Three-photon ionization of He/sup +/ by the 13th harmonic of a Ti:sapphire laser

In this study, numerical experiments of three-photon ionization of He/sup +/ are performed. He/sup +/ is chosen over He because it is easy to prepare (by optical field ionization) and its 1s - 2s transition (40.8 eV) is close to the two-photon resonance of the 13th harmonics of a Ti:sapphire laser. Moreover, the exact solution can be delivered for this hydrogenlike system. We solve the time-dependent Schrodinger equation numerically using the Peaceman-Rachford method. Results show that this process is an attractive candidate for the observation of a third-order nonlinear optical effect and even above-threshold ionization in the XUV range.