Giant optomechanical spring effect in plasmonic nano- and picocavities probed by surface-enhanced Raman scattering
Lukas A. Jakob, William M. Deacon, Yuan Zhang, Bart de Nijs, Elena Pavlenko, Shu Hu, Cloudy Carnegie, Tomas Neuman, Ruben Esteban, Javier Aizpurua, Jeremy J. Baumberg
Molecular vibrations couple to visible light only weakly, have small mutual interactions, and hence are often ignored for non-linear optics. Here we show the extreme confinement provided by plasmonic nano- and pico-cavities can sufficiently enhance optomechanical coupling so that intense laser illumination drastically softens the molecular bonds. This optomechanical pumping regime produces strong distortions of the Raman vibrational spectrum related to giant vibrational frequency shifts from an optical spring effect which is hundred-fold larger than in traditional cavities. The theoretical simulations accounting for the multimodal nanocavity response and near-field-induced collective phonon interactions are consistent with the experimentally-observed non-linear behavior exhibited in the Raman spectra of nanoparticle-on-mirror constructs illuminated by ultrafast laser pulses. Further, we show indications that plasmonic picocavities allow us to access the optical spring effect in single molecules with continuous illumination. Driving the collective phonon in the nanocavity paves the way to control reversible bond softening, as well as irreversible chemistry.
Strong nanomechanical Duffing nonlinearity and interactions induced through cavity optomechanics
AMOLF；Australian Research Council Centre of Excellence in Quantum Biotechnology (QUBIC), School of Mathematics and Physics, University of Queensland（昆士兰大学数学与物理学院量子生物技术卓越中心）
