MULTIPHOTON IONIZATION OF ATOMIC-HYDROGEN IN INTENSE SUBPICOSECOND LASER-PULSES

Multiphoton ionization of atomic hydrogen is investigated experimentally in the short-pulse regime (0.5 ps) at wavelengths around 600 nm and intensities up to 1014 W/cm2. Sharp peaks in the energy spectrum of the photoelectrons can be attributed to resonant ionization processes via excited states which are ac-Stark shifted into resonance. Energies and angular distributions of the electrons allow one to identify some participating excited states with quantum numbers n4 and l3. © 1990 The American Physical Society.