Rydberg state excitation is an elusive strong-field phenomenon characterized by tunneling of bound electrons without subsequent ionization. Here, investigating theoretically the pulse duration dependence of the modulation of excitation probability versus laser intensity, we unravel the excitation dynamics of electrons driven by an intense laser pulse in the subcycle scale. It is shown that as a consequence of interference between electron wave packets emitted at different times during the capture process, the positions of peaks in the excitation probability of individual excited states critically depend on the types of interference. Specifically, intracycle interference leads to an intensity spacing of approximately $52{\mathrm{TW}/\mathrm{cm}}^2$ for an 800 nm wavelength, which depends on the parity of the excited states, whereas intercycle interference produces a spacing of about $26{\mathrm{TW}/\mathrm{cm}}^2$ and is parity independent. This interference behavior accounts for the strong pulse-duration dependence observed in the modulation of excitation probabilities. Furthermore, we elucidate the physical mechanism underlying the irregular excitation probability patterns that emerge for longer pulse durations. Beyond prior works, our results establish a unified physical picture explaining the distinct multipeak structures observed in both ionization and excitation phenomena, thereby advancing a comprehensive understanding of strong-field electron dynamics.

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• Atomic & molecular processes in external fields
• Multiphoton or tunneling ionization & excitation