Electron impact coherence parameters for the (...6s5d 1D2) to (...6s6p 1P1) excitation in 13Ba determined by superelastic scattering measurements

Superelastic electron scattering involving the de-excitation of laser-excited 138Ba (...6s6p1P1) to the lower-lying (...6s5d1D2) metastable level has been investigated. These measurements have been used to extract the electron impact coherence parameters which describe excitation out of an isotropic (...6s5d1D2) level to the higher-lying (...6s6p1P1) state. Studies have been carried out for an electron impact energy of 20 eV and a range of scattering angles up to 45o. This investigation represents a significant extension of coherence parameter measurements to inelastic transitions between excited atomic levels. (author)