s-wave photodetachment from S- ions in a static electric field

Photodetachment from negative S ions has been studied in external electric fields up to 220 V/cm for laser polarization parallel to the electric field direction. Fast neutrals produced by a pulsed laser beam crossed with a 4 keV S - ion beam were detected to measure the relative cross sections. Increased ion currents, lower background signals, analog detection methods, and more precise wavelength calibration have produced higher quality data than previous direct cross-section ratio measurements on nonhydrogenic ions. The ratio of the electric field-on to electric field-off cross sections is found to be in excellent agreement with theoretical predictions, thus resolving a long-standing discrepancy with previous, less definitive experiments. As predicted, electron wave-function rescattering effects are very small in both the amplitude and the phase of the electric-field-induced oscillations.