P. A. M. Gram

Atomic Physics with Relativistic Beams

The availability of a beam of H- ions with near-luminal velocity has enabled us to investigate photon-atom interactions at photon energies and electric field strengths presently beyond the scope of ordinary laboratory techniques. See Fig. 1. We have surveyed the entire photodetachment spectrum of H- from threshold for single electron detachment to well above the threshold for two-electron detachment. Embedded in the one-electron photodetachment continuum of H- are a series of doubly excited states, termed “resonances” since they are unstable against autodetachment into the continuum. The two most striking of these lie near the threshold for the production of H° (n = 2): a very narrow state just below the threshold, the “Feshbach” resonance, and a broader state lying just above the n = 2 threshold, the “shape” resonance. By means of Stark mixing, we have been able to use these 1P states to uncover nearby 1S and 1D states. Just below the threshold for H° (n = 3) production, we have found a prominent dip in the photodetachment cross section. This “Feshbach”-type state is accompanied by a narrower recursion lying between it and the n = 3 threshold. The single electron Open image in new window Fig. 40. We are studying a System moving with 84% the speed of light. Time is dilated and lengths are contracted by 1.853. photodetachment total cross section above n = 3 shows no further distinctive features upon examination with our current resolution, although there is some evidence for structure below n = 4.

Photodetachment of Relativistic Ions

A series of fundamental laser ion beam experiments has been made feasible by the high-quality, relativistic (ß = 0.842) H- ion beam available at the Clinton P. Anderson Meson Physics Facility (LAMPF). The relativistic Doppler shift of the light from an ordinary ultraviolet laser provides what is, in effect, a continuously tunable vacuum-ultraviolet laser in the rest frame of the moving ions. The Lorentz transformation of a modest laboratory magnetic field provides an electric field of several megavolts/centimeter. The latest results of our photo-detachment work with H- beams and our spectroscopic work with H0 beams are presented. Our plans for future work are discussed.