Ionization of hydrogen atoms in attosecond pulse trains and strong infrared laser pulses

Ionization of a hydrogen atom exposed to an attosecond pulse train and a few-cycle middle infrared (MIR) pulse is calculated with the strong field approximation. The ionization events initiated by two attosecond pulses in the train are streaked in the presence of a weak MIR pulse, making the two ionization events overlap or separate in momentum representation. By changing the weak MIR pulse intensity, the interference structure in the photoelectron momentum distribution can be precisely tailored. When the MIR field is strong enough to produce substantial ionization, the overlapped attosecond pulse train and MIR field trigger the XUV-phase-dependent photoelectron angular distribution. Either the interference pattern or the angular distribution can be used to extract the carrier envelope phase of attosecond pulses, which makes it possible to visualize the sub-XUV-cycle dynamics.