Coherent Control of Molecular Ion Production in Cold Rb Vapor

D. Gerlich

M. L. Trachy, G. Veshapidze, M. H. Shah +2 more

We explore 2-color photoassociative ionization in cold Rb vapor and present experimental evidence that the molecular ions are produced from the stepwise excitation of a ladder of molecular states. We also explore a new process, dubbed photoassociative-dissociative ionization, by which atomic ions are created by excitation through a ladder of molecular states, finally autoionizing to a dissociative potential curve of Rb2+. We submit that these experiments could be the starting point for the same sort of high resolution spectroscopy that has already been done for lower electronic states of cold Rb2 at large internuclear separation.

G. ten Haaf

G. Veshapidze, M. L. Trachy, Hyounguk Jang +2 more

Ultrafast and narrow linewidth lasers are combined to study multiphoton photoassociative ionization (PAI) in a Rb magneto-optical trap. Through the use of time of flight spectroscopy and by varying the parameters of the ultrafast laser, the excitation pathway for PAI was determined. It was found that ${{\mathrm{Rb}}_{2}}^{+}$ is formed, not by direct photoionization, but by sequential excitation of ${\mathrm{Rb}}_{2}$ to an autoionizing state. Determining the excitation and ionization pathway was a necessary first step for future efforts in trying to establish coherent control techniques, first for the efficient production of translationally cold ${\mathrm{Rb}}_{2}$, and then for transferring population to a desired vibrationally cold molecular state.

Alexander Dörfler

This thesis explores the fundamental physical and chemical processes between molecular ions and neutral atoms in the gas phase at very low energies. At temperatures in the mK regime, these are dominated by long-range interactions and only a few partial waves. This study contributes to the understanding of the details of intermolecular interactions and provides valuable data for benchmarking theoretical models and quantum-chemical calculations. Although there is a wide range of previous atomic collision system studies, the investigations of cold collisions with molecular ions are limited. The experimental setup used in this work enabled the measurement of rate coefficients for molecular ion-neutral collisions. The development of a dynamic ion-neutral hybrid trap with improved control over collision energy led to new insights into charge-transfer rate coefficients for molecular ion-neutral atom collisions involving N$^+_2$+Rb, O$^+_2$+Rb and N$_2$H$^+$+Rb. Two different experimental settings enable state-and collision-energy dependent measurements of rate coefficients for all systems revealing an intriguing interplay between long-and short-range effects for the homonuclear diatomics by comparison to theoretical calculations and surprising experimental results for the polyatomic study. A fit of a constant function to the measured CT rate coefficients in the state-dependent experiment of N$_2$H$^+$+Rb yielded the similar result as for N$^+_2$+Rb($5s$)($^2S_{1/2}$). In the collision-energy dependent experiment the CT rate coefficient for N$_2$H$^+$+Rb($5s$)($^2S_{1/2}$) and N$_2$H$^+$+Rb($5p$)($^2P_{3/2}$) are both similar to the results for N$^+_2$+Rb($5s$)($^2S_{1/2}$), and also the rate coefficients increase as the collision-energy increases.

Brian Kaufman, Philipp Marquetand, Tamás Rozgonyi +1 more