Wednesday, 02 November, 2022

Phase-Selective Four-Wave Mixing of Resonant Plasmonic Nanoantennas

V. Giegold, K. Kolataj, T. Liedl, A. Hartschuh

10.1021/acsphotonics.2c01362

Metallic nanoantennas are key components of a wide range of optical techniques that exploit their plasmonic response for signal amplification and extremely sensitive detection. For nonlinear techniques, the higher-order plasmonic response of a nanoantenna can be predicted by the product of the nanoantenna's linear susceptibilities, known as Miller's rule, provided that the spatial field distributions at the fundamental and the nonlinear frequencies are the same. Here, we show that Miller's rule also holds for ultra-broadband excitation pulses and that it can be utilized to predict the frequency dependence of the near-degenerate four-wave mixing (ND-FWM) intensities generated by individual resonant plasmonic nanoantennas. Importantly, this implies that the nanoantenna's nonlinear response can be deterministically controlled and further optimized by varying the spectral phase of the laser pulse. We demonstrate this by measuring the chirp dependence of the ND-FWM signal and observe an enhancement of up to 60% depending on the position of the plasmon resonance with respect to the laser spectrum, in agreement with model predictions. Finally, we exploit this phase control for chirp-selective confocal imaging of resonant nanoantennas. Our findings may help improve the sensitivity of nonlinear techniques such as plasmonenhanced coherent anti-Stokes Raman scattering.