共查询到20条相似文献,搜索用时 31 毫秒
1.
The correlation functions of the electromagnetic radiation scattered by an ensemble of atoms cooled to sub-Doppler temperatures and placed in an external static electric or magnetic field have been calculated by the diagram technique. Based on the derived relations, we have studied in detail the effect of coherent backscattering (CBS) of light. We have calculated the enhancement factor for CBS and analyzed its polarization and spectral dependences. We show that external fields affect the nature of multiple light scattering in an atomic ensemble, in particular, the character of interference upon such scattering, by leading to its optical anisotropy and related birefringence and dichroism. This, in turn, affects all of the observed CBS characteristics. 相似文献
2.
I. M. Sokolov 《Journal of Experimental and Theoretical Physics》2017,125(3):384-393
Specific features of fluorescence of dense and cold nondegenerate atomic ensembles in an external constant magnetic field are analyzed theoretically. The angular distribution, polarization properties, as well as the spectral composition of fluorescence radiation are calculated. The time variation of these characteristics after the end of the excitation pulse is analyzed. The dependence of the properties of secondary radiation on the duration and carrier frequency of the pulse is investigated. It is shown that, for dense clouds in which the free path length of quasiresonance photons is commensurate with the interatomic distance, the magnetic field significantly modifies all the observable properties of the radiation. Under these conditions, the trapping time may increase by tens of times. Magnetic field enhances the effect of quantum beats observed on time scales commensurate with the lifetime of the excited states of atoms. For individual polarization channels, this field also intensifies the phenomenon of coherent backscattering (CBS). The phenomena found are explained by the effect of magnetic field on the character of resonance dipole–dipole interaction and, as a result, on the specific features of collective phenomena in dense atomic ensembles. 相似文献
3.
We report the first observation of the dependence of the coherent-backscattering (CBS) enhanced cone with the frequency of the backscattered photon. The experiment is performed on a diffusing liquid suspension and the Doppler broadening of light is induced by the Brownian motion of the scatterers. Heterodyne detection on a CCD camera is used to measure the complex field (i.e., the hologram) of the light that is backscattered at a given frequency. The analysis of the holograms yield the frequency and the propagation direction of the backscattered photons. We observe that the angular CBS cone becomes more narrow in the tail of the Brownian spectrum. The experimental results are in good agreement with a simple theoretical model. 相似文献
4.
R. Engel A. Schiller V. G. Serbo 《The European Physical Journal C - Particles and Fields》2011,71(1):651-658
We consider coherent electromagnetic processes for colliders with short bunches, in particular the coherent bremsstrahlung (CBS). CBS is the radiation of one bunch particles in the collective field of the oncoming bunch. It can be a potential tool for optimizing collisions and for measuring beam parameters. A new simple and transparent method to calculate CBS is presented based on the equivalent photon approximation for this collective field. The results are applied to the??-factoryDA??NE. For this collider about 5·1014 d E ??/E ?? photons per second are expected in the photon energyE ?? range from the visible light up to 25 eV. 相似文献
5.
We consider coherent electromagnetic processes for colliders with short bunches, in particular the coherent bremsstrahlung (CBS). CBS is the radiation of one bunch particles in the collective field of the oncoming bunch. It can be a potential tool for optimizing collisions and for measuring beam parameters. A new simple and transparent method to calculate CBS is presented based on the equivalent photon approximation for this collective field. The results are applied to theφ-factoryDAΦNE. For this collider about 5·1014 d E γ/E γ photons per second are expected in the photon energyE γ range from the visible light up to 25 eV. 相似文献
6.
Coherent backscattering (CBS) of light in random media has been previously investigated by use of coherent light sources. Here we report a novel method of CBS measurement that combines low spatial coherence, broadband illumination, and spectrally resolved detection. We show that low spatial coherence illumination leads to an anomalously broad CBS peak and a dramatic speckle reduction; the latter is further facilitated by low temporal coherence detection. Thus CBS can be observed in biological tissue and other media that previously were beyond the reach of conventional CBS measurements. We also demonstrate, for the first time to our knowledge, spectroscopic analysis of CBS. CBS spectroscopy may find important applications in probing random media such as biological tissue in which depth-selective measurements are crucial. 相似文献
7.
Huang J Eradat N Raikh ME Vardeny ZV Zakhidov AA Baughman RH 《Physical review letters》2001,86(21):4815-4818
We studied coherent backscattering (CBS) of light from opal photonic crystals with incomplete band gaps. We observed a dramatic broadening of the CBS cone for incident angles close to the Bragg condition in the crystals. We modify the conventional CBS theory to incorporate Bragg attenuation resulting from the photonic band structure. By fitting the CBS data with the modified theory, we extract both the disorder-induced light mean-free path and the Bragg attenuation length of the inherent opal photonic crystal. 相似文献
8.
We consider coherent electromagnetic processes for colliders with short bunches, in particular the coherent bremsstrahlung
(CBS). CBS is the radiation of one bunch particles in the collective field of the oncoming bunch. It can be a potential tool
for optimizing collisions and for measuring beam parameters. A new simple and transparent method to calculate CBS is presented
based on the equivalent photon approximation for this collective field. The results are applied to theφ-factoryDAΦNE. For this collider about 5·1014
d
E
γ/E
γ photons per second are expected in the photon energyE
γ range from the visible light up to 25 eV. 相似文献
9.
10.
11.
We obtain analytic formulas for the frequency-dependent spin-Hall conductivity of a two-dimensional electron gas (2DEG) in the presence of impurities, linear spin-orbit Rashba interaction, and external magnetic field perpendicular to the 2DEG. We show how different mechanisms (skew scattering, side jump, and spin precession) can be brought in or out of focus by changing controllable parameters such as frequency, magnetic field, and temperature. We find, in particular, that the dc spin-Hall conductivity vanishes in the absence of a magnetic field, while a magnetic field restores the skew-scattering and side jump contributions proportionally to the ratio of magnetic and Rashba fields. 相似文献
12.
S. Pekárek 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2010,56(1):91-98
We have studied the effect of a stationary magnetic field on the production
of ozone from air at atmospheric pressure by a negative corona discharge in
a cylindrical electrode configuration. We used a stainless steel hollow
needle placed at the axis of the cylindrical discharge chamber as a cathode.
The outer wall of the cylinder was used as an anode. The vector of magnetic
induction was perpendicular to the vector of current density.
We found that: (a) the magnetic field extends the current voltage range of
the discharge; (b) for the discharge in the Trichel pulses regime and in the
pulseless glow regime, the magnetic field
has no substantial effect on the discharge voltage or on the concentration
of ozone that is produced; (c) for the discharge in the filamentary streamer
regime for a particular current, the magnetic field increases the discharge
voltage and consequently an approximately 30% higher ozone concentration
can be obtained; (d) the magnetic field does not substantially increase the
maximum ozone production yield. A major advantage of using a magnetic field
is that the increase in ozone concentration produced by the discharge can be
obtained without additional energy requirements. 相似文献
13.
Vainio O Ahokas J Novotny S Sheludyakov S Zvezdov D Suominen KA Vasiliev S 《Physical review letters》2012,108(18):185304
We present a high magnetic field study of electron spin waves in atomic hydrogen gas compressed to high densities of ~10(18) cm(-3) at temperatures ranging from 0.26 to 0.6 K. We observed a variety of spin wave modes caused by the identical spin rotation effect with strong dependence on the spatial profile of the polarizing magnetic field. We demonstrate confinement of these modes in regions of strong magnetic field and manipulate their spatial distribution by changing the position of the field maximum. 相似文献
14.
S. A. Koryagin 《Radiophysics and Quantum Electronics》2008,51(8):616-632
We analyze quantum-mechanically electron-ion collisions in a magnetic field at a low temperature, for which the electron's
thermal energy is less than the energy gap between two Landau levels and the electron's Larmor radius is less than the characteristic
impact parameter of close collisions without the magnetic field. To calculate transition probabilities, we use the analytical
procedure proposed in the first part of our paper. We calculate the energy and lifetime of the resonant (autoionization) states
of an electron embedded in the Coulomb electric field of an ion and in a uniform magnetic field. The obtained values coincide
in order of magnitude with the known exact numerical values. We find that the electron backward scattering probability irregularly
(chaotically) depends on the particle energy and the magnetic field. We propose analytical approximations for the collision
transport frequencies, one of which describes the electron braking along the magnetic field and another, equalizing of the
temperatures corresponding to the electron motion along and across the magnetic field.
Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 51, No. 8, pp. 682–699, August 2008. 相似文献
15.
C. P. Singh 《International Journal of Theoretical Physics》2014,53(5):1533-1546
In this paper we consider a spatially homogenous and anisotropic Bianchi type-V space-time model to investigate the effects of a magnetic field in string cosmology. We assume that the string’s direction and magnetic field are along x-axis. The field equations are solved by using the equation of state for a cloud of strings and variable magnetic permeability. We derive exact solutions for three types of strings: (i) Nambu strings, (ii) string model where the sum of energy density and string tension density is zero and (iii) Takabayasi strings. We examine the behaviour of scale factors and other physical parameters with and without magnetic field and it is found that the magnetic field effects the dynamics of the universe at early time. During late time the universe becomes isotropic even in the presence of magnetic field. The universe expands with decelerated rate during early stages of the evolution of the universe but it goes to marginal inflation at late times. 相似文献
16.
Buividovich PV Chernodub MN Kharzeev DE Kalaydzhyan T Luschevskaya EV Polikarpov MI 《Physical review letters》2010,105(13):132001
We study the correlator of two vector currents in quenched SU(2) lattice gauge theory with a chirally invariant lattice Dirac operator with a constant external magnetic field. It is found that in the confinement phase the correlator of the components of the current parallel to the magnetic field decays much slower than in the absence of a magnetic field, while for other components the correlation length slightly decreases. We apply the maximal entropy method to extract the corresponding spectral function. In the limit of zero frequency this spectral function yields the electric conductivity of quenched theory. We find that in the confinement phase the external magnetic field induces nonzero electric conductivity along the direction of the field, transforming the system from an insulator into an anisotropic conductor. In the deconfinement phase the conductivity does not exhibit any sizable dependence on the magnetic field. 相似文献
17.
I. V. Linchevskyi 《Optics and Spectroscopy》2013,115(5):696-700
We have considered the possibility of measuring the linear and quadratic (in magnetic field) magnetooptical effects in magnetooptical crystals that are simultaneously exposed to a constant (polarizing) magnetic field and to an alternating magnetic field under conditions of magnetomechanical resonance. The use of a Mueller polarimeter in combination with spectral analysis of the intensity of the light wave at the output of the polarimeter makes it possible to selectively determine elements of the Mueller matrix and minimize the amount of measurements. We have shown that there is a possibility of solving the inverse problem on finding two components of the alternating magnetic field in which a magnetooptical crystal is placed. 相似文献
18.
C. Lacroix M. Taillefumier V.K. Dugaev B. Canals 《Journal of magnetism and magnetic materials》2009,321(7):906-908
We study the energy spectrum and electronic properties of a two-dimensional (2D) spinless electron gas in a periodic magnetic field which has the symmetry of a triangular lattice. We show that the energy bands depend strongly on the value of the magnetic field. For large field the low-energy electrons are localized on closed rings where the magnetic field vanishes. This results in the appearance of persistent currents around these rings. We also calculate the intrinsic Hall conductivity, which is quantized when the Fermi level is in a gap. 相似文献
19.
We study the evolution equations of the distribution functions of hot electrons. We show that a convenient choice of the gauge describing the applied uniform electric and magnetic fields considerably simplifies the explicit calculations. The main advantage of our method lies in the possibility of treating with the same simplicity free electrons (with or without a magnetic field) and Bloch electrons (without a magnetic field). We discuss the influence of the electric field on the collision term of the different transport equations we derive. 相似文献
20.
We study theoretically the electronic and transport properties of a diffusive superconductor-normal metal-superconductor junction in the presence of a perpendicular magnetic field. We show that the field dependence of the critical current crosses over from the well-known Fraunhofer pattern in wide junctions to a monotonic decay when the width of the normal wire is smaller than the magnetic length xi(H)=square root Phi(0)/H, where H is the magnetic field and Phi(0) the flux quantum. We demonstrate that this behavior is a direct consequence of the magnetic vortex structure appearing in the normal region and predict how this structure is manifested in the local density of states. 相似文献