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-infrared pulses (40-60 mu m) originating from a free electron laser. We measured 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 picosecond far-infrared laser pulse. Moreover, starting from a stationary 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 dynamics of wave-packet excitation at a Cooper minimum in lithium, where sign change of the excitation matrix elements causes excitation at large distances from the atomic core. Possible measurement methods for this effect are discussed and found to yield different information.