Non-Adiabatic Atomic Transitions: Computational Cross Section Calculations of Alkali Metal-Noble Gas Collisions

Diode Pumped Alkali Lasers operate by exciting a gaseous cell of alkali metal to its P(3/2) excited energy state. A noble gas, present in the cell, collisionally de-excites the alkali metal to its P(1/2) state. The alkali atoms then relax to their S(1/2) ground state by emitting photons. The non-radiative de-excitation due to inert gas atoms represents an interesting juncture for DPALs operation. This process must be faster than the radiative relaxation back to the S(1/2) state for lasing to occur. The rate of non-radiative de-excitation is related to the collisional cross section and the cross section is related to the S-Matrix. A time-dependent algorithm, the Channel Packet Method, was implemented to predict S-Matrix elements for alkali metal - noble gas (MNg) collisions. The S-Matrix contains the close-coupled Hamiltonian of the MNg system in body-fixed coordinates represented in the P-Manifold of states. There were two major state-to-state coupling phenomena responsible for intramultiplet mixing: spin-orbit and Coriolis. A total of nine collisions were computationally simulated between Potassium, Rubidium, and Cesium and the noble gases Helium, Neon, and Argon. Temperature averaged cross-sections were calculated for the P(1/2) to P(3/2) transition and compared to experiment. The original document contains color images.