Unlocking coherent control of ultrafast plasmonic interaction

Abstract

Striking a metallic nanostructure with a short and intense pulse of light excites a complex out-of-equilibrium distribution of electrons that rapidly interact and lose their mutual coherent motion. Due to the highly nonlinear dynamics, the photo-excited nanostructures may further emit energetic photons beyond the spectrum of the incident beam, where the shortest pulse duration is traditionally expected to induce the greatest nonlinear emission. Here, we coherently control these photo-induced extreme ultrafast dynamics by spectrally shaping a sub-10 fs pulse within the timescale of coherent plasmon excitations. Contrary to the common perception, we show that stretching the pulse to match its internal phase with the plasmon-resonance increases the second-order nonlinear emission by > 25%. The enhancement is observed only when shaping extreme-ultrashort pulses (< 20 fs), thus signifying the coherent electronic nature as a crucial source of the effect. We provide a detailed theoretical framework that reveals the optimal pulse shapes for enhanced nonlinear emission regarding the nanostructures’ plasmonic-resonances. The demonstrated truly-coherent plasma control paves the way to engineer rapid out-of-equilibrium response in solids state systems and light-harvesting applications.