Prof. Robert P. H. Chang’s group from Northwestern University had made significant achievement on nano-optics and publish their work on Nano Letters.
Active control of light has attracted significant research interest due to its applications in optical switching, telecommunications, and photonic integrated circuits. Current developments to this end include acoustic vibrations of nanostructures that offer high modulation frequency and small footprint. While noble metals have been used extensively due to their enhanced interactions with light at their plasmon resonances, in this work led by Peijun Guo, a graduate student in my group, we report the coherent acoustic vibrations of indium-tin-oxide nanorod arrays (ITO-NRAs), which enables broadband optical modulation of the visible range where ITO behaves as a dielectric and support multiple Fabry-Perot type resonances. A high modulation amplitude was achieved using on-plasmon resonance pumping in the near-infrared, which efficiently launches the acoustic phonon modes. By comparing the frequency signatures of the various vibrational modes of the highly uniform nanostructured arrays with their counterparts obtained from finite-element simulations, we further determine of the elastic constants for single-crystalline ITO, even when their bulk values are currently unavailable. Our demonstration of deducing elasticity from the vibrational frequencies of uniform nanostructures can be generalized for the study of elasticity for other materials.