The image on the cover for Advanced Photonics Volume 3, Issue 3, depicts tunneling ionization of an atom, as induced by a strong laser pulse. The complex hologram in the photoelectron momentum spectrum, which encodes rich structural and dynamic information of the atom, originates from the interference of the photoelectrons tunneling at different times during the laser pulse. By introducing a weak second harmonic field, the contributions of the photoelectrons tunneling at different times are identified, a significant step toward imaging the ultrafast dynamics in atoms and molecules with the photoelectron spectroscopy of tunneling ionization.

The image is based on original research by Jia Tan et al. presented in their paper “Resolving and weighing the quantum orbits in strong-field tunneling ionization,” Adv. Photon.3(3), 035001 (2021).