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Chinese Physics B

Nonlinear spectroscopy of barium in parallel electric and magnetic fields

Haifeng Yang, Wei Jia Gao, Hong Cheng, Hongping Liu

Published Oct 1, 2014• 0 citations
Publisher

Abstract

We report on the experimental spectral observations of barium in parallel electric and magnetic fields. The laser pulse is linearly polarized along or perpendicular to the fields, leading to the states m = 0 and the states m = ±1 populated, respectively, by one photon excitation. By sweeping the electric field, we observe the linear and nonlinear splitting of the diamagnetic spectrum as the electric field increases. The spectral anticrossing is induced by the atomic core effect. The Stark spectrum also shows an obvious nonlinear quadratic behavior when the applied magnetic field varies strongly. All spectra are well explained by the full quantum calculation after taking the quantum defect effects of the channel n s up to n f into account.

DOI
10.1088/1674-1056/23/10/103201

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We present observations of Stark spectra of barium in highly excited Rydberg states in the energy region around n = 35. The one-photon excitation concerns the π transition. The observed Stark spectra at electric fields ranging from 0 to 60 V·cm −1 are well explained by the diagonalization of the Hamiltonian incorporating the core effects. From the Stark maps, the anti-crossings between energy levels are identified experimentally and theoretically. The time of flight spectra at the specified Stark states are recorded, where the deceleration and acceleration of barium atoms are observed. This is very consistent with the prediction derived from the Stark maps from the point of view of energy conservation.
We study the core effect of nonhydrogenic alkaline-earth-metal barium in its diamagnetic spectrum by one photon transition from the ground state 6s26{s}^{2}6s2 1S0{}^{1}\phantom{\rule{-0.16em}{0ex}}{S}_{0}1S0​ experimentally and theoretically. The non-Coulombic potential of the ion core introduces an extra energy shift compared with hydrogen and a level anticrossing between different nnn manifolds, characterized by the quantum defect of the concerned angular momentum states. With a complex rotation coordinate technique and a BBB-spline expansion method, we develop a matrix-form Hamiltonian based on an effective potential incorporating the angular-dependent quantum defect into the angular rotation term. The nonhydrogen core effects are investigated by sweeping the quantum defects of different channels in the calculation. Results show that quantum defects of ppp and fff states have a undeniable effect on the intensities and positions of the spectral lines, although barium is closely hydrogenlike in the energy range examined. The anticrossing spectral lines are also identified with the aid of theoretical calculations. The calculations are in good agreement with the experimental observations.
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