Dynamic resonances in the multiphoton ionization of Argon

We present results of wavepacket simulations for multiphoton ionization in Argon. The single-active-electron model is applied to estimate the single-electron ionization rates by λ = 390nm light with intensities up to I = 2 x 1014 W cm-2. The photoelectron spectrum is analysed to identify resonant energy levels and orbital symmetries for these wavelengths and intensities. The ionization rates are compared with R-matrix Floquet calculations and found to be in good agreement. We compare the fraction of low-energy and high-energy photoelectron yield to test the extrapolation of tunneling theory results recently reported. We find that our results at λ = 390nm and λ = 780nm are consistent with the extension of the tunnelling model into the multiphoton regime. For few-cycle intense pulses we find the signature of dynamic mixing of resonances in the low-energy photoelectron spectrum.