Observation of multiphoton detachment of theH−ion

We have observed nonresonant multiphoton electron detachment of ${\mathrm{H}}^{\mathrm{-}}$ ions in moderately intense (a few tens of GW/${\mathrm{cm}}^2$) laser fields. A well-collimated beam of ${\mathrm{H}}^{\mathrm{-}}$ ions with an energy of 581 MeV was intersected by focused 10.6-μm radiation from a pulsed ${\mathrm{CO}}_2$ laser. The center-of-mass photon energy was tuned using the relativistic Doppler shift so that the minimum number of simultaneous photons required for electron detachment ranged from three to sixteen. Definite signals were observed for the minimum photon number ranging from three to eight. Our preliminary results show evidence for structure in the relative total cross section.