  Coherent, broadband pulses of extreme ultraviolet (XUV) light provide a new
and exciting tool for exploring attosecond electron dynamics. Using
photoelectron streaking, interferometric spectrograms can be generated that
contain a wealth of information about the phase properties of the
photoionization process. If properly retrieved, this phase information reveals
attosecond dynamics during photoelectron emission such as multielectron
dynamics and resonance processes. However, until now, the full retrieval of the
continuous electron wavepacket phase from isolated attosecond pulses has
remained challenging. Here, after elucidating key approximations and
limitations that hinder one from extracting the coherent electron wavepacket
dynamics using available retrieval algorithms, we present a new method called
Absolute Complex Dipole transmission matrix element reConstruction (ACDC). We
apply the ACDC method to experimental spectrograms to resolve the phase and
group delay difference between photoelectrons emitted from Ne and Ar. Our
results reveal subtle dynamics in this group delay difference of photoelectrons
emitted form Ar. These group delay dynamics were not resolvable with prior
methods that were only able to extract phase information at discrete energy
levels, emphasizing the importance of a complete and continuous phase retrieval
technique such as ACDC. Here we also make this new ACDC retrieval algorithm
available with appropriate citation in return.
