Probing molecular-ion beams with intense few-cycle laser pulses – two-color controlled dissociation

We have studied laser-induced fragmentation of molecular-ion beams using coincidence 3D
momentum imaging, with direct separation of all the reaction products measured simultaneously.
These measurements provide detailed kinetic energy release and angular distributions of the
different fragmentation processes. We mainly focus on the fundamental H2+ and H3+ molecules
(in 5-50 fs laser pulses having 1012-1016 W/cm2 peak intensity) as models for more complex
systems, and at times we explore more complex molecules such as O2+, CO2+ and CO2+.
In this talk, I will describe controlling the nuclear degrees of freedom during dissociation of
molecular-ion beams in a strong-field, which leads to asymmetry in the direction the ionic
fragment is emitted. Specifically, the “control knob” is the relative phase between the 790 and
395 nm components of an ultrashort laser pulse. Of particular interest are phase differences (also
referred to as time delays) between the different dissociating vibrational states.
In addition, clear experimental and theoretical evidence for the intriguing zero-photon
dissociation (ZPD) process of H2+ will be presented. The key role of the laser-pulse bandwidth
and chirp on ZPD control will be discussed. Moreover, we will explore control over the final
dissociation product of HD+, either H+ + D or H + D+ – namely controlling their branching ratio.