Abstract-Threshold for Terahertz Resonance of Nanoparticles in Water

Dao Xiang, Jian Wu, Joerg Rottler, and Reuven Gordon

Nano Lett., Just Accepted Manuscript

DOI: 10.1021/acs.nanolett.6b00770

Publication Date (Web): May 20, 2016

Copyright © 2016 American Chemical Society

http://pubs.acs.org/doi/abs/10.1021/acs.nanolett.6b00770?journalCode=nalefd

Nanoparticle vibrations are coupled to light through electrostriction, which gives nonlinear optical scattering. We investigated the acoustic response of 2 nm gold nanoparticles using nearly-degenerate four-wave mixing experimental configuration and show that the nonlinear response suddenly turns on at low powers (<100 mW) for continuous-wave (CW) lasers. The observed nonlinear response is a million times larger than typical electronic nonlinearities. The threshold implies a dramatic change in the quality factor of the vibrating nanoparticles, 4 orders of magnitude larger than usual hydrodynamic theory predicts. It is as if the water is removed altogether, which we speculate is the result of the vibrating particle pushing away the water molecules to form a stable cavity. Since these acoustic vibrations extend to terahertz frequencies, there is potential to harness this effect for high speed optical data processing; as well as to probe the dynamics of proteins all having acoustic modes in this range.