A dressed-atom approach to resonance fluorescence in intense laser fields is presented. Simple and general results are derived which include the now well known predictions concerning two-level atoms but are not restricted to such simple cases. The positions of the various components of the fluorescence and absorption spectra are given by the allowed Bohr frequencies of the total system: atom+laser mode (dressed atom). The master equation, describing spontaneous emission from the dressed atom is solved in the limit of high intensities. Simple expressions, taking into account the effect of cascades, are derived for the widths of the components.
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C Cohen-Tannoudji and S Reynaud 1977 J. Phys. B: Atom. Mol. Phys. 10 345
I P Grant 1974 J. Phys. B: Atom. Mol. Phys. 7 1458
The gauge invariance of the matrix elements of electromagnetic interaction is a property that is usually taken for granted. The author describes a unified derivation in which the dependence of the matrix elements on the gauge in which the electromagnetic potentials are written is exhibited explicitly. The necessary and sufficient condition for the transition matrices for all multipoles to be gauge invariant is that the transition matrix for longitudinal photons should vanish identically. This imposes conditions on the initial and final wavefunctions which are automatically satisfied for a single-particle model but may not necessarily hold in, say, the Hartree-Fock model. For electric dipole transitions, it is shown that the Coulomb gauge leads to the dipole velocity form of the matrix element in the nonrelativistic limit and that a different choice is needed to give the dipole length form. Arguments are advanced suggesting that the dipole velocity form should be given a privileged position in approximate calculations of atomic and molecular transition probabilities.
I P Grant and N C Pyper 1976 J. Phys. B: Atom. Mol. Phys. 9 761
The Breit interaction which gives the leading correction to the Coulomb potential in quantum electrodynamics, is required for precision calculations of binding energies of inner electrons in heavy atoms for calculations of multiplet structure, and for other applications. The correct form for use in multi-configuration calculations is discussed, and the angular momentum reduction to a sum of radial integrals is carried out completely in an approximation valid for all problems except those involving very tightly bound electrons. The coefficients are presented in a form suitable for computation; a computer program for matrix elements of the Breit interaction for general atomic states is at present under test.
U Wille 1987 J. Phys. B: Atom. Mol. Phys. 20 6669
H J Carmichael 1980 J. Phys. B: Atom. Mol. Phys. 13 3551
The cooperative resonance fluorescence steady state is discussed within the context of an operator master equation which conserves total pseudospin. Emphasis throughout is on quantum fluctuations and their significance in relation to a background of factorised dynamics. Atom-atom correlations are shown to play a fundamental role for systems driven beyond the linear regime. Use of the atomic coherent state representation yields a Fokker-Planck description closely allied to the dynamics for a classical angular momentum oscillator. For intense incident fields the quantum-mechanical steady state is understood in terms of diffusion both around and between classical trajectories on the Bloch sphere. In the limit of infinite systems simple closed-form expressions for steady-state features are derived. Coherent and incoherent fluorescent intensities are obtained together with the second-order correlation function for fluorescent light. Specific features are illustrated by numerical results for systems of from two to fifty atoms.
H J Blaauw et al 1977 J. Phys. B: Atom. Mol. Phys. 10 L299
An apparatus has been constructed to measure the total cross section for electron scattering by atoms and molecules. It can be viewed as a linearisation of the Ramsauer technique with a well defined solid angle for the analyser/collector. Measurements of He and N2 have been carried out for 15-750 eV electrons. The data obtained link up with the existing data at low energies within the experimental uncertainty. For He perfect agreement is found with the Born approximation above 200 eV.
A Crubellier et al 1985 J. Phys. B: Atom. Mol. Phys. 18 3811
This paper is the first of a sequence of four papers devoted to the theoretical study of subradiance, i.e. of the cooperative inhibition of spontaneous emission, a phenomenon which has been recently observed. It is shown, in the typical example of a pencil-shaped sample of three-level atoms in the 'V' configuration (two transitions sharing a common lower level), that the system can spontaneously reach a state in which the emission in the so-called 'end-fire' superradiant field modes is cooperatively inhibited; this occurs for initially uncorrelated atoms when the initial state is a statistical mixing of the two upper states. The whole study is centered on the concept of destructive interatomic interference and it is therefore based on the symmetry properties of the collective atomic state with respect to the permutations of locally indistinguishable atoms. Semiclassical and fully quantum-mechanical models are used in turn. The obstacles to the interatomic interference and thus to subradiance are finally discussed.
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U Wille 1987 J. Phys. B: Atom. Mol. Phys. 20 6669
M Kimura et al 1987 J. Phys. B: Atom. Mol. Phys. 20 6670
N N Choi et al 1987 J. Phys. B: Atom. Mol. Phys. 20 L827
Non-relativistic rates for the decay of 2s hydrogen atoms to the ground state by single-photon and two-photon emission in the presence of a homogeneous magnetic field of arbitrary strength (0<or=B<or=4.7*106 T) are calculated by variational procedures. Over the whole range of B, two-photon emission is the dominant process. As the magnetic field grows, the two-photon decay rate increases. It is found that the Markov approximation can be applied to the two-photon decay for magnetic fields of strength B>or=4.7*103 T.
B Wallbank et al 1987 J. Phys. B: Atom. Mol. Phys. 20 L833
Differential cross sections for the one-photon emission free-free process are measured as a function of laser intensity when 10.55 eV electrons are scattered from argon atoms in the presence of a pulsed CO2 laser. The cross sections are reported for both single longitudinal-mode and multimode laser pulses up to an intensity of 2*107 W cm-2. For intensities less than 2*106 W cm-2, the cross sections for both laser pulses are found to be linear with intensity, in agreement with perturbation theory. At higher intensities comparisons are made with predictions based on the low-frequency approximation and two laser models. The linear parts of the cross sections are used to obtain estimates of the spatial inhomogeneities in the electron-laser interaction region. Reasonable agreement is found between the experimental cross sections and those predicted by the two laser models.
Y Vitel and M Skowronek 1987 J. Phys. B: Atom. Mol. Phys. 20 6477
Stark widths and shifts of the Ar I 696.5 nm and of the Ar II 480.6, 484.7 and 434.8 nm lines have been measured in the range of electron density and temperature 0.6-1.5*1018 cm-3, 16200-18700 K. These high-density plasmas are created in linear flash-tubes. The plasma parameters are principally determined by measurements of the continuum radiation, from the intensity of optically thick lines in their centre and by the condition of local thermodynamic equilibrium of the plasma. The electron density and temperature radial profiles so deduced are found to be practically flat over more than half of the tube radius. In this quasi-stationary stage of the plasma, the experimental line profiles are recorded by an optical multichannel analyser coupled with a high-dispersion spectrometer. The profiles are analysed and fitted to a Lorentzian function. The Stark parameters, width and shift, show a non-linear dependence against the electron density.
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B E J Pagel 1971 J. Phys. B: Atom. Mol. Phys. 4 279
The following applications of spectral line broadening theory to astrophysics are briefly reviewed: (i) understanding qualitative effects visible on spectrograms; (ii) quantitative understanding of hydrogen-line profiles for the determination of stellar atmospheric parameters; (iii) effects of line broadening on the determination of stellar chemical composition.