Alignment and Orientation Effects in Sr Energy Pooling

Abstract

Alignment and orientation effects in the energy pooling process, Sr(5s5p 3P1) + Sr(5s5p 3P1) → Sr(5s5p 1P1) + Sr(5s2 1S0), are studied in a single atomic beam. The Sr atoms are prepared in an aligned initial state with a polarized laser, and alignment information is extracted by observing the fluorescence from the final Sr(5s5p 1P1) state as the atoms precess in an applied magnetic field. This allows the dependence of the total energy pooling cross section (integrated over the final state alignment) on the initial state alignment to be almost completely described. A prominent alignment effect is observed. If mj represents the component of total electronic angular momentum of a Sr(5s5p 3P1) atom along the relative velocity vector of the collision, then the total energy transfer cross section for a particular initial state alignment can be expressed as a sum of the so-called fundamental cross sections, σm1m2 and σm1m2;m1‘m2‘, that describe collisions between the various mj states. Here σm1m2 represents the cross section for energy transfer when an atom in state m1 collides with an atom in state m2. The cross section σm1m2;m1‘m2‘ represents the contribution to the total cross section from interference when the colliding system is in a superposition of the state m1 colliding with m2 and the state m1‘ colliding with m2‘. It is found that the cross sections σ1-1, σ00, and σ10 as well as the interference terms Re(σ00;1-1) and σ01;10 have relatively large values while σ11 and σ1-1;-11 are small. Coupled with future theoretical work, these results may provide new insights into the dynamics of the curve crossings that lead to energy transfer.