Strong-Field Ionization in Bicircular Laser Fields

We ordinarily take Einstein's description of the photoelectric effect to mean that atoms can absorb only one photon at a time, thereby prohibiting ionization by weak, low-frequency light. But shortly after the invention of the laser, it was found that under intense illumination, atoms could simultaneously absorb many photons, leading to so-called multiphoton ionization. It was also discovered that a second electron could be liberated with surprising efficiency through a process known as rescattering, where the first electron is driven back to the ion leading to impact double ionization. Since this process relies on trajectories that bring the first electron back to the parent ion, it is most effective with linear polarization and absent with circular polarization. But there has recently been great interest in ionization dynamics driven by intense bicircular light, generated by combining two colors of circularly polarized light. Here we present new results using a classical ensemble approach and utilizing a high-performance computational cluster. We uncover novel patterns in recollision timing, identify classes of complex trajectories that contribute to double ionization, and map various ionization processes onto the resulting transverse electron momentum distributions.