Space distribution of the rescattering electron wavepacket in the laser-atom interactions

We investigated the space distribution of the rescattering electron wavepacket created in the laser-atom interaction by a full quantum simulation and a semiclassical calculation. Both the quantum simulation and the semiclassical calculation showed that the rescattering electron beam current intensity can reach the order of 10 A/cm, much intense than the conventional electron beam. Different from the convention electron beam, the rescattering electron beam is of a non-uniform distribution both in energy and space. The simulated information is important for analyzing the molecular structure in the rescattering imaging experiments. The laser-material interaction is a hot research topics owing to the rapid advance of the laser technology. Most of the observed phenomena can be explained by the rescattering model proposed by Corkum [1]. The electron is firstly released by the laser through tunneling ionization when the laser field reaches its peak and the released electron is bounced back when the laser field changes the polarization direction. The collision of the bounced back electron with the parent core is similar to an electron beam incidents on the target. In principle, all the dynamics, which can be investigated by the conventional electron beam, can also be investigated with the rescattering electron beam. More attractively, the rescattering electron beam is a coherence beam and the beam intensity is much higher than the conventional one. Thus, the rescattering electron beam provides a potential way to image the molecular structure [2], like the conventional (e,2e) experiment [3]. For the conventional electron beam, the beam intensity, beam energy and so on can be controlled in the experiment. For the rescattering electron beam, the full information [4] about the rescattering beam, namely, the energy distribution and the space distribution, is unknown. Without such knowledge, the beam quality cannot be controlled experimentally. Since the rescattering is an intermediate process, the information cannot be obtained directly from the experimental measurement. It has to rely on the numerical simulation. In principle, all the dynamic information can be obtained by solving the time-dependent Schrödinger equation. In practice, directly getting the rescattering information is not easy because (1) the wavefunction corresponds to the tunneling ionized electron is just a small factional part of the total wavefunction; (2) the rescattering electron wavepackets created at different laser cycles mix up and so it is difficult to decompose the n-th returns clearly. Of course, The 8th Asian International Seminar on Atomic and Molecular Physics IOP Publishing Journal of Physics: Conference Series 185 (2009) 012048 doi:10.1088/1742-6596/185/1/012048 c © 2009 IOP Publishing Ltd 1 the rescattering information can be obtained by a semiclassical simulation [5] but the reliability of the classical results is not clear. In our previous work [6], we proposed a numerical procedure to obtain all the rescattering information directly by solving the time-integral equation instead of the differential Schrödinger equation and we extracted all the rescattering information. So far most of the works focused on the returning time and energy distribution, there is no report on the space distribution of the scattering electron, which is another crucial information for the molecular structure imaging study using rescattering electron beam. In this paper, we study the space distribution of the rescattering electron beam in a full quantum, nonperturbative method. Similar to our previous work [6], we rewrote the time-dependent Schrödinger equation into an integral equation and factored out the non-active part which corresponds to the initial state without interacting with the laser field. The time-dependent wavefunction is formally written as (atomic units h̄ = m = e = 1 are used)