  We study the photoionization and autoionization of Helium atom subject to
ultrashort laser pulses by using a Feshbach formalism in the time domain. We
solve the time-dependent Schr\"odinger equation in terms of a configuration
interaction (CI) spectral method, in which the total wavefunction is expanded
with configurations defined within bound-like ($\mathcal{Q}$) and
scattering-like ($\mathcal{P}$) halfspaces. The method allowsone to provide
accurate descriptions of both the atomic structure (energy positions and
widths) and the photodynamics. We illustrate our approach by i) calculating the
time-resolved one-photon ionization below the He$^+$ ($n$=2) ionization
threshold, from $1^1S^e$ and $2 ^1P^o$ initial states, then reaching the lowest
autoionizing states of $^1S^e$, $^1P^o$ and $^1D^e$ final symmetries ii)
studing the temporal formation of the Fano profile of $^1P^o$ resonances and
iii) showing its performance in obtaining the perturbative long-time limit of
one- and two-photon ionization cross sections using ultrashort laser pulses
following a recently developed procedure in Phys. Rev. A, {\bf 77}, 032716
(2008).

Atomic Physics;Quantum Physics