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 effects, orientation effects and vector correlations of collisonal transfer 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-beam arrangement between Ca and He, and multi-structure cross-sections are determined using appropriate combinations of linear and circular laser light for the pump/probe steps. Real and imaginary parts of coherence cross-sections are obtained along with the conventional population cross-sections for the m1 --> m2 magnetic sublevel transitions into the P-3(2) level. The total relative cross-section ratio for the perpendicular (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) preparation with laser light linearly polarized perpendicular to the initial relative velocity vector, the transfer into the m2-sublevels of the 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 produces population transfer into the P-3(2) level that is completely aligned in the +/- 1 and +/-2 sublevels, consistent with symmetry considerations. The magnitudes of the coherence cross-sections range from a few percent to greater than 100% of some of the population transfer conventional cross-sections. Study of the alignment effect into the final 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 indicates that the energy transfer obeys symmetry rules and follows predictions of curve crossings between the SIGMA and PI potentials, where for the transfer into P-3(2) only indirect coupling can occur.