Attosecond pulse measurements and time delay in the ionization of Coulomb systems

Attosecond pulses are detected via atomic ionization and what we really measure strongly depends upon the short-time ionization dynamics. On the other hand, the latter is studied using ultrafast optical methods. We consider the time delay of electron detachment from a Coulomb center in the process of ionization. It is shown that the attosecond streaking, an ultrafast optical method most commonly used, can be formally described by placing a virtual detector of the arrival time delay at a certain distance from the center of the system. This allows derivation of a simple formula for Coulomb-laser coupling that perfectly agrees with the results of numerical solution of the appropriate time-dependent Schrödinger equation.