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.

Few-Cycle Surface Plasmon Polaritons.

Surface plasmon polaritons (SPPs) can confine and guide light in nanometer volumes and are ideal tools for achieving electric field enhancement and the construction of nanophotonic circuitry. The realization of the highest field strengths and fastest switching requires confinement also in the temporal domain. Here, we demonstrate a tapered plasmonic waveguide with an optimized grating structure that supports few-cycle surface plasmon polaritons with >70 THz bandwidth while achieving >50% light-field-to-plasmon coupling efficiency.