PHOTODETACHMENT OF THE H- ION

Detachment of electrons from the H- ion is investigated with an experimental technique whereby an H- beam moving at a relativistic velocity (2.5 x 10(10) cm/s) is intersected with a fixed frequency laser. The Doppler effect allows systematic variation of the center-of-mass (CM) photon energy over a wide range (factor of 10) by simply adjusting the angle between the ion and laser beams. The focused output from a pulsed, linearly polarized, CO2 TEA laser operating at 10.6-mu-m, with peak intensities on the order of 10 GW/cm2, was used to examine the multiphoton absorption process in H-. The fourth harmonic (266 nm) of a Nd:YAG laser was used to investigate some of the doubly-excited state resonances in H-. In the multiphoton absorption work, electron detachment was observed at photon energies where as few as 2 and as many as 8 photons are required to get above the 1-electron detachment threshold (EDT) of H- (0.754 eV). Electron yield vs photon energy plots exhibit structure that is laser intensity dependent. Electron yield vs laser pulse energy data was obtained at a few selected CM wavelengths and laser pulse energies. In the single-photon UV laser work, numerous resonances within the H- photodetachment continuum corresponding to one-photon two-electron excitation processes were observed. The doubly-excited resonances appear to be of the Feshbach type. A simple, semi-empirical recursion formula predicts the resonance energy levels. The experimental techniques described here can be used to accurately determine accelerator beam and ion source parameters such as beam energy, energy-spread, and ion density spatial distribution.