Model for describing resonance-enhanced strong-field ionization with shaped ultrafast laser pulses

We present a simple model for calculating strong-field atomic and molecular ionization dominated by Freeman resonances. Our model combines multiphoton coupling between bound states, including dynamic Stark shifts, with coupling to a discretized continuum. The simplicity of the model allows us to interpret pulse-shape-dependent strong-field ionization yields and to demonstrate the relevance of strong-field atomic or molecular phase matching to ionization, as well as bound-state population transfer. Comparison with experimental measurements demonstrates that the calculations capture the essence of the pulse-shape-dependent ionization yields.