Time resolved measurements of atomic photoionization are at the forefront of atomic and molecular physics. Recent experiments with ultra-short laser pulses show that the photoemission occurs on a finite time scale which is of the order of tens of attoseconds (1as = 10−18s). To resolve such a short time, the ionizing XUV laser pulse initiates the photoemission process and a probing IR pulse steers the photo-electron towards the detector. The time delay between the pump and probe pulses is converted to the photoelectron energy (attosecond streaking) or yield (RABBITT technique).
In this talk, I will cover basics of the attosecond streaking and RABBITT techniques which involve interaction of atoms with electromagnetic radiation at low or moderate intensities. The first part of the talk will cover XUV ionization and related approximations and will be followed by the description of two photon ionization processes. Theoretical description will be based on a time-dependent perturbation theory and reduction of the complex atomic system with N interacting electrons to one active electron. The influence of electron correlation on valence shell photoionization of noble gas atoms will also be reviewed.