Diagrammatic approach to attosecond delays in photoionization. Phys

We study laser-assisted photoionization by attosecond pulses using a time-independent formalism based on diagrammatic many-body pertur-bation theory. Our aim is to provide an ab inito route to the “delays” for this above-threshold ionization process, which is essential for a quan-titative understanding of attosecond metrology. We present correction curves for characterization schemes of attosecond pulses, such as “streak-ing”, that account for the delayed atomic response in ionization from neon and argon. We also verify that photoelectron delays from many-electron atoms can be measured using similar schemes if, instead, the so-called continuum–continuum delay is subtracted. Our method is general and it can be extended also to more complex systems and additional correlation effects can be introduced systematically. 1 a