Exact Timing of Returned Molecular Wavepacket

An ionizing wavepacket of electron will re-visit its parent molecular ion during photoionization by strong laser field. This scenario is associated with physical concepts such as molecular re-scattering/collision, interference, diffraction, molecular clock, and generation of XUV light via high-order harmonic generation. On the workbench of a reduced dimensionality model of molecular hydrogen ions irradiated by laser pulse of 0.01-10.0 a.u. intensities, one-cycle pulsewidth, and 800nm wavelength, by deploying a momentum operator on the time-dependent wavefunction of an ionizing wavepacket, we can determine, in a precise manner, the exact time instant for the re-visiting electron to come back to the cation position. The time value is 57.6% of an optical cycle of the exciting laser pulse. This result may be useful in attosecond pump-probe experiments or molecular clock applications.     

Double-Exponentially Decayed Photoionization in CREI Effect： Numerical Experiment on 3D H2^＋

On the platform of the 3D H2^＋ system, we perform a numerical simulation of its photoionization rate under excitation of weak to intense laser intensities with varying pulse durations and wavelengths. A novel method is proposed for calculating the photoionization rate： a double exponential decay of ionization probability is best suited for fitting this rate. Confirmation of the well-documented charge-resonance-enhanced ionization （CREI） effect at medium laser intensity and finding of ionization saturation at high light intensity corroborate the robustness of the suggested double-exponential decay process. Surveying the spatial and temporal variations of electron wavefunctions uncovers a mechanism for the double-exponentially decayed photoionization probability as onset of electron ionization along extra degree of freedom. Henceforth, the new method makes clear the origins of peak features in photoionization rate versus internuclear separation. It is believed that this multi-exponentially decayed ionization mechanism is applicable to systems with more degrees of motion.