All-Optical Control of the Ultrafast Dynamics of a Hybrid Plasmonic System

We demonstrate complete all-optical and phase-stable control of the linear optical polarization and the nonlinear coherent response (third-harmonic generation) of a hybrid nanoplasmonic-photonic system. A few tens of femtoseconds after the excitation, we turn the response on and off at any given point in time and probe its temporal evolution throughout the control process with a three-pulse nonlinear optical technique. After being switched off, the polarization and the nonlinear radiation remain off permanently. All experiments agree well with numerical simulations based on a damped harmonic oscillator model.

Figure 1

Linear extinction spectrum of the nanostructure showing the two polariton modes. The laser spectrum is shown by a gray profile. Inset: Schematic of the nanostructure. Gold wires with a cross section of $100\times 20\mathrm{nm}$ are fabricated by electron beam lithography, spaced by a period of 530 nm atop of a 180 nm thick hafnium dioxide (${\mathrm{HfO}}_2$) slab waveguide on a quartz substrate.

Figure 2

Simulation of the local polariton polarization excited by a first 8 fs laser pulse and controlled by a second delayed pulse. (a) The second pulse interferes destructively with the polarization, and turns it off (destructive case). Therefore, the polarization is well below the free-induction decay (dashed line). (b) The second pulse interferes constructively with the polarization and reexcites it.

Figure 3

(a) Schematic of the control setup. The start pulse excites the polariton polarization, and the control pulse interferes with it after the delay ${\tau }_c$. The pulses are aligned with normal incidence to the sample and the electric field is polarized perpendicular to the wires. (b) In the third-harmonic regime, photons of each pulse (wave vector ${\mathbf{k}}_1$ and ${\mathbf{k}}_2$) generate higher harmonic photons in their forward directions ($3{\mathbf{k}}_1$ and $3{\mathbf{k}}_2$) and mixed photons in the directions $2{\mathbf{k}}_1+{\mathbf{k}}_2$ and $2{\mathbf{k}}_2+{\mathbf{k}}_1$).

Figure 4

(a)–(c) Experimental results of the coherent nonlinear signal in the direction $2{\mathbf{k}}_2+{\mathbf{k}}_1$ as a function of the time delay ${\tau }_p$ between start and probe pulse for three different delays of the control pulse (${\tau }_c\approx 24$, 35, and 48 fs, marked by the arrows). For the blue line (printed dark gray), the control pulse is switched off, and the free-induction decay of the hybrid mode is visible. The red line (printed gray) always indicates the destructive case. The polariton polarization is turned off after the control pulse and stays off. The green lines (printed light gray) show the constructive case. Here, the polariton polarization is reexcited. (d)–(f) Theoretical results for the coherent nonlinear signal corresponding to panels (a)–(c).