Synopsis: Never say never to a forbidden transition

A three-photon process provides a new route toward exciting surface plasmon polaritons on a flat metal surface.
Synopsis figure
Illustration: J. Renger et al., Phys. Rev. Lett. (2009)

Surface plasmon polaritons (SPPs) are electromagnetic waves that are coupled to charge density oscillations at a metal/dielectric interface, and result from light or free electrons hitting the metal surface. The study of SPPs is central to the burgeoning field of plasmonics. From optoelectronics to metamaterials, imaging, and biosensing, SPPs find important applications because they are highly localized at the surface and have well-defined resonant energies.

For a given frequency of light hitting a metal surface from air, the momentum associated with the SPP in the metal will always be greater than the in-plane momentum of the light, so how can one couple to the other? Up to now, the two standard ways of exciting an SPP on a metal with light have been to either use a nonpropagating, or “evanescent,” light wave, or to use a rough or artificially corrugated surface.

Writing in Physical Review Letters, a team of researchers from ICFO in Barcelona, Spain, and the Institute of Optics at the University of Rochester in the US theoretically propose and experimentally demonstrate a new route to SPP excitation from propagating light impinging directly on a flat surface of gold. Their method to produce this “free-space excitation” involves not one but three incident photons at a time, whose momenta add to give the right balance of in-plane momentum for SPP coupling.

These SPPs have well-defined energies, momenta, and directivity. The coupling efficiency is still much too weak for this technique to be practically viable, but the rationale behind this new method could be applied towards exciting other bound modes in related systems, such as surface phonon polaritons, waveguide modes, and excitations in 2D electron gases. – Manolis Antonoyiannakis


Announcements

More Announcements »

Subject Areas

Optics

Previous Synopsis

Next Synopsis

Mesoscopics

The space between

Read More »

Related Articles

Synopsis: Starting Fluid for Laser Fusion
Energy Research

Synopsis: Starting Fluid for Laser Fusion

A laser-based fusion experiment demonstrates that liquid fuel capsules could rectify problems encountered with ice-based fuel capsules. Read More »

Synopsis: Graphene’s Elegant Optics Explained
Graphene

Synopsis: Graphene’s Elegant Optics Explained

Theoretical calculations anchor graphene’s simple optical absorption in its two-dimensional structure instead of its cone-shaped energy bands. Read More »

Synopsis: Sharper Vision for Infrared Telescopes
Optics

Synopsis: Sharper Vision for Infrared Telescopes

Converting infrared light to visible light might boost the sensitivity of infrared telescope arrays. Read More »

More Articles