Abstract
A unique feature of surface plasmon polaritons (SPPs) is that their in-plane momentum is larger than the momentum of free-propagating photons of the same energy. Therefore, it is believed that they can be excited only by evanescent fields created by total internal reflection or by local scattering. Here, we provide the first demonstration of free-space excitation of surface plasmons by means of nonlinear four-wave mixing. The process involves the vectorial addition of the momenta of three incident photons, making it possible to penetrate the light cone and directly couple to the SPP dispersion curve. Using this technique, surface plasmons can be launched on any metal surface by simply overlapping two beams of laser pulses incident from resonant directions. The excitation scheme is also applicable to other bound modes, such as waveguide modes, surface phonon polaritons, and excitations of 2D electron gases.
- Received 25 August 2009
DOI:https://doi.org/10.1103/PhysRevLett.103.266802
©2009 American Physical Society
Synopsis
Never say never to a forbidden transition
Published 19 January 2010
A three-photon process provides a new route toward exciting surface plasmon polaritons on a flat metal surface.
See more in Physics