468 research outputs found
Floquet–Liouville supermatrix approach. II. Intensity‐dependent generalized nonlinear optical susceptibilities
This is the published version, also available here: http://dx.doi.org/10.1063/1.451981We present a practical n o n p e r t u r b a t i v e method for e x a c t treatment of i n t e n s i t y‐d e p e n d e n t generalized nonlinear optical susceptibilities χ(ω) in intense polychromatic fields, valid for arbitrary laser intensities, detunings, and relaxation. By means of the many‐mode Floquet theory, the time‐dependent Liouville equation can be transformed into an equivalent t i m e‐i n d e p e n d e n t infinite‐dimensional Floquet–Liouville supermatrix (FLSM) eigenvalue problem. It is then shown that the nonlinear optical susceptibilities χ(ω) can be completely determined simply from the supereigenvalues and eigenfunctions of the Floquet–Liouvillian L̂ F . In addition to this exact FLSM approach, we have also presented higher‐order perturbative results, based on the extension of the Salwen’s nearly degenerate perturbation theory, appropriate for somewhat weaker fields and near‐resonant multiphoton processes, but beyond the conventional perturbative or rotating wave approximation (RWA). In the case of two‐level systems, for example, the implementation of Salwen’s method in the time‐independent L̂ F allows the reduction of the infinite‐dimensional FLSM into a 4×4 dimensional effective Hamiltonian, from which essential a n a l y t i c a l formulas for intensity‐dependent χ(ω) can be obtained. These methods are applied to a detailed study of intensity‐dependent spectralline shapes (such as hole burning and extra resonance peaks at the line center, and the effects of saturation, detuning, and radiative and collisional damping, etc.) and subharmonic structures in nonlinear multiple wave mixings χ[(m+1)ω1−mω2] for two‐level systems in intense linearly polarized bichromatic fields
Light-Induced Atomic Desorption for loading a Sodium Magneto-Optical Trap
We report studies of photon-stimulated desorption (PSD), also known as
light-induced atomic desorption(LIAD), of sodium atoms from a vacuum cell glass
surface used for loading a magneto-optical trap (MOT). Fluorescence detection
was used to record the trapped atom number and the desorption rate. We observed
a steep wavelength dependence of the desorption process above 2.6 eV photon
energy, a result significant for estimations of sodium vapor density in the
lunar atmosphere. Our data fit well to a simple model for the loading of the
MOT dependent only on the sodium desorption rate and residual gas density. Up
to 3.7x10^7 Na atoms were confined under ultra-high vacuum conditions, creating
promising loading conditions for a vapor cell based atomic Bose-Einstein
condensate of sodium.Comment: Sodium LIAD loaded MOT, 7 pages, 5 figures. Revised submitted
manuscript with minor corrections, new data presented, Fig.5 change
Controlling atomic vapor density in paraffin-coated cells using light-induced atomic desorption
Atomic-vapor density change due to light induced atomic desorption (LIAD) is
studied in paraffin-coated rubidium, cesium, sodium and potassium cells. In the
present experiment, low-intensity probe light is used to obtain an absorption
spectrum and measure the vapor density, while light from an argon-ion laser,
array of light emitting diodes, or discharge lamp is used for desorption.
Potassium is found to exhibit significantly weaker LIAD from paraffin compared
to Rb and Cs, and we were unable to observe LIAD with sodium. A simple LIAD
model is applied to describe the observed vapor-density dynamics, and the role
of the cell's stem is explored through the use of cells with lockable stems.
Stabilization of Cs vapor density above its equilibrium value over 25 minutes
is demonstrated. The results of this work could be used to assess the use of
LIAD for vapor-density control in magnetometers, clocks, and gyroscopes
utilizing coated cells.Comment: 10 pages, 11 figure
Some peculiarities in response on filling up the Fermi sphere by quarks
Considering quarks as the quasi-particles of the model Hamiltonian with
four-fermion interaction we study response on the process of filling up the
Fermi sphere by quarks.Comment: 11 pages, 5 figures, minor language improvemen
Experiment for Testing Special Relativity Theory
An experiment aimed at testing special relativity via a comparison of the
velocity of a non matter particle (annihilation photon) with the velocity of
the matter particle (Compton electron) produced by the second annihilation
photon from the decay Na-22(beta^+)Ne-22 is proposed.Comment: 7 pages, 1 figure, Report on the Conference of Nuclear Physics
Division of Russian Academy of Science "Physics of Fundamental Interactions",
ITEP, Moscow, November 26-30, 200
Loading a vapor cell magneto-optic trap using light-induced atom desorption
Low intensity white light was used to increase the loading rate of Rb
atoms into a vapor cell magneto-optic trap by inducing non-thermal desorption
of Rb atoms from the stainless steel walls of the vapor cell. An increased Rb
partial pressure reached a new equilibrium value in less than 10 seconds after
switching on the broadband light source. After the source was turned off, the
partial pressure returned to its previous value in times as short as 10
seconds.Comment: 7 pages, 6 figure
Spectral functions of the spinless Holstein model
An analytical approach to the one-dimensional spinless Holstein model is
proposed, which is valid at finite charge-carrier concentrations. Spectral
functions of charge carriers are computed on the basis of self-energy
calculations. A generalization of the Lang-Firsov canonical transformation
method is shown to provide an interpolation scheme between the extreme weak-
and strong-coupling cases. The transformation depends on a variationally
determined parameterthat characterizes the charge distribution across the
polaron volume. The relation between the spectral functions of polarons and
electrons, the latter corresponding to the photoemission spectrum, is derived.
Particular attention is paid to the distinction between the coherent and
incoherent parts of the spectra, and their evolution as a function of band
filling and model parameters. Results are discussed and compared with recent
numerical calculations for the many-polaron problem.Comment: 20 pages, 15 figures, final versio
Universality of the Gunn effect: self-sustained oscillations mediated by solitary waves
The Gunn effect consists of time-periodic oscillations of the current flowing
through an external purely resistive circuit mediated by solitary wave dynamics
of the electric field on an attached appropriate semiconductor. By means of a
new asymptotic analysis, it is argued that Gunn-like behavior occurs in
specific classes of model equations. As an illustration, an example related to
the constrained Cahn-Allen equation is analyzed.Comment: 4 pages,3 Post-Script figure
Nonequilibrium phenomena in high Landau levels
Developments in the physics of 2D electron systems during the last decade
have revealed a new class of nonequilibrium phenomena in the presence of a
moderately strong magnetic field. The hallmark of these phenomena is
magnetoresistance oscillations generated by the external forces that drive the
electron system out of equilibrium. The rich set of dramatic phenomena of this
kind, discovered in high mobility semiconductor nanostructures, includes, in
particular, microwave radiation-induced resistance oscillations and
zero-resistance states, as well as Hall field-induced resistance oscillations
and associated zero-differential resistance states. We review the experimental
manifestations of these phenomena and the unified theoretical framework for
describing them in terms of a quantum kinetic equation. The survey contains
also a thorough discussion of the magnetotransport properties of 2D electrons
in the linear response regime, as well as an outlook on future directions,
including related nonequilibrium phenomena in other 2D electron systems.Comment: 60 pages, 41 figure
Spectrometric method to detect exoplanets as another test to verify the invariance of the velocity of light
Hypothetical influences of variability of light velocity due to the
parameters of the source of radiation, for the results of spectral measurements
of stars to search for exoplanets are considered. Accounting accelerations of
stars relative to the barycenter of the star - a planet (the planets) was
carried out. The dependence of the velocity of light from the barycentric
radial velocity and barycentric radial acceleration component of the star
should lead to a substantial increase (up to degree of magnitude) semi-major
axes of orbits detected candidate to extrasolar planets. Consequently, the
correct comparison of the results of spectral method with results of other
well-known modern methods of detecting extrasolar planets can regard the
results obtained in this paper as a reliable test for testing the invariance of
the velocity of light.Comment: 11 pages, 5 figure
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