Journal Article Controlling electron-ion rescattering in two-color circularly polarized femtosecond laser fields

Mancuso, Christopher A.  ,  Hickstein, Daniel D.  ,  Dorney, Kevin M.  ,  Ellis, Jennifer L.  ,  Hasović, Elvedin  ,  Knut, Ronny  ,  Grychtol, Patrik  ,  Gentry, Christian  ,  Gopalakrishnan, Maithreyi  ,  Zusin, Dmitriy  ,  Dollar, Franklin J.  ,  Tong, Xiao-Min  ,  Milošević, Dejan B.  ,  Becker, Wilhelm  ,  Kapteyn, Henry C.  ,  Murnane, Margaret M.

93 ( 5 )  , p.053406 , 2016-05 , American Physical Society
High-harmonic generation driven by two-color counter-rotating circularly polarized laser fields was recently demonstrated experimentally as a breakthrough source of bright, coherent, circularly polarized beams in the extreme ultraviolet and soft-x-ray regions. However, the conditions for optimizing the single-atom yield are significantly more complex than for linearly polarized driving lasers and are not fully understood. Here we present a comprehensive study of strong-field ionization—the complementary process to high-harmonic generation—driven by two-color circularly polarized fields. We uncover the conditions that lead to enhanced electron-ion rescattering, which should correspond to the highest single-atom harmonic flux. Using a velocity map imaging photoelectron spectrometer and tomographic reconstruction techniques, we record three-dimensional photoelectron distributions resulting from the strong-field ionization of argon atoms across a broad range of driving laser intensity ratios. In combination with analytical predictions and advanced numerical simulations, we show that “hard” electron-ion rescattering is optimized when the second-harmonic field has an intensity approximately four times higher than that of the fundamental driving field. We also investigate electron-ion rescattering with co-rotating fields, and find that rescattering is significantly suppressed when compared with counter-rotating fields.

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