Hole burning and higher-order photon effects in attosecond light-atom interaction

We have performed calculations of attosecond laser-atom interactions for laser intensities where interesting two- and three-photon effects become relevant. In particular, we examine the case of "hole burning" in the initial orbital. Hole burning is present when the laser-pulse duration is shorter than the classical radial period because the electron preferentially absorbs the photon near the nucleus. We also examine how the three-photon Raman process can lead to a time delay in the outgoing electron for the energy near one-photon absorption. For excitation out of the hydrogen 2s state, an intensity of 2.2×1016 W/cm2 leads to a 6-as delay of the outgoing electron. We argue that this delay is due to the hole burning in the initial state.