FEMTOSECOND TIME-RESOLVED OBSERVATION OF ABOVE-THRESHOLD IONIZATION IN NA-2

Femtosecond pump-probe techniques are applied to the measurement of ab ove-threshold ionization (ATI) electrons to observe the influence of v ibrational wave-packet dynamics on molecular above threshold ionizatio n in real time. When ionized by a single laser pulse structural change s in the ATI electron spectra map the changes of the vibrational wave- packet evolution in the resonant intermediate electronic states as a f unction of laser intensity. Molecular vibrational motion in the cohere ntly coupled electronic states dominates the electron energy distribut ion rather than the energy splitting induced by Rabi oscillations.