Libin Fu

Scaling Laws of the Two-Electron Sum-Energy Spectrum in Strong-Field Double Ionization

The sum-energy spectrum of two correlated electrons emitted in nonsequential strong-field double ionization (SFDI) of Ar was studied for intensities of 0.3 to 2×10^{14} W/cm^{2}. We find the mean sum energy, the maximum of the distributions as well as the high-energy tail of the scaled (to the ponderomotive energy) spectra increase with decreasing intensity below the recollision threshold (BRT). At higher intensities the spectra collapse into a single distribution. This behavior can be well explained within a semiclassical model providing clear evidence of the importance of multiple recollisions in the BRT regime. Here, ultrafast thermalization between both electrons is found occurring within three optical cycles only and leaving its clear footprint in the sum-energy spectra.

Coulomb rescattering in nondipole interaction of atoms with intense laser fields

We investigate the ionization dynamics of atoms irradiated by an intense laser field using a semiclassical model that includes magnetic Lorentz force in the rescattering process. We find that the electrons tunneled with different initial transverse momenta (i.e., perpendicular to the instantaneous electric field direction) distributed on a specific circle in the momentum plane can finally converge to the same transverse momentum after experiencing Coulomb forward scattering. These electron trajectories lead to a bright spot structure in the two-dimensional transverse momentum distribution, and particularly in the long-wavelength limit, a nonzero momentum peak in the direction antiparallel to the laser propagation (or radiation pressure) direction. By analyzing the subcycle dynamics of rescattering trajectories, we unveil the underlying mechanism of the anti-intuitive peak. Beyond the strong-field approximation and the dipole approximation, we quantitatively predict the spot center and the peak position. Our results are compared with a recent experiment and some theoretical predictions are given.