Multiphoton ionization of atomic hydrogen is investigated experimentally in the short-pulse regime (T< 0.5 ps) at wavelengths around 600 nm and intensities up to 10 14 W/cm 2 . 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 n >: 4 and / > 3. PACS numbers: 32.80.Fb, 32.80.Rm 2 4 57 1 1 II 1 1 II J
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.