Electrons released from clusters through strong Xray pulses show broad kinetic-energy spectra, extending from the atomic excess energy down to the threshold, where usually a strong peak appears. These low-energy electrons are normally attributed to e
vaporation from the nano-plasma formed in the highly-charged clusters. Here, it is shown that also directly emitted photo electrons generate a pronounced spectral feature close to threshold. Furthermore, we give an analytical approximation for the direct photo-electron spectrum.
We investigate theoretically electron dynamics under a VUV attosecond pulse train which has a controlled phase delay with respect to an additional strong infrared laser field. Using the strong field approximation and the fact that the attosecond puls
e is short compared to the excited electron dynamics, we arrive at a minimal analytical model for the kinetic energy distribution of the electron as well as the photon absorption probability as a function of the phase delay between the fields. We analyze the dynamics in terms of electron wave packet replicas created by the attosecond pulses. The absorption probability shows strong modulations as a function of the phase delay for VUV photons of energy comparable to the binding energy of the electron, while for higher photon energies the absorption probability does not depend on the delay, in line with the experimental observations for helium and argon, respectively.
