Tailoring the Ultrafast Dephasing of Quasiparticles in Metallic Photonic Crystals

The ultrafast dephasing of waveguide-plasmon polaritons in metallic photonic crystal slabs is investigated in the femtosecond regime by second-order nonlinear autocorrelation. We find a drastic modification of the dephasing rates due to interaction between localized particle plasmons and optical waveguide modes and subsequent modification of the photonic density of states. In the strong coupling regime our measurements give clear evidence for the appearance of ultrafast polaritonic beat phenomena. All experimental results agree well with theoretical simulations based on a coupled damped harmonic oscillator model.

Figure 1

(a) Sketch of sample geometry with a 100-nm-thick ${\mathrm{T}\mathrm{a}\mathrm{O}}_2$-slab waveguide, (b) scanning electron microscope picture of the noncentrosymmetric gold nanoparticle array with a period of $a_x=a_y=400\mathrm{n}\mathrm{m}$, and (c) measured extinction [$-\ln (T)$, $T$: transmission] spectra for the particle period $a_x=400$ and 520 nm.

Figure 2

(a) Experimental setup for the interferometric autocorrelation measurement with a stabilized Michelson interferometer. (b) A second-order autocorrelation function with the BBO crystal (top) and the optical spectrum (bottom) of the laser pulse with ${\tau }_p=13\mathrm{f}\mathrm{s}$.

Figure 3

(a) Measured second-order interferometric autocorrelation functions for the laser pulse interacting with the nanoparticle fields for three different grating periods $a_x$ of the nanoparticle arrays, and (b) fitted ACFs with the obtained dephasing time $T_2$ of the polariton branches. The individual ACFs are shifted upwards for clarity in each panel. For comparison, the envelope of the ACF for the laser pulse using the BBO crystal is shown.

Figure 4

(a)–(c) Extinction spectra (solid red line) and corresponding SH spectra (dotted blue line) of the laser pulse measured at the nanoparticle fields. (d)–(f) Calculated SH spectra obtained by Fourier transformation of the fitted ACF. Vertical dotted lines mark the position of maxima in the calculated SH spectrum. In (a) the used laser spectrum is superimposed for clarification.