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Acta Physica Sinica

SPECTRUM CHARACTERISTICS OF AN ATOM IN A STRONG MAGNETIC FIELD

HE XING-HONG, ZHOU FENG-QING, Baiwen Li, ZHANG CHENG-XIU, (1)中国科学院武汉物理研究所波谱与原子分子物理开放研究实验室,武汉430071; (2)中国科学院武汉物理研究所波谱与原子分子物理开放研究实验室,武汉430071;华中理工大学激光技术国家实验室,武汉430074

Published Jan 1, 1992• 0 citations
Publisher

Abstract

A perturbation method is used to evaluate the energy levels and oscillator strengths of sodium atoms (m=-2,π2=+)in a strong magnetic field. The main features of the calculated spectra which lie in the strong-field-mixing regime agree well with the corresponding experimental results. Besides the conventional quasi-Landau resonance with spacing equal to 1.5?ωc (ωc is the electron cyclotron frequency) near the zero field ionization limit, a series of resonance spacings are found and analysed using the zero order energy formula and the Fourier transform technique. The values of these spacings are in consistent with other theoretical results. Based on the perturbation method, a quantum mechanical explanation for the spacings is given. These resonance spacings are independent of the applied exernal magnetic field.

DOI
10.7498/aps.41.1244

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A perturbation method is used to evaluate the energy levels and oscillator strengths of sodium atoms (m=-2,π2=+)in a strong magnetic field. The main features of the calculated spectra which lie in the strong-field-mixing regime agree well with the corresponding experimental results. Besides the conventional quasi-Landau resonance with spacing equal to 1.5?ωc (ωc is the electron cyclotron frequency) near the zero field ionization limit, a series of resonance spacings are found and analysed using the zero order energy formula and the Fourier transform technique. The values of these spacings are in consistent with other theoretical results. Based on the perturbation method, a quantum mechanical explanation for the spacings is given. These resonance spacings are independent of the applied exernal magnetic field.
Quasi-Landau resonances have been recorded for lithium atoms in magnetic fields of up to 47 kG, with a spacing of only half the cyclotron frequency rather than 32\frac{3}{2}23​ as expected from previous theory. The intensity distribution over satellites in the lll-mixing region (including the appearance of parity-forbidden transitions) is discussed in terms of magnetic mixing among nearly degenerate levels. An intensity sum rule is demonstrated.
Abstract We present a systematic densitometer mapping of diamagnetic effects on the principal series of Ba and Sr in absorption, with magnetic fields up to 4.7 T. The n- and l-mixing spectra are resolved in both σ- and π-polarization while the quasi-Landau resonances are observed near and above the ionization limit only in σ-polarization. Configuration interaction produces striking differences in the intensities and spacings of the n- and l-mixed spectra while only the shapes of the quasi-Landau resonances depend on the atomic systems.
The diamagnetic and Stark shifts of strongly perturbed Rydberg spectra such as those of the alkaline earths are expressed in terms of multichannel---quantum-defect parameters. The theory is applicable when the shifts produced by the external fields are smaller than the neighboring Rydberg separations. It is applied to evaluate the diamagnetic shifts in Ba, an atom in which Rydberg and doubly excited channels are strongly mixed. In such complex spectra, the diamagnetic effect can serve a useful purpose as a tool to disentangle the interacting series. The radial sizes and, therefore, the diamagnetic shifts are quite different for singly and doubly excited states even when they are at the same energy. In fact, for the field strengths considered ($\ensuremath{\simeq}40$ kG), the diamagnetic contribution of the doubly excited configuration is quite negligible. As a result, the observed shift is a direct measure of the amount of singly excited configuration in the state of interest. Exactly similar conclusions apply to Stark shifts. The last part of this paper considers states of very high excitation further up in the spectrum which are no longer in a perturbative regime. Spectra of atoms in a magnetic field have shown equally spaced resonances near the ionization threshold with characteristic spacings. By the consideration of the effects of electric fields which are also often simultaneously present, a criterion is established for the nature of these spacings depending on the relative strengths of the crossed electric and magnetic fields. The spacing seen in any particular experiment is shown to depend on the mass and quantum defect of the atom, the strengths of the external fields, and experimental conditions such as the temperature of the atomic vapor whose absorption spectrum is being studied.
In this chapter experiments on rubidium Rydberg atoms in external fields are reviewed [1 – 8]. In the first part results on the interaction of microwave radiation with rubidium Rydberg atoms are described. The Rydberg atoms interact with a microwave pulse of a well-defined duration. When applying coherent microwave radiation with a frequency exceeding a certain value, the experimentally observed microwave field strength at which 10% of the atoms are ionized has to be much larger than the value found by classical trajectory calculations. The atoms are stabilized by the dynamical localization. An extremely weak microwave broadband noise which is added to the coherent wave at least partially destroys the localization. This phenomenon depends on the bandwidth of the added noise. In further experiments the dependence of the 10% ionization microwave field strength on the duration τ of the microwave pulse has been investigated. For increasing noise level the 10% ionization field strength ∈ 0.1 develops from a behavior ∈ 0.1 ∼ τ −1/4 to a ∈ 0.1 ∼ τ −1/2 dependence, which is characteristic for a classical diffusion process. The second part of the chapter deals with experiments in strong static crossed electric and magnetic fields. Below as well as above the ionization energy the observed quasi-Landau(QL)-resonances are explained using classical trajectories. The ionization behavior of the QL-resonances is clearly influenced by the spatial structure of the associated classical orbits. In further experiments the dependence of the observed ionization energy on the magnetic field was investigated in the presence of a fixed static electric field.
We report diamagnetic spectra of sodium atoms observed in a strong magnetic field up to 3 T and compare them with theoretical calculations based on the formulation of an exact quantum-defect theory. We focus on one-photon absorption processes from the ground 3s3s3s state to the excited npnpnp Rydberg states whose magnetic quantum numbers are determined by the polarization of the laser field. The calculations employ BBB-spline basis expansion and the complex spatial coordinate rotation technique, and their results agree well with the observed ones when atomic core effects are appropriately taken into account. When graphed against magnetic field, level anticrossings and core-induced interaction of the npnpnp states provide clear signatures for studying the effects of quantum defect on the diamagnetic spectra.