ATOMIC-HYDROGEN IN A STRONG OPTICAL RADIATION-FIELD

Experimental energy spectra and energy-resolved angular distributions of photoelectrons produced by multiphoton ionization of atomic hydroge n are presented for several wavelengths between 596 and 630 nm, peak i ntensities of about 10(14) W/CM2, and laser pulse durations of about 0 .5 ps. Resonant ionization processes via ac Stark-shift-induced resona nces with excited states dominate the spectra. The results of Sturmian -Floquet calculations of these spectra and angular distributions are p resented; they are in fair agreement with the experimental data.