RYDBERG ATOMS IN FAR-INFRARED RADIATION-FIELDS - II - WAVE-PACKET DYNAMICS

The short-pulse dynamics of excitation and stimulated emission between highly excited states (15<n <60) is studied with picosecond far-infra red pulses (40-60 mu m) originating from a free electron laser. We mea sured the excitation of a Rydberg wave packet in rubidium around n=40 excited from a deeper bound (n approximate to 20) Rydberg state by a p icosecond far-infrared laser pulse. Moreover, starting from a stationa ry n=40 state we found that upon irradiating with a short far-infrared laser pulse, adjacent Rydberg states are populated by resonant Raman transfer via a deeper (n = 20) bound state. Finally, we discuss the dy namics of wave-packet excitation at a Cooper minimum in lithium, where sign change of the excitation matrix elements causes excitation at la rge distances from the atomic core. Possible measurement methods for t his effect are discussed and found to yield different information.