INITIAL AND FINAL ORBITAL ALIGNMENT PROBING OF THE FINE-STRUCTURE-CHANGING COLLISIONS AMONG THE CA(4S)(1)(4P)(1),(3)P(J) STATES WITH HE - DETERMINATION OF COHERENCE AND CONVENTIONAL CROSS-SECTIONS

A laser pump-probe experiment is used to study the orbital alignment e ffects, orientation effects and vector correlations of collisonal tran sfer of the Ca (4s)1(4p)1, P-3(1) state to the Ca (4s)1(4p)1, P-3(2, 0 ) levels. The experiment is configured in a single-collision crossed-b eam arrangement between Ca and He, and multi-structure cross-sections are determined using appropriate combinations of linear and circular l aser light for the pump/probe steps. Real and imaginary parts of coher ence cross-sections are obtained along with the conventional populatio n cross-sections for the m1 --> m2 magnetic sublevel transitions into the P-3(2) level. The total relative cross-section ratio for the perpe ndicular (m1 = +/- 1) to parallel (m1 = 0) polarization preparation of P-3(1) transferring to P-3(2) is 1.46 +/- 0.15. For initial P-3(1) pr eparation with laser light linearly polarized perpendicular to the ini tial relative velocity vector, the transfer into the m2-sublevels of t he P-3(2) state show a distinct preference for the sign-changing m1 = + 1 --> m2 = -1 transition. Preparation of Ca P-3(1) with laser light linearly polarized parallel to the initial relative velocity vector pr oduces population transfer into the P-3(2) level that is completely al igned in the +/- 1 and +/-2 sublevels, consistent with symmetry consid erations. The magnitudes of the coherence cross-sections range from a few percent to greater than 100% of some of the population transfer co nventional cross-sections. Study of the alignment effect into the fina l P-3(0) state found a very large observed effect (sigma(\m\=1)/sigma\ m\=0) of 23 +/- 0.9. Interpretation of the energy transfer results ind icates that the energy transfer obeys symmetry rules and follows predi ctions of curve crossings between the SIGMA and PI potentials, where f or the transfer into P-3(2) only indirect coupling can occur.