12,562 research outputs found
Experimental study of laser detected magnetic resonance based on atomic alignment
We present an experimental study of the spectra produced by
optical/radio-frequency double resonance in which resonant linearly polarized
laser light is used in the optical pumping and detection processes. We show
that the experimental spectra obtained for cesium are in excellent agreement
with a very general theoretical model developed in our group and we investigate
the limitations of this model. Finally, the results are discussed in view of
their use in the study of relaxation processes in aligned alkali vapors.Comment: 8 pages, 9 figures. Submitted to Phys. Rev. A. Related to
physics/060523
Spin noise of itinerant fermions
We develop a theory of spin noise spectroscopy of itinerant, noninteracting,
spin-carrying fermions in different regimes of temperature and disorder. We use
kinetic equations for the density matrix in spin variables. We find a general
result with a clear physical interpretation, and discuss its dependence on
temperature, the size of the system, and applied magnetic field. We consider
two classes of experimental probes: 1. electron-spin-resonance (ESR)-type
measurements, in which the probe response to a uniform magnetization increases
linearly with the volume sampled, and 2. optical Kerr/Faraday rotation-type
measurements, in which the probe response to a uniform magnetization increases
linearly with the length of the light propagation in the sample, but is
independent of the cross section of the light beam. Our theory provides a
framework for interpreting recent experiments on atomic gases and conduction
electrons in semiconductors and provides a baseline for identifying the effects
of interactions on spin noise spectroscopy
Chasing 'Slow Light'
A critical review of experimental studies of the so-called 'slow light'
arising due to anomalously high steepness of the refractive index dispersion
under conditions of electromagnetically induced transparency or coherent
population oscillations is presented. It is shown that a considerable amount of
experimental evidence for observation of the 'slow light' is not related to the
low group velocity of light and can be easily interpreted in terms of a
standard model of interaction of light with a saturable absorber.Comment: 17 pages, 8 figures, to be published in June issue of Phisics:
Uspekhi under the title "Notes on Slow Light
Nonlinear phase shift from photon-photon scattering in vacuum
We show that QED nonlinear effects imply a phase correction to the linear
evolution of electromagnetic waves in vacuum. We provide explicit solutions of
the modified Maxwell's equations for the propagation of a superposition of two
plane waves, and calculate analytically and numerically the corresponding phase
shift. This provides a new framework for the search of all-optical signatures
of photon-photon scattering in vacuum. In particular, we propose an experiment
for measuring the phase shift in projected high-power laser facilities.Comment: 4 pages, 1 figure. Some references were added, and the comparison
with AC Kerr effect has been improve
Large spin relaxation rates in trapped submerged-shell atoms
Spin relaxation due to atom-atom collisions is measured for magnetically
trapped erbium and thulium atoms at a temperature near 500 mK. The rate
constants for Er-Er and Tm-Tm collisions are 3.0 times 10^-10 cm^3 s^-1 and 1.1
times 10^-10 cm^3 s^-1, respectively, 2-3 orders of magnitude larger than those
observed for highly magnetic S-state atoms. This is strong evidence for an
additional, dominant, spin relaxation mechanism, electrostatic anisotropy, in
collisions between these "submerged-shell" L > 0 atoms. These large spin
relaxation rates imply that evaporative cooling of these atoms in a magnetic
trap will be highly inefficient.Comment: 10 pages, 3 figure
A quantitative study of spin noise spectroscopy in a classical gas of K atoms
We present a general derivation of the electron spin noise power spectrum in
alkali gases as measured by optical Faraday rotation, which applies to both
classical gases at high temperatures as well as ultracold quantum gases. We
show that the spin-noise power spectrum is determined by an electron spin-spin
correlation function, and we find that measurements of the spin-noise power
spectra for a classical gas of K atoms are in good agreement with the
predicted values. Experimental and theoretical spin noise spectra are directly
and quantitatively compared in both longitudinal and transverse magnetic fields
up to the high magnetic field regime (where Zeeman energies exceed the
intrinsic hyperfine energy splitting of the K ground state)
Detecting photon-photon scattering in vacuum at exawatt lasers
In a recent paper, we have shown that the QED nonlinear corrections imply a
phase correction to the linear evolution of crossing electromagnetic waves in
vacuum. Here, we provide a more complete analysis, including a full numerical
solution of the QED nonlinear wave equations for short-distance propagation in
a symmetric configuration. The excellent agreement of such a solution with the
result that we obtain using our perturbatively-motivated Variational Approach
is then used to justify an analytical approximation that can be applied in a
more general case. This allows us to find the most promising configuration for
the search of photon-photon scattering in optics experiments. In particular, we
show that our previous requirement of phase coherence between the two crossing
beams can be released. We then propose a very simple experiment that can be
performed at future exawatt laser facilities, such as ELI, by bombarding a low
power laser beam with the exawatt bump.Comment: 8 pages, 6 figure
Faraday-rotation fluctuation spectroscopy with static and oscillating magnetic fields
By Faraday-rotation fluctuation spectroscopy one measures the spin noise via
Faraday-induced fluctuations of the polarization plane of a laser transmitting
the sample. In the fist part of this paper, we present a theoretical model of
recent experiments on alkali gas vapors and semiconductors, done in the
presence of a {\em static} magnetic field. In a static field, the spin noise
shows a resonance line, revealing the Larmor frequency and the spin coherence
time of the electrons. Second, we discuss the possibility to use an {\em
oscillating} magnetic field in the Faraday setup. With an oscillating field
applied, one can observe multi-photon absorption processes in the spin noise.
Furthermore an oscillating field could also help to avoid line broadening due
to structural or chemical inhomogeneities in the sample, and thereby increase
the precision of the spin-coherence time measurement.Comment: 5 pages, 7 figure
GHz Spin Noise Spectroscopy in n-Doped Bulk GaAs
We advance spin noise spectroscopy to an ultrafast tool to resolve high
frequency spin dynamics in semiconductors. The optical non-demolition
experiment reveals the genuine origin of the inhomogeneous spin dephasing in
n-doped GaAs wafers at densities at the metal-to-insulator transition. The
measurements prove in conjunction with depth resolved spin noise measurements
that the broadening of the spin dephasing rate does not result from thermal
fluctuations or spin-phonon interaction, as previously suggested, but from
surface electron depletion
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