Attosecond photoionization for reconstruction of bound-electron wave packets

We present a method for the characterization of bound-electron wave packets generated by a broadband excitation pulse. The technique is based on the photoionization of the electron wave packet by a delayed isolated attosecond pulse and on the measurement of the ionization asymmetry parameter in the direction of the probe pulse polarization, which depends on the pump-probe delay and on the photoelectron energy. By numerically solving the fully three-dimensional time-dependent Schr¨odinger equation we show that Fourier analysis of the two-dimensional ionization asymmetry parameter, displaying a complex interference pattern, enables a clear observation of quantum beats between pairs of stationary states involved in the generation of the wave packet. An analytical model confirms that the quantum beats’ signal encodes the weight of each stationary state, thus suggesting a feasible approach for the complete characterization of the relative population ratio of the excited-state components of thewave packet. Moreover, an approach based on the further analysis of quantum beats is proposed to retrieve the lifetime added to each excited state.