We study resonant two-color two-photon ionization of helium via the 1s3p P11 state. The first color is the 15th harmonic of a tunable Ti:sapphire laser, while the second color is the fundamental laser radiation. Our method uses phase-locked high-order harmonics to determine the phase of the two-photon process by interferometry. The measurement of the two-photon ionization phase variation as a function of detuning from the resonance and intensity of the dressing field allows us to determine the intensity dependence of the transition energy. © 2010 The American Physical Society.
Publication Source (Journal or Book title)
Physical Review Letters
Swoboda, M., Fordell, T., Klünder, K., Dahlström, J., Miranda, M., Buth, C., Schafer, K., Mauritsson, J., L'Huillier, A., & Gisselbrecht, M. (2010). Phase measurement of resonant two-photon ionization in helium. Physical Review Letters, 104 (10) https://doi.org/10.1103/PhysRevLett.104.103003