Nanoplasmonic Photoelectron Rescattering in the Multiphoton-Induced Emission Regime

In strong-field laser-matter interactions, energetic electrons can be created by photoemission and a subsequent rescattering and can attain energy as much as 10 times the ponderomotive potential (Uₚ) of the laser field. Here, we show that with the unique combination of infrared laser sources (exploiting the quadratic scaling of Uₚ) and plasmonic nanoemitters (which enhance rescattering probability by orders of magnitude) ~10Uₚ rescattered electrons can be observed in the multiphoton-induced regime. Our experiments correspond well to a model based on the time dependent Schr\"odinger equation and allowed us to reveal an unexpected aspect of ultrafast electron dynamics in the multiphoton emission regime.