Electric Field Ionization of Highly Excited Rubidium Atoms

Nathan I. Hammer, R. N. Compton

Daniel I. Khomskii

G. B. McMillian

A frequency stabilized ring dye laser, with a linewidth of (TURN)250 kHz, has been utilized to selectively excite Rb(N('2)S, N('2)D) states in the range N = 20 - 100 by a two photon process. The highly excited atoms were detected by the technique of electric field ionization. Excited states with (VBAR)M(,L)(VBAR) < 3 have been observed to ionize along predominantly adiabatic paths and states with (VBAR)M(,L)(VBAR) (GREATERTHEQ) 3 have been observed to ionize along predominantly diabatic paths for the range of N investigated. The electric field dependence of the ionization threshold has been determined to be in good agreement with that calculated from a simple model based on the energies and ionization rates of hydrogen.\nCollisions between highly excited rubidium atoms and neutral xenon atoms, which result in a change in the N and L of the excited state of the rubidium atom, have been investigated. The N of the final state has been shown to be limited to those states which lie closest in energy to the initial state, in good agreement with theory. The distribution of L of the final states has been shown to be completely statistical or biased towards production of high L. The distribution of final L is definitely not biased toward production of states with low values of L.

悟 山田

M. Chéret, L. Barbier, W. Lindinger +1 more

Nathan I. Hammer

Multiphoton ionization (MPI) of rubidium atoms at both low (atomic beam) and high (heat pipe) densities is studied using a tunable OPO laser. At high Rb densities ionization of the laser excited ns, np, and nd states occurs both through photoionization and collisional ionization. Excitation of the np states is found to be induced by the external electric field at both low and high densities. In addition, np signal is also seen at very low (E→0) fields in the heat pipe, providing evidence for collision mixing as well as field mixing. At low densities, signal for the high np states initially increases with applied field, but soon saturates (i.e. becomes field independent) while the signal for high nd states decreases with increasing field. At low Rb densities strong resonance features are observed in the energy region between the zero field limit (IP) and the field ionization limit. These features, as well as the field ionization threshold, are found to be dependent upon the angle between the laser polarization and the direction of the applied dc field. Evidence for tunneling through the barrier created by the −e2/r−eEr potential is also presented for ns and nd states.