Near-threshold measurement of integrated Stokes parameters for Kr excited by polarized electrons

Authors

B. G. Birdsey, University of Nebraska - Lincoln
H. M. Al-Khateeb, University of Nebraska - Lincoln
M. E. Johnston, University of Nebraska - Lincoln
T. C. Bowen, University of Nebraska - Lincoln
Timothy J. Gay, University of Nebraska - LincolnFollow
V. Zeman, University of Nottingham, Nottingham NG7 2RD, United Kingdom
K. Bartschat, Drake University, Des Moines, Iowa

Date of this Version

August 1999

Comments

Published in PHYSICAL REVIEW A, VOLUME 60, NUMBER 2, AUGUST 1999. ©1999 The American Physical Society. Used by permission.

Abstract

We have made high-accuracy measurements of the integrated Stokes parameters for resonance fluorescence from polarized electron-impact excitation of the ⁴p⁵5p[5/2] ³D₃ and ⁴p⁵5p [5/2] ³D₂ states of Kr. We report measurements in the region within 0.6 eV of threshold, which is below the first cascade threshold. We also present theoretical calculations of these Stokes parameters using a recently developed relativistic Breit-Pauli Rmatrix code. In well LS-coupled systems, nonzero values of the integrated Stokes parameter P₂ signal relativistic effects (like continuum spin-orbit coupling, i.e., Mott scattering). A single value of P₂=4(4)310^-3 at 12.0 eV was previously reported in this energy range [Furst et al., Phys. Rev. A 47, 3775 (1993)]. We have now measured P₂ at six different energies in this region to comparable precision. These results are consistent with P₂=0 and with the theory. We discuss the effect of the electron-beam energy width on the accuracy of the measurements. Even when such effects are accounted for, serious discrepancies remain between theoretical and experimental results for excitation of the intermediately coupled ³D₂ state.