Resonant two-photon ionization of helium atoms studied by attosecond interferometry

We study resonant two-photon ionization of helium atoms via the 1 s 3 p , 4 and 5 P states using 15 th harmonic a titanium-sapphire laser for excitation weak fraction field ionization. The phase photoelectron wavepackets is measured by an attosecond interferometric technique, 17 harmonic. perform experiments with angular resolution velocity map imaging spectrometer high energy magnetic bottle electron spectrometer. Our results are compared to calculations random approximation exchange account correlation effects. give interpretation multiple π -rad jumps observed, both at away from resonance, as well their dependence on emission angle.