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要旨

We study strong-field ionization of molecular hydrogen in highly intense corotating two-color laser fields. The measured electron momentum distributions show alternating half rings (AHRs) that are characteristic of subcycle interference. We report on the role of the two-color field ratio for the visibility of this subcycle interference. The ratio of the peak electric field at 780 nm compared to the peak electric field at 390 nm E₇₈₀/E₃₉₀ is varied from 0.037 to 0.18. We find very good agreement with the results from our semiclassical simulation. We conclude that the AHR pattern is visible if two conditions are fulfilled. First, the amplitudes of the two pathways that lead to the subcycle interference have to be similar, which is the case for low two-color field ratios E₇₈₀/E₃₉₀. Second, the phase difference of the two pathways must be strong enough to allow for destructive interference, which is the case for high two-color field ratios E₇₈₀/E₃₉₀. For typical experimental conditions, we find that two-color field ratios E₇₈₀/E₃₉₀ in the range from 0.037 to 0.12 lead to good visibility of the AHR pattern. This guides future experiments to measure the Wigner time delay using holographic angular streaking of electrons.