Intense-field multiphoton ionization of a two-electron atom

Multiphoton ionization of helium at high laser intensities has been investigated by direct numerical integration of the full time-dependent two-electron Schrodinger equation on a Gray T3D. At held intensities above 4 x 10(14) W cm(-2), two-photon ionization occurs in a few field periods, and double ionization and high harmonic generation are prominent. We present calculations of double ionization yields, investigate the sensitivity of double ionization to the electron-electron electrostatic repulsion, and present evidence of unexpected non-exponential behaviour in ionization decay rates.