We have measured and calculated electron-impact excitation cross sections from the laser-excited Yb (. . . 6s6p 3 P 1 ) level to the higher-lying Yb (. . . 6s6p 1 P 1 ), (. . . 6s5d 3 D 1,2,3 ) and (. . . 6s7s 3 S 1 ) levels at 20 eV impact energy. Measurements were performed using a crossed-beam apparatus, with resonant laser radiation incident on the electron-atom interaction region, providing excited-state atomic targets. Calculations were performed in the relativistic convergent close-coupling (RCCC), convergent close-coupling (CCC), and relativistic distorted-wave (RDW) approximations. We present measured and calculated partial differential cross sections (PDCS), which relate to differential cross sections and electron-impact coherence parameters through the target state anisotropy introduced by the laser geometry. Using theoretical predictions of the h electron-impact coherence parameter, we present the differential cross section for the 3 P 1 -3 S 1 excitation.
We have measured and calculated the P 3 collision Stokes parameter for electron-impact collisional de-excitation to the ytterbium (. . . 6s6p 3 P 1 ) level from the higher-lying 1 P 1 , 3 D 1,2,3 and 3 S 1 levels for 20 eV residual energy. These processes are the time-reverse of the experimentally measured processes, where an impact energy of 20 eV was used to collisionally excite the 3 P 1 target, prepared by resonant laser pumping. Measurements were performed using a crossed-beam apparatus, where excited-state atomic targets were produced using resonant laser radiation incident on the electron-atom interaction region. Calculations were performed in the relativistic convergent close-coupling , convergent close-coupling and relativistic distorted-wave approximations. The theoretical calculations show that the h electron-impact coherence parameter (EICP) is equal to 1/2, independent of the scattering angle. We use this result to present the L ⊥ EICP for the (. . . 6s7s 3 S 1 )→(. . . 6s6p 3 P 1 ) collision process.
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