title: Threshold for Terahertz Resonance of Nanoparticles in Water.
abstract: Nanoparticle vibrations are coupled to light through electrostriction, which gives nonlinear optical scattering. We investigated the acoustic response of 2 nm gold nanoparticles using a 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. Because 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.
authors.affiliation: Department Electrical and Computer Engineering, University of Victoria , Victoria, British Columbia V8P 5C2, Canada.
authors.forename: Dao
authors.initials: D
authors.lastname: Xiang
authors.affiliation: Department Electrical and Computer Engineering, University of Victoria , Victoria, British Columbia V8P 5C2, Canada.
authors.forename: Jian
authors.initials: J
authors.lastname: Wu
authors.affiliation: Department of Physics and Astronomy, University of British Columbia , Vancouver, British Columbia V6T 1Z1, Canada.
authors.forename: Jörg
authors.initials: J
authors.lastname: Rottler
authors.affiliation: Department Electrical and Computer Engineering, University of Victoria , Victoria, British Columbia V8P 5C2, Canada.
authors.forename: Reuven
authors.initials: R
authors.lastname: Gordon
keywords: Four-wave mixing; acoustics; cavitation; electrostriction; nanoparticles; terahertz