In the last 30 days

• Open/close Frequency-dependent dipole shielding factors

  V G Kaveeshwar et al 1969 J. Phys. B: At. Mol. Phys. 2 984 Tag this article

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  A frequency-dependent dipole shielding factor β _infinity(ω) is defined as the coefficient of proportionality between the electric-dipole induced field and a uniform external electric field, at the nucleus, when the external field varies sinusoidally with time and with circular frequency ω. From oscillator sum rules it is shown that β _infinity(ω) = N/ Z ₀ + ω ²α(ω)/ Z ₀ where N is the number of electrons, Z ₀ is the nuclear charge and α(ω) is the dynamic dipole polarizability. Numerical calculations of β _infinity(ω) are reported for He, Be, Ne and several ions using coupled Hartree-Fock theory. It is found that calculations of β _infinity(ω) provide a severe test of the accuracy of zero- and first-order frequency-dependent wave functions.

• Open/close Effective collision frequency of electrons in noble gases

  P Baille et al 1981 J. Phys. B: At. Mol. Phys. 14 1485 Tag this article

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  The electron-neutral collision frequency in the noble gases has been calculated using recent numerical results for momentum transfer cross sections by assuming a Maxwellian distribution of electron velocities. In all these gases, except for argon, good agreement is obtained with most previously published experimental and theoretical data. Mean free path, mobilities and diffusion coefficients are also calculated from the resulting effective collision frequencies. The empirical formulae are presented for an electron temperature dependence of the electron-neutral collision frequency for all noble gases up to T _e<or=25000K.

• Open/close Steady-state quantum interference in resonance fluorescence

  D A Cardimona et al 1982 J. Phys. B: At. Mol. Phys. 15 55 Tag this article

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  It is shown that when a monochromatic laser couples a single atomic ground level to two closely spaced excited levels the system can be driven into a state in which quantum interference prevents any fluorescence from the excited levels, regardless of the intensity of the exciting field. This steady-state interference occurs only at a particular excitation frequency which depends on the separation of the excited states and the relative size of the two transition dipole matrix elements. The results are derived from the density matrix equations of motion. It is shown that a correct description of the effect requires the inclusion of generalised Einstein A coefficients which are usually neglected in phenomenological damping theories. A dressed-state analysis is introduced to simplify the generalisation to atoms having more complex manifolds of excited states. Analogous interferences in multiphoton absorption and ionisation are also discussed briefly.

• Open/close On the generalized Einstein relation for gaseous ions in an electrostatic field

  R E Robson 1976 J. Phys. B: At. Mol. Phys. 9 L337 Tag this article

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  Momentum-transfer theory shows that an additional factor involving heat flux must appear in the generalized Einstein relation as first proposed by Wannier (1953) for gaseous ions in an electrostatic field. The correction is most significant in cases where the ion mass is comparable with the mass of gas atoms.

• Open/close Dressed-atom description of resonance fluorescence and absorption spectra of a multi-level atom in an intense laser beam

  C Cohen-Tannoudji and S Reynaud 1977 J. Phys. B: At. Mol. Phys. 10 345 Tag this article

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  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.

• Open/close Highly excited levels of neutral ytterbium. II. Multichannel quantum defect analysis of odd- and even-parity spectra

  M Aymar et al 1980 J. Phys. B: At. Mol. Phys. 13 1089 Tag this article

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  For pt.I see ibid., vol.13, no.6, p.1073 (1980). Data on the bound even-parity spectrum of Yb have been presented in the preceding paper (Carnus et al., 1980). These data provide an excellent opportunity for the application of multichannel quantum defect theory (MQDT) to this spectrum. The bound even-parity J=0, 2 spectra and the bound odd-parity J=1 spectrum are analysed with MQDT models. The behaviour of the even-parity 4f ¹⁴6sns ¹S ₀ (n>or=7) and 4f ¹⁴6snd ^1.3D ₂ (n>or=8) Rydberg series perturbed by levels of the 4f ¹⁴6p ² and 4f ¹³5d6s6p configurations is well interpreted; in the same way the known bound levels of the 4f ¹⁴6snp ^1.3P ₁ Rydberg series (n>or=12) perturbed by levels of the 4f ¹³5d ²6s configuration are well interpreted. The mutual interaction of the singlet and triplet levels of J=1 and J=2 Rydberg series is analysed. Some assignments of levels are changed and predicted energy values are given for many levels.

• Open/close Population trapping and dispersion in a three-level system

  P M Radmore and P L Knight 1982 J. Phys. B: At. Mol. Phys. 15 561 Tag this article

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  The population dynamics and spectra of a three-level system driven by two applied fields of arbitrary amplitudes and detunings are examined using dressed-state techniques. The authors report the existence of novel dispersive features in the variation with detuning of the intermediate-state population.

• Open/close Time-dependent theory of non-Hermitian Schrodinger equation: Application to multiphoton-induced ionisation decay of atoms

  F H M Faisal and J V Moloney 1981 J. Phys. B: At. Mol. Phys. 14 3603 Tag this article

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  A rigorous and practical time-dependent formulation of quantum decay processes is obtained by converting the Hermitian Schrodinger problem into an equivalent non-Hermitian Schrodinger equation. The properties of the original Hermitian and the reduced non-Hermitian Hamiltonians are compared and the non-Hermitian formulation is shown to be consistent with the theorem of Fock and Krylov for the description of truly decaying states. A self-consistent non-unitary algorithm is developed and used to obtain expressions for the time-dependent transition amplitudes of interest; they automatically preserve the total probability in the sum space at all future times tau >0. The formalism is coded for application to the important problem of ionisation decay of a ground-state hydrogen atom coupled to a strong radiation field with a sub-threshold photon frequency. The first quantitative information on the time dependence of two- and three-photon (resonant and non-resonant) ionisation of the hydrogen atom is obtained.

• Open/close AC Stark splitting of photoelectron energy spectra in multiphoton ionisation

  P L Knight 1978 J. Phys. B: At. Mol. Phys. 11 L511 Tag this article

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  Autler-Townes splitting of photoelectron energy distributions in resonant two-photon ionisation is predicted using standard Heitler-Ma techniques.

• Open/close Collision problems with identical particles

  F Masnou-Seeuws and A Salin 1969 J. Phys. B: At. Mol. Phys. 2 1274 Tag this article

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  Attention is drawn to a method, formulated by Feynmann, which gives a straightforward derivation of the cross section in the case of collisions between identical particles. The difficulties encountered in the interpretation of the scattering amplitudes are stressed when the wave function is symmetrized. Ways of avoiding these difficulties are discussed, showing that it is easier to refer to physical experiments with fixed apparatus.