Laser-assisted-autoionization dynamics of helium resonances with single attosecond pulses

Abstract

The strong coupling between two autoionizing states in helium is studied theoretically with the pump-probe scheme. An isolated 100-as XUV pulse is used to excite helium near the $2s2p{(}^{1}\phantom{\rule{0.16em}{0ex}}P)$ resonance state in the presence of an intense infrared (IR) laser. The laser field introduces strong coupling between $2s2p{(}^{1}\phantom{\rule{0.16em}{0ex}}P)$ and $2{p}^{2}{(}^{1}\phantom{\rule{0.16em}{0ex}}S)$ states. The IR also can ionize helium from both autoionizing states. By changing the time delay between the XUV and the IR pulses, we investigated the photoelectron spectra near the two resonances. The results are used to explain the recent experiment by Gilbertson et al. [Phys. Rev. Lett. 105, 263003 (2010)]. Using the same isolated attosecond pulse and a 540-nm laser, we also investigate the strong coupling between $2s2p{(}^{1}\phantom{\rule{0.16em}{0ex}}P)$ and $2{s}^{2}{(}^{1}\phantom{\rule{0.16em}{0ex}}S)$ by examining how the photoelectron spectra are modified versus the time delay and the possibility of observing Autler-Townes doublet in such experiments.