24 April 2019
New method to control surface plasmons
Published online 10 March 2016
Researchers find a new method to gain greater control over surface plasmons — particles at metal surfaces used in sensing devices.
When a beam of light hits an opaque object, wavelengths that correspond to allowed energy transitions in the material are absorbed, while others are reflected off its surface.
In a unique set up, shining a second beam at a specific frequency causes a quantum interference effect that results in opening a window of transparency for the first beam to pass through the opaque material — a phenomenon known as electromagnetically induced transparency (EIT).
A side effect of EIT is that the incident light beam disperses outwards so severely that it slows down in its direction of propagation, giving it potential for applications such as storing light quanta carrying digital information for quantum computing.
Metamaterials are materials engineered with physical structures that simulate optical effects, and have been used to give rise to EIT-like effects on incident light beams.
An international team of researchers now show that not only light waves in free space are amenable to this treatment, but a special kind of waves trapped at the surface of metals, known as surface plasmon oscillations can be similarly subjected to EIT-like effects using metamaterials to better control, excite and focus them1.
Surface plasmons are widely used in extremely sensitive sensors and imaging applications. Greater control over their properties would markedly improve the sensitivity and dynamic range of instruments that employ them.
1. Zhang, X. et al. Asymmetric excitation of surface plasmons by dark mode coupling. Sci. Adv. 2, e1501142 (2016).