Multiphoton ionization of a three-electron atom: Studies with 25-keV Al beams

An alternative technique to obtain neutral-atom beams for multiphoton-ionization studies, via wavelength-selective photodetachment of negative ions, is described. This approach is illustrated by multiphoton ionization of Al(3s23p 2P) atoms with selected visible and uv laser pulses of ≤300 ps duration, and with intensities ∼109–6×1010 W/cm2. For visible wavelengths, single-electron ionization dominates, while excitation of doubly excited states over the ionization limit is observed under uv irradiation. Possible future experiments and the general perspectives of the technique are briefly discussed.