Journal Article Observation of ionization enhancement in two-color circularly polarized laser fields

Mancuso, Christopher A.  ,  Dorney, Kevin M.  ,  Hickstein, Daniel D.  ,  Chaloupka, Jan L.  ,  Tong, Xiao-Min  ,  Ellis, Jennifer L.  ,  Kapteyn, Henry C.  ,  Murnane, Margaret M.

96 ( 2 )  , p.023402 , 2017-08 , American Physical Society
When atoms are irradiated by two-color circularly polarized laser fields the resulting strong-field processesare dramatically different than when the same atoms are irradiated by a single-color ultrafast laser. For example,electrons can be driven in complex two-dimensional trajectories before rescattering or circularly polarized highharmonics can be generated, which was once thought impossible. Here, we show that two-color circularlypolarized lasers also enable control over the ionization process itself and make a surprising finding: the ionization rate can be enhanced by up to 700% simply by switching the relative helicity of the two-color circularly polarized laser field. This enhancement is experimentally observed in helium, argon, and krypton over a wide range of intensity ratios of the two-color field.We use a combination of advanced quantum and fully classical calculations to explain this ionization enhancement as resulting in part due to the increased density of excited states available for resonance-enhanced ionization in counter-rotating fields compared with co-rotating fields. In the future, this effect could be used to probe the excited state manifold of complex molecules.

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