We have made high-accuracy measurements of the integrated Stokes parameters for resonance fluorescence from polarized electron-impact excitation of the 4p 5 5p͓5/2͔ 3 D 3 and 4p 5 5p͓5/2͔ 3 D 2 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 P 2 signal relativistic effects ͑like continuum spin-orbit coupling, i.e., Mott scattering͒. A single value of P 2 ϭ4(4)ϫ10 Ϫ3 at 12.0 eV was previously reported in this energy range ͓Furst et al., Phys. Rev. A 47, 3775 ͑1993͔͒. We have now measured P 2 at six different energies in this region to comparable precision. These results are consistent with P 2 ϭ0 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 3 D 2 state. ͓S1050-2947͑99͒07907-X͔ PACS number͑s͒: 34.80.Dp
We have searched for evidence of electron circular dichroism, the preferential transmission of longitudinally polarized electrons through a chiral medium, using stereoisomers of camphor. Such an effect was seen by Campbell and Farago in 1987 for 5 eV electrons. Within our detection limit ( approximately 0.02%) we have not observed asymmetric transmission at either an incident electron energy of 1 eV or 5 eV. In preparation for this inquiry, we also measured the total scattering cross section for camphor in the energy range 0.5-5 eV.
We report operational and construction details of a simplified GaAs polarized electron source. It is contained in a modified 4.63 in. Conflat four-way cross, and uses a single 56 l /s turbomolecular pump. The design incorporates multiple cesiators to extend source lifetime, a new spring-clamp GaAs crystal mounting design to provide uniform crystal heating, and a very simple tubular 90°e lectrostatic deflector. We also discuss matters related to preparing, heat cleaning, and activating the GaAs crystal.
Analogous to optical circular dichroism, it is possible to have electron circular dichroism, the preferential transmission of longitudinally polarized electrons through a chiral medium. Using stereoisomers of camphor vapor as a scattering target, we looked for this effect at incident electron energies of 1, 3, 5, 7, or 10 eV. Within our detection limit (~0.02%) we have not observed a spin-dependent asymmetric transmission.
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