A beam of unpolarized electrons is crossed at right angles with a beam of partially polarized sodium or potassium atoms (degree of polarization P A approximately=21%) and resonance lines from the excited 2 P 3/2, 1/2 states are observed in a direction perpendicular to both the atom and electron beams for electron energies from threshold to 200 eV. The polarization of the emitted photons is measured in the form of the Stokes parameters P 1 , P 2 and P 3 . The present measurements for sodium atoms are in better agreement with the theoretical values than the previously published experimental results. No other experimental or theoretical results are available for potassium atoms.
A beam of unpolarized electrons is crossed at right angles with a beam of partially polarized sodium or potassium atoms (degree of polarization P A approximately=21%) and resonance lines from the excited 2 P 3/2, 1/2 states are observed in a direction perpendicular to both the atom and electron beams for electron energies from threshold to 200 eV. The polarization of the emitted photons is measured in the form of the Stokes parameters P 1 , P 2 and P 3 . The present measurements for sodium atoms are in better agreement with the theoretical values than the previously published experimental results. No other experimental or theoretical results are available for potassium atoms.
A beam of unpolarised electrons is crossed at right angles with a beam of partially polarised sodium or potassium atoms (degree of polarisation PA = 21%). The resonance radiation from excited 2P3/2,1/2 states is observed in a direction perpendicular to both beams, and the Stokes parameters P1, P2 and P3, of the emitted photons are measured, \n \n[equation omitted] \n \nwhere 0 degrees, 45 degrees, 90 degrees and 135 degrees corresponds to the polariser angle measured from the electron beam direction and RHC, LHC to right and left hand circular polarisation in the spectroscopic definition. Because of reflection symmetries, only P1 is expected to be non-zero for unpolarised atoms. If polarised atoms are used with their spins parallel to the direction of the observed photons, P3 should also become non-zero (in addition to P1) while P2 remains zero. Such an experiment was originally proposed by Kleinpoppen, Phys. Rev. A3, 2015 (1971). \n \nWe report here an independent measurement on the neutral sodium NaI (32P3/2,1/2 – 32S1/2) transition (lambda = 589.0, 589.6 nm) and present new results for the neutral potassium KI (52P3/2,1/2 – 42S1/2) transition (lambda = 404.4, 404.7nm). The sodium results show close similarities to the work done by S. Osimitsch, Diplomarbeit Universitat Bielefeld (1983) and Jitschln at al J. Phys. B 17 1899 (1984) especially for P1 and P2. \nThe potassium results for P2 agree well with the theoretical prediction of zero and the results for P1 show close similarities to those of sodium results at high and intermediate energies, while at low energy especially close to threshold they differ. The threshold polarisation (P1) in the case of potassium is about 10%. Our values for sodium are somewhat higher than the results of Osimitsch (1983) and Jitschin et al (1984) and in very close agreement with the theoretical work done by Moores and Norcross, J. Phys. B5, 1482 (1972) and Kennedy et al, J. Phys. B10 3759 (1977) .The trend of P3 for potassium is similar to that of sodium in such a way that it is low at low energy and Increases in value as the energy increases, until it reaches a limit of 17% at high energy. The circular polarisation, P3, depends on the particular interaction processes which took place. At low energy, the three interaction channels, the exchange, the direct and the interference interaction are comparable and this will explain the low value of P3, at low energy due to spin flips of the electron of the atom in the exchange processes. At high energy the circular polarisation P3, is high which indicates that the exchange processes are minimal.
Polarized radiation following electron impact.---If a unidirectional beam of electrons, of velocity slightly in excess of the resonance potential, is projected through a vapor at a very low pressure so that effects due to atomic collision and resonance radiation are negligible, and in the absence of an applied field and resulting Larmor precession, there is reason to suspect that the radiation emitted perpendicular to the electron beam should be partially polarized, especially for lines corresponding to $\ensuremath{\Delta}j=1$.Polarization in mercury and sodium vapor.---Experiment showed a polarization of about 30 percent for $\ensuremath{\lambda}2537$ with the greatest intensity of the electrical vibration having a direction perpendicular to the electron beam. No polarization was detected for the unresolved sodium D-lines, confirming the recent observation of Kossel and Gerthsen.Polarization in mercury with field of 3 gauss.---A field parallel to the electron beam produced no effect. With the field perpendicular to the beam the radiation along the field was unpolarized while that perpendicular to the field was reduced in polarization to 13 percent. These results suggest that the atom radiates with the same distribution of polarization and intensity as in zero field but with the atom rotated through an angle determined by the time of excitation and the precessional velocity.
The relative optical excitation functions and polarizations of the Sr resonance line (4607 \AA{}) and of the Sr+ resonance lines (4078 and 4216 \AA{}) have been measured, using crossed electron and strontium-atom beams, for electron energies from the excitation thresholds to 1497 eV. The electron-beam energy resolution was \ensuremath{\sim} 0.22 eV for energies below 13 eV, and the atom beam was optically thin. The excitation functions of the ionic lines were measured relative to that of the atomic resonance line at fixed energies near the maxima of the excitation functions. Using spontaneous-emission branching ratios, this yields the ratios of total excitation cross sections for the atomic and ionic resonance levels (including cascades). The Sr 51P excitation function has been normalized to Born theory taking account of cascade at 1497 eV, where the energy dependence of the excitation function has converged to the theoretical behavior. The resulting normalized cross sections have been compared with available theoretical calculations and other measurements. The 4607-\AA{} polarization function is consistent with the theoretical threshold limit within experimental uncertainity.
General expressions are derived and investigated for the degree of polarization of electrons as a result of resonant two-photon ionization of unpolarized atoms having the S state as the ground state. The exciting and ionizing electromagnetic fields have arbitrary degrees of polarization and directions of propagation. It is shown that in cases where the matrix elements of P → S transitions from the resonant state to the continuum predominante over the matrix elements of P → D transitions, completely polarized photoelectrons may be obtained. These cases are found for sodium and potassium atoms.
We have measured the relative optical-excitation functions and polarizations of the K, Rb, and Cs resonance lines, using crossed electron and atom beams, for electron energies from threshold to 1500 eV. The electron energy resolution was \ensuremath{\sim}0.25 eV for energies below 13 eV, and the atom beam was optically thin. The atomic resonance-level (n2P) excitation functions have been normalized to the Born theory in the high-energy limit. Comparisons are made with other measurements and calculations. The polarizations and total cross sections for H, Li, Na, K, Rb, and Cs are also compared with each other in reduced units to investigate systematic behavior.
Abstract The dipole radiation emitted by an atom excited by a unidirectional electron beam has a nonuniform angular distribution which is simply related to the percentage polarization P of the radiation emitted perpendicular to the beam. P was first calculated using the OppenheimerPenney (O.-P.) theory. In this theory the probability of excitation of an upper quantum state and the probability of subsequent emission of a polarized photon from such a state are considered independently. P is finally expressed in terms of the cross-sections QM for excitation of states of definite component of angular momentum along the direction of the electron beam. In general, P is dependent on detailed numerical calculations of QM j, but the selection rule A = 0 removes this dependence at threshold. In the O.-P. theory allowance may be made for fine structure and hyperfine structure, but the theory is ambiguous when the f.s. or h.f.s. separations are comparable with the line width. A theory is therefore developed which is based on the calculation of the probability of a polarized photon being emitted by the complete system of atom + electron. The ambiguity of the O.-P. theory is removed by integration over line profiles, but the expressions reduce to O.-P. expressions when the f.s. or h.f.s. separations are much smaller or much larger than the line width. The Lyot line of hydrogen is an intermediate case for which the line widths and the h.f.s. separations are comparable. Assuming the validity of the Born approximation, a simple expression is obtained which allows the QM to be calculated from the angular distribution of the scattered electrons. Theoretical predictions are compared with experimental results. For the Na£) lines the predicted polarization is small enough to escape experimental detection. Polarizations observed by - Skinner & Appleyard in 1927 for various Hg lines rise to maxima with decreasing electron energy, and then tend to values close to zero at threshold. These experimental results at low energies appear to be inexplicable in terms of the reactions considered, but if the polarization curve above the maximum is extrapolated to threshold, the theory and experiment are found to be in reasonable agreement. Further experimental work is thought to be desirable