Abstract

We have observed that the amount of photoionization from an atomic Rydberg state with a pulsed laser depends critically on the length of the pulse, whereas lowest order perturbation theory implies that the yield only depends on the fluence (the integrated intensity) of the pulse. We have measured the yield for one-photon ionization with short (0.3 to 2.7 ps), high-intensity laser pulses from the 27d Rydberg state in barium. With equal fluence, the yield decreases for pulses shorter than the Kepler orbit time of the outer electron (2.2 ps), as not all of its wavefunction comes near the core during the length of the pulse. The observations and this classical picture are confirmed by quantum mechanical calculations.

© 1994 Optical Society of America