distributions
with a common temperature but different chemical potentials. The rate of the
spin depolarization of the electron gas is found to be independent of the mean
electron kinetic energy but accelerated by thermal spreading of the carriers.Comment: 1 PDF file, 13 eps figures, Proceedings of the 1998 International
Workshop on Nanophysics and Electronics (NPE-98)- Lecce (Italy
Zero-Field Dichroism in the Solar Chromosphere
We explain the linear polarization of the Ca II infrared triplet observed
close to the edge of the solar disk. In particular, we demonstrate that the
physical origin of the enigmatic polarizations of the 866.2 nm and 854.2 nm
lines lies in the existence of atomic polarization in their metastable lower
levels, which produces differential absorption of polarization components
(dichroism). To this end, we have solved the problem of the generation and
transfer of polarized radiation by taking fully into account all the relevant
optical pumping mechanisms in multilevel atomic models. We argue that
`zero-field' dichroism may be of great diagnostic value in astrophysics.Comment: 10 pages, 3 figure
Analogue of the quantum hanle effect and polarization conversion in non-hermitian plasmonic metamaterials
This document is the Accepted Manuscript version of a Published Work that appeared in final form in
Nano Letters, copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see http://pubs.acs.org/page/policy/articlesonrequest/index.htmlThe Hanle effect, one of the first manifestations of quantum theory introducing the concept of coherent superposition between pure states, plays a key role in numerous aspects of science varying from applicative spectroscopy to fundamental astrophysical investigations. Optical analogues of quantum effects help to achieve deeper understanding of quantum phenomena and, in turn, to develop cross-disciplinary approaches to realizations of new applications in photonics. Here we show that metallic nanostructures can be designed to exhibit a plasmonic analogue of the quantum Hanle effect and the associated polarization rotation. In the original Hanle effect, time-reversal symmetry is broken by a static magnetic field. We achieve this by introducing dissipative level crossing of localized surface plasmons due to nonuniform losses, designed using a non-Hermitian formulation of quantum mechanics. Such artificial plasmonic "atoms" have been shown to exhibit strong circular birefringence and circular dichroism which depends on the value of loss or gain in the metal-dielectric nanostructure. © 2012 American Chemical Society.This work has been supported in part by EPSRC (UK). P.G. acknowledges Royal Society for a Newton International Fellowship. F.J.R.-F. acknowledges support from grant FPI of GV and the Spanish MICINN under contracts CONSOLIDER EMET CSD2008-00066 and TEC2011-28664-C02-02.Ginzburg, P.; RodrĂguez Fortuño, FJ.; MartĂnez Abietar, AJ.; Zayats, AV. (2012). Analogue of the quantum hanle effect and polarization conversion in non-hermitian plasmonic metamaterials. Nano Letters. 12(12):6309-6314. https://doi.org/10.1021/nl3034174S63096314121
Resonant nonlinear magneto-optical effects in atoms
In this article, we review the history, current status, physical mechanisms,
experimental methods, and applications of nonlinear magneto-optical effects in
atomic vapors. We begin by describing the pioneering work of Macaluso and
Corbino over a century ago on linear magneto-optical effects (in which the
properties of the medium do not depend on the light power) in the vicinity of
atomic resonances, and contrast these effects with various nonlinear
magneto-optical phenomena that have been studied both theoretically and
experimentally since the late 1960s. In recent years, the field of nonlinear
magneto-optics has experienced a revival of interest that has led to a number
of developments, including the observation of ultra-narrow (1-Hz)
magneto-optical resonances, applications in sensitive magnetometry, nonlinear
magneto-optical tomography, and the possibility of a search for parity- and
time-reversal-invariance violation in atoms.Comment: 51 pages, 23 figures, to appear in Rev. Mod. Phys. in Oct. 2002,
Figure added, typos corrected, text edited for clarit
Spintronics: Fundamentals and applications
Spintronics, or spin electronics, involves the study of active control and
manipulation of spin degrees of freedom in solid-state systems. This article
reviews the current status of this subject, including both recent advances and
well-established results. The primary focus is on the basic physical principles
underlying the generation of carrier spin polarization, spin dynamics, and
spin-polarized transport in semiconductors and metals. Spin transport differs
from charge transport in that spin is a nonconserved quantity in solids due to
spin-orbit and hyperfine coupling. The authors discuss in detail spin
decoherence mechanisms in metals and semiconductors. Various theories of spin
injection and spin-polarized transport are applied to hybrid structures
relevant to spin-based devices and fundamental studies of materials properties.
Experimental work is reviewed with the emphasis on projected applications, in
which external electric and magnetic fields and illumination by light will be
used to control spin and charge dynamics to create new functionalities not
feasible or ineffective with conventional electronics.Comment: invited review, 36 figures, 900+ references; minor stylistic changes
from the published versio
Selective Absorption Processes as the Origin of Puzzling Spectral Line Polarization from the Sun
Magnetic fields play a key role in most astrophysical systems, from the Sun
to active galactic nuclei. They can be studied through their effects on atomic
energy levels, which produce polarized spectral lines. In particular,
anisotropic radiation pumping processes (which send electrons to higher atomic
levels) induce population imbalances that are modified by weak magnetic fields.
Here we report peculiarly polarized light in the He I 10830-\AA multiplet
observed in a coronal filament located at the centre of the solar disk. We show
that the polarized light arises from selective absorption from the ground level
of the triplet system of helium, and that it implies the presence of magnetic
fields of the order of a few gauss that are highly inclined with respect to the
solar radius vector. This disproves the common belief that population
imbalances in long-lived atomic levels are insignificant in the presence of
inclined fields with strengths in the gauss range, and demonstrates the
operation of the ground-level Hanle effect in an astrophysical plasma.Comment: 22 pages and 4 figure
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