Pulse shaping control of CH3 i multiphoton ionization at 540 nm

A pulse shaping control experiment on multiphoton ionization of the methyl iodide (CH3I) molecule is reported. A range of phase masks were applied in the Fourier plane of a 4f pulse shaper containing a spatial light modulator, causing spectro-temporal modulation in the 540 nm pulses synthesized in an optical parametric amplifier. The ionization process was studied through velocity map imaging of outgoing photoelectrons. Four main ionization channels were identified, with relative yields that are dependent on the pulse shape applied, indicating that the ionization routes can be steered through light manipulation to some extent. The main mechanism for control seems to derive from peak intensity effects, but some features observed in the photoelectron spectra defy this explanation. The role of resonances at the three-photon level is discussed. © 2014 Taylor and Francis.Peer Reviewe