Ionization of multielectron systems is investigated by using one-dimensional, multiconfiguration time-dependent Hartree-Fock calculations. Our analysis reveals the key physical processes underlying ionization of complex systems. The laser-induced multielectron dynamics, and therewith the ionization process, depend on the ratio of laser frequency $\left({\omega }_0\right)$ to plasmon frequency $\left({\omega }_p\right)$. In the overresonant limit $({\omega }_0⪢{\omega }_p)$, tunnel ionization is destroyed and ionization takes place by a classical over the barrier mechanism. In the underresonant regime $({\omega }_0⪡{\omega }_p)$, tunnel ionization remains dominant, but is weakened by a polarization-induced growth of the tunneling barrier.

• Received 28 June 2004

DOI:https://doi.org/10.1103/PhysRevA.70.041401