A measurement of electron impact coherence parameters by superelastic scattering from laser-excited¹³⁸Ba (. . . 6s6p¹P₁)

Abstract

Superelastic scattering of electrons from laser-excited 138Ba (. . . 6s6p 1P1) is used to measure the electron impact coherence parameters for excitation of this state. In particular, the variation with scattering angle of the charge cloud asymmetry parameter, Pl+, and the alignment angle parameter, gamma , have been determined at two incident electron energies. Comparison with recent theoretical results based on the unitarized distorted wave approximation has been made taking into account any possible distortion in the measurements due to the influence of a finite interaction volume. This comparison reveals good quantitative agreement for the gamma parameter over the range of scattering angles studied. Differences between the observed and predicted Pl+ parameters are small for near-forward scattering but become significant at the larger scattering angles studied.

Preparation of Al–O–N Films by Electron Cyclotron Resonance Plasma-Assisted Chemical Vapor Deposition

“…As a result, we have been motivated to carry out such measurements. The present set of measurements extends our previous results at impact energies of 20, 36.7, 50 and 80 eV (Li and Zetner 1994a, Zetner et al 1992, 1993 into the low impact energy regime (5, 7.5, 9, 10 and 15 eV). This paper is organized as follows.…”

“…Further measurements on Sr were reported by Beyer et al (1994). Superelastic scattering measurements applied to the determination of EICP for s-p excitations in two-electron systems have been reported for Ca (Law and Teubner 1995), Yb (Li and Zetner 1994b) and Ba (Li and Zetner 1994a, Zetner et al 1992, 1993.…”

Low energy superelastic scattering from the 41P1state of calcium in an (e, 2e) spectrometer

“…to fit to the data, where A is the offset, B is the amplitude of the sinusoidal function and C is the relative phase of the signal taken with respect to the incident electron beam direction. This function contrasts slightly with that used by Zetner and colleagues [16], who used a co-sinusoidal function with an argument of 2θ pol . It can be shown that by using this functional form in this geometry, the linear ACPs can be directly related to the parameters A, B and C which are obtained from a non-linear least squares fit to the data.…”

“…Since the majority of atomic targets have their first excited state above this range, the superelastic technique cannot be used and conventional electron-photon coincidence methods must be adopted. For this reason, the superelastic method has been constrained mostly to the alkali targets (see [8-15, 17, 18, 23-29, 33]), and more recently to the alkali-earth targets (see [16,[19][20][21][22][30][31][32]).…”

Electron impact on laser excited barium atoms

“…Second, inelastic scattering may lead to final states which are not accessible by dipole allowed synchrotron excitation. To our knowledge the combination of laser excitation and electron impact has been applied to barium only by very few laboratories: the JPL-group [10,11,12,13] investigated atomic levels below the first ionization threshold through elastic and superelastic collisions with electrons, while Bushaw et al [14] obtained electron impact ionization rates for 138Ba 6s6p 1P 1 by measuring the ion signals after collisions with slow electrons.…”