IONIZATION OF RYDBERG WAVE-PACKETS BY SUBPICOSECOND, HALF-CYCLE ELECTROMAGNETIC PULSES

We have studied the ionization of Rydberg wave packets by subpicosecon d, nearly unipolar electromagnetic field pulses, in the regime where t he duration of the electric field is less than the classical Kepler or bit time 2 pi (n) over bar(3) for the wave packet. In contrast to the subpicosecond optical pulses, subpicosecond field pulses can ionize wa ve packets when the probability density near the inner turning point o f the Kepler orbit is low. The transfer of energy from the electromagn etic field to essentially free electrons demonstrates that the pulses are substantially shorter than one field cycle. Such ''half-cycle'' pu lses can track the wave packet throughout its orbit, in order to study wave packet trajectories or other processes at the quantum-classical boundary.