Attosecond ionization dynamics of modulated, few-cycle XUV pulses

Few-cycle, attosecond extreme ultraviolet (XUV) pulses in the strong field regime are becoming experimentally feasible, prompting theoretical investigating of the ionization dynamics induced by such pulses. Here, we provide a systematic study of the atomic ionization dynamics beyond the regime of the slowly varying envelope approximation. We discuss the properties of such XUV pulses and report on temporal and spectral modulations unique to the attosecond nature of the pulse. By employing different levels of theory, namely the numerical solution to the time-dependent Schrödinger equation, perturbation theory and a semi-analytical approach, we investigate the ionization of atoms by modulated, few-cycle XUV pulses and distinguish first and higher order effects. In particular, we study attosecond ionization in different intensity regimes aided by a general wave function splitting algorithm. Our results show that polarization and interference effects in the continuum prominently drive ionization in the few-cycle regime and report on carrier-envelope phase (CEP)- and intensity-dependent asymmetries in the photoelectron spectra. The use of spectrally modulated attosecond pulses allows us to distinguish between temporal effects causing asymmetries and dynamic interference, and spectral effects inducing a redshift of the photoelectron spectrum.