A charged particle emits (absorbs) electromagnetic radiation efficiently in the region where its acceleration is at a maximum. In an atom this region is close to the nucleus, where the electron motion can be approximated by a parabola. Based on this approximation, Kramers (see Ref. [1]) has derived very simple and accurate expressions for the transition probabilities between hydrogenic bound-bound and bound-continuum states. This law has a more expressed manifestation in the multiphoton absorption process. The interaction of atoms with short electric pulses differs sharply from that for laser pulses. In recent years the ionisation of atoms in high-lying Rydberg states by unipolar so-called half-cycle pulses (HCP's) has been studied extensively. Here we discuss only the limit of a very short HCP whose duration r is much shorter than the classical electron orbital period T_K = 27πn~3, where E_n = - 1/2n~2 is the electron initial energy (atomic units are used throughout). In this limit, the HCP with the peak value FO delivers a momentum q = F_0τ to she electron. As shown in Ref., the large distances from the atomic core play an important role in the interaction of the HCP with a Rydberg atom, and states with a large angular momentum are involved in the process of HCP absorption. In this work, we consider the classical theory of the Rydberg atom kicked by one and two HCP's. On the basis of the semiclassical approximation, we derive also the expression for the atomic wave packet created by a short unipolar electric pulse.
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