Predicting intense-field photoionization of atoms and molecules from their linear photoabsorption spectra in the ionization continuum

We report a new approach to intense-field photoionization that is based on the ad hoc assumption that m photons of energy E-ph arriving within a typical electronic response time are effectively equivalent to a single photon of energy mE(ph). The heuristic model contains no adjustable parameters and unifies apparent multiphoton and field aspects. Moreover, nonsequential, suppressed and above-threshold ionization phenomena become readily understandable. Predicted ionization intensities are in satisfactory agreement with available experimental data ranging from C6H6 to Ne3+ from femtosecond to nanosecond laser pulses, and from ultraviolet to infrared. laser radiation.