In this presentation, I will talk about a semiclassical model to capture the details of above threshold ionization of atoms and molecules in elliptically and linearly polarized laser fields. Experimentally, we have measured photoelectron angular distributions (PADs) with high resolution for multiphoton ionization of rare gas atoms in infrared laser fields. Based on the Ammosov-Delone-Krainov (ADK) tunneling theory, we develop an intuitive quantum-trajectory Monte Carlo (QTMC) model encoded with Feynman's path-integral approach, in which the Coulomb effect on electron trajectories and interference patterns are fully considered. Considering the molecular orbital structure, we have extended the model for strong-field tunneling ionization of molecules. We extract the phase structure of the tunneling wavepackets and discuss its effect on the photoelectron momentum distributions of the aligned molecules. The theory has a general application of photoelectron holography, molecular orbital imaging etc.
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