Electronic rescattering dynamics in intense few-cycle laser fields (Vol. 43 No. 3)

The interaction of intense laser fields with atoms gives rise to characteristic strong-field effects, most notably above-threshold ionization and high-harmonic generation. After the electron tunnels out of the atomic potential, it is accelerated by the laser field before being driven back to the parent ion by the same field. The returning electron energy ranges from a few to a few hundred eV depending on the field parameters. Upon rescattering, parts of the electron wave-packet may recombine with the atom under emission of energetic radiation of harmonics of the laser frequency. The harmonic radiation carries characteristics of the atomic potential, as well as of the rescattering electron. This sequence of processes can be directly visualized by a quantum phase space analysis. Using a Wigner phase-space distribution, one can relate the coordinate-momentum space distribution of the returning electron to the temporal emission pattern of the harmonic spectrum (see Figure).

Such relation between the time-frequency vs. the coordinate-momentum space distribution has been calculated for different atomic model potentials, the Coulomb potential supporting a Rydberg series and short-range potentials, with a finite number of bound states. The important role of dynamic bound-state polarization effects in the harmonic emission can be identified. The long-range part of the Coulomb spectrum modifies the local momentum distribution at the moment of rescattering. This might become important for an improved description of experiments aiming towards a tomographic reconstruction of the electronic structure of a system using the harmonic spectrum.