Phase Measurement of Resonant Two-Photon Ionization in Helium

Authors :: Swoboda, M.
Fordell, T.
Klünder, K.
Dahlström, J. M.
Miranda, M.
Buth, C.
Schafer, K. J.
Mauritsson, J.
L'Huillier, A.
Gisselbrecht, M.
Source :: Physical Review Letters 2010
Publication Year :: 2010
Abstract: We study resonant two-color two-photon ionization of Helium via the 1s3p 1P1 state. The first color is the 15th harmonic of a tunable titanium sapphire laser, while the second color is the fundamental laser radiation. Our method uses phase-locked high-order harmonics to determine the {\it 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.<br />Comment: 4 pages, 5 figures, under consideration