Ultrafast electron correlation and ionization pathway competition in hydrogen molecules modulated by counter-rotating two-color circularly polarized laser fields

Using a three-dimensional classical ensemble model (CEM), we investigate ultrafast electron correlation effects in nonsequential double ionization (NSDI) of hydrogen molecules induced by counter-rotating two-color circularly polarized (TCCP) femtosecond laser pulses. Our simulations reveal that the amplitude ratio of the external field dynamically modifies the correlated behavior of the two electrons, making their momentum distribution highly responsive to amplitude fluctuations. Moreover, tuning the amplitude ratio enables precise regulation of the return time of the first ionized electron within the electric field, allowing it to accumulate greater return energy. This energy enhancement subsequently modulates the competitive interplay between recollision-induced ionization (RII) and recollision excitation with subsequent ionization (RESI) pathways.