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 (U_{p}) of the laser field. Here, we show that with the unique combination of infrared laser sources (exploiting the quadratic scaling of U_{p}) and plasmonic nanoemitters (which enhance rescattering probability by orders of magnitude) ∼10U_{p} rescattered electrons can be observed in the multiphoton-induced regime. Our experiments correspond well to a model based on the time dependent Schrödinger equation and allowed us to reveal an unexpected aspect of ultrafast electron dynamics in the multiphoton emission regime.