Photoionization dynamics and angular squeezing phenomenon in intense long-wavelength laser fields

We develop a coherent-state Ehrenfest trajectory (CSET) approach for the nonperturbative study of full electronic and nuclear dynamics of molecules interacting with intense laser fields. In this approach, electrons and nuclei are characterized by CSETs, dynamic processes are identified by the properties of the CSETs, and the transition probability of a process is calculated from the number of CSETs in this process. We apply this approach to simulate the full dynamics of H{sub 2} in intense linearly polarized laser fields. In the tunneling regime, the photoelectron energy spectra show a pronounced low-energy structure (LES) and the predicted scaling law of the LES with respect to the Keldysh parameter is in very good agreement with that observed in the latest experiments. Moreover, the photoelectron angular distribution is found to be squeezed along the laser field direction with the increase of laser wavelength and/or intensity.