We introduce and benchmark a robust angularly resolved difference observable $\mathrm{\Delta }$ that isolates continuum electron dynamics in mainbands of RABBITT-like setups. We focus on the regime where the infrared laser intensity is high enough that the freed electron may exchange multiple infrared photons with the probe field, thereby opening higher-order continuum-continuum channels. Full-dimensionality ab initio calculations for hydrogen and helium atoms across a broad range of infrared intensities and photoelectron energies demonstrate that $\mathrm{\Delta }$ reflects the continuum dynamics almost exclusively, with negligible sensitivity to multielectron effects or target-specific details. The close agreement between both targets indicates that the dominant single-electron character of these reactions, previously established for sidebands in the single-photon continuum-continuum regime, persists into mainbands and survives even as higher-order channels become accessible. An analytic model rationalizes these results and provides a direct connection between $\mathrm{\Delta }$ and the infrared laser intensity at the focal spot.

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• Atomic & molecular processes in external fields
• Multiphoton or tunneling ionization & excitation
• Single- and few-photon ionization & excitation
• Ultrafast phenomena