Spectroscopy of Rydberg Atomic Systems in a Black-Body Radiation Field
53
From a physical point of view, there is a spontaneous transformation of the cloud
of cold Rydberg atoms into supercooled plasma in magneto-optical traps due to
avalanche ionization by thermal BBR radiation. Naturally, the study of different
elementary processes involving Rydberg atoms in the BBR radiation field has been
considered in a fairly large number of works.
The vast majority of existing papers on the description of Rydberg atoms in the
thermal radiation field (c.g. [1–32]) are based on the Coulomb hydrogen-like approximation, different versions of the quantum defect method, classical and quasiclassical model approaches, the model and pseudo—potential methods. The authors of
the papers [3–10] applied the Coulomb approximation, quantum defect formalism,
different versions of the model and pseudo-potential method etc. (as a rule, the nonrelativistic versions are used) to determine the spectral and radiative properties of
different Rydberg atoms and ions.
It should be noted separately the cycles of theoretical and experimental works by
Ryabtsev-Beterov et al. [1–3, 13–16], as well as theoretical works of Gorelovsky
et al., Dyachkov-Pankratov and others (c.g. [7]), in which the advanced versions
of a quasi-classical approach to the calculation of radiation amplitudes, oscillator
strengths, and cross-sections for the Rydberg atoms in the BBR radiation field were
actually developed. In the papers [1–3, 13–16] the authors present the calculational
data on the ionization rates for Rydberg atoms of alkali elements (lithium, sodium,
potassium, caesium) by a BBR radiation field. The calculations were carried out
for the nS, nP, and nD states in the wide range of principal quantum numbers and
temperatures. The above theoretical works and relevant models were substantially
based on non-relativistic approximation.
At the same time one should note that for heavy Rydberg atoms (both in the free
state and in an external electromagnetic field) it is fundamentally important to accurately account for both relativistic and exchange-correlation effects. The quality and
consistency of accounting for these effects also determine the accuracy of description
of the energy and spectroscopic parameters of the heavy Rydberg atoms, including
these atoms in a thermal radiation field.
Among the fundamentally important exchange-correlation effects for essentially
many-electron systems, one should single out such effects as polarization interaction
and screening, continuum pressure, the non-Coulomb grouping of levels in the heavy
Rydberg atoms spectra etc. It should be noted that these effects are not correctly considered, for example, within simplified Coulomb approximation or quantum defect
models (c.g. [50, 51, 62–64]).
Another important point in studying different properties of heavy multi-electron
atoms is related to the need to use optimized bases of relativistic wave functions,
which is directly related to fulfilling the principle of gauge invariance. In fact
this point is directly connected with an accurate consideration of the multielectron exchange-correlation effects. Here one should single out the gauge dependent
contributions into the imaginary part of the electron energy shift (radiation width
or transition probability or oscillator strength) for the certain class of the photon
propagators (c.g. [56–61]).
53
From a physical point of view, there is a spontaneous transformation of the cloud
of cold Rydberg atoms into supercooled plasma in magneto-optical traps due to
avalanche ionization by thermal BBR radiation. Naturally, the study of different
elementary processes involving Rydberg atoms in the BBR radiation field has been
considered in a fairly large number of works.
The vast majority of existing papers on the description of Rydberg atoms in the
thermal radiation field (c.g. [1–32]) are based on the Coulomb hydrogen-like approximation, different versions of the quantum defect method, classical and quasiclassical model approaches, the model and pseudo—potential methods. The authors of
the papers [3–10] applied the Coulomb approximation, quantum defect formalism,
different versions of the model and pseudo-potential method etc. (as a rule, the nonrelativistic versions are used) to determine the spectral and radiative properties of
different Rydberg atoms and ions.
It should be noted separately the cycles of theoretical and experimental works by
Ryabtsev-Beterov et al. [1–3, 13–16], as well as theoretical works of Gorelovsky
et al., Dyachkov-Pankratov and others (c.g. [7]), in which the advanced versions
of a quasi-classical approach to the calculation of radiation amplitudes, oscillator
strengths, and cross-sections for the Rydberg atoms in the BBR radiation field were
actually developed. In the papers [1–3, 13–16] the authors present the calculational
data on the ionization rates for Rydberg atoms of alkali elements (lithium, sodium,
potassium, caesium) by a BBR radiation field. The calculations were carried out
for the nS, nP, and nD states in the wide range of principal quantum numbers and
temperatures. The above theoretical works and relevant models were substantially
based on non-relativistic approximation.
At the same time one should note that for heavy Rydberg atoms (both in the free
state and in an external electromagnetic field) it is fundamentally important to accurately account for both relativistic and exchange-correlation effects. The quality and
consistency of accounting for these effects also determine the accuracy of description
of the energy and spectroscopic parameters of the heavy Rydberg atoms, including
these atoms in a thermal radiation field.
Among the fundamentally important exchange-correlation effects for essentially
many-electron systems, one should single out such effects as polarization interaction
and screening, continuum pressure, the non-Coulomb grouping of levels in the heavy
Rydberg atoms spectra etc. It should be noted that these effects are not correctly considered, for example, within simplified Coulomb approximation or quantum defect
models (c.g. [50, 51, 62–64]).
Another important point in studying different properties of heavy multi-electron
atoms is related to the need to use optimized bases of relativistic wave functions,
which is directly related to fulfilling the principle of gauge invariance. In fact
this point is directly connected with an accurate consideration of the multielectron exchange-correlation effects. Here one should single out the gauge dependent
contributions into the imaginary part of the electron energy shift (radiation width
or transition probability or oscillator strength) for the certain class of the photon
propagators (c.g. [56–61]).