Unlocking Coherent Control of Ultrafast Plasmonic Interaction

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 can generate energetic photons beyond the spectrum of the incident beam, where the shortest pulse duration is traditionally expected to induce the greatest nonlinear emission. Here, these photo-induced extreme ultrafast dynamics are coherently controlled by spectrally shaping a sub-10 fs pulse within the timescale of coherent plasmon excitations. Contrary to the common perception, it is shown 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. A detailed theoretical framework that reveals the optimal pulse shapes for enhanced nonlinear emission regarding the nanostructures' plasmonic-resonances is provided. The demonstrated truly-coherent plasma control paves the way to engineer rapid out-of-equilibrium response in solids state systems and light-harvesting applications.

Automated summary

By shaping the pulse and aligning its phase with the plasmon-resonance, the coherent control of photo-induced ultrafast dynamics in metallic nanostructures can enhance the second-order nonlinear emission. This study highlights the crucial role of coherent electronic nature and provides a theoretical framework for optimizing pulse shapes for enhanced nonlinear emission.