Kinetic energy distribution of the rescattering electrons from asymmetric $\omega$/2$\omega$ pulses

Abstract

When high intensity pulses are used to ionize an atom or molecule, the electrons produced can be driven back to the ionic core by the laser’s electric field, where they can collide with the ion, resulting to a plethora of phenomena such as high harmonic generation, non-sequential double ionization and more. Here, we consider ionization using an asymmetric $\omega$/2$\omega$ pulse, and we study the dependence of the kinetic energy distribution of the returning electrons on the relative phase $\phi$ and electric field amplitude ratio $\gamma$ between the two components of the asymmetric pulse. We find that for a specific combination of $\gamma$ and $\phi$, the kinetic energy of the vast majority of the returning electrons which return to the ion, follows a sharp, nearly monochromatic distribution. We examine the effect of small variations of the asymmetric pulse parameters $\gamma$ and $\phi$, as well as the effect of pulse duration and multiple returns of the electron to the ionic core. We find that the kinetic energy distribution remains narrow for a variety of such conditions, demonstrating the experimental feasibility of the process. This way, $\omega$/2$\omega$ asymmetric pulses can offer control over a variety of rescattering-related processes, such as high-harmonic generation, for which we give an example.

Graphical abstract

(a) Evolution of the kinetic energy distribution of the returning electrons as a function of the phase $\phi$ between the $\omega$ and 2$\omega$ components of the asymmetric field. The amplitude ratio $\gamma$ between the $\omega$ and 2$\omega$ components of the asymmetric field is 0.45. (b) Evolution of the HHG spectra as a function of $\phi$. The ratio $\gamma$ is 0.45 as in part (a)