Photoassociation and Rovibrational Cooling of Sodium Cesium Using Chirped Laser Pulses and Stimulated Raman Adiabatic Passage

Abstract

This dissertation presents the study of how two laser pulses can bind sodium and cesium atoms at ultracold temperature ($T=200\mu K$) into an ultracold, polar, diatomic molecule with a definite quantum state. A single-channel scattering model represents the initial continuum state, and two different models represent the intermediate state: one excluding spin-orbit coupling effects in the intermediate state, the other accounting for such effects. We calculate the $A^1\Sigma^+-b^3\Pi$ spin-orbit coupled wave functions using a basis expansion technique, and validate the results by comparing to experimentally obtained, spin-orbit coupled energy levels. The computation of photoassociation rates between the continuum state and the intermediate states reveals the crucial importance of spin-orbit coupling. Furthermore, this study shows how the spectral bandwidth (narrow \vs broad), the chirping (chirped vs. unchirped), the detunings, the intensities, and the pulse delay (intuitive \vs counter-intuitive sequence) of the lasers affect the transfer of population from the continuum scattering state to a comparatively low-lying ($v_X=32, J_X=0$) rovibrational state of the $X^1\Sigma^+$ ground electronic state of NaCs. The transfer process relies either on a sequence of $\pi$-pulses, or uses stimulated Raman adiabatic passage (STIRAP). Lasers with narrow spectral bandwidth ($0.5\GHz$) always yield a final population in $\ket{X^1\Sigma^+, v_X=32, J_X=0}$ higher than 95% in less than 4 ns.