The race towards fully integrated photonics is on, and plasmons, quantized
plasma density fluctuations in solids, are the vehicle allowing photons to squeeze
into nanoscale device structures. But set aside the huge drive these application
prospects lend to the field - there is a wealth of intriguing and beautiful
physics to explore.
“Plasmonics is rapidly developing into its own discipline at the boundaries
of physics, materials science and chemistry, and leading the way towards a marriage
between photonics and the nanosciences,” Stefan Maier says in the editorial
of the latest issue of 'physica
status solidi - Rapid Research Letters' (pss (RRL)), which is dedicated
to this topic: 'Plasmonics and Nanophotonics'. Maier, acting as the guest editor
of the issue, is convinced that plasmonics is at a very exciting point at the
mo-ment, as our understanding of the electromagnetic properties of nanoscale
systems is applied to more complex systems not only including metals, but also
functional materials that change their properties due to external stimuli. New
materials systems are attracting ever more attention, driven by the need to
overcome the optical losses intrinsic to the most common plasmonic materials,
gold and silver.
Stefan Maier, Co-Director of the Centre for Plasmonics & Metamaterials
at Imperial College London, and his group are researching fundamental light/matter
interactions on the nanoscale as well as applied design of metamaterials, now
aspiring to integrated biological sensors. For his contributions on nanostructured
optical metallic waveguides and on high confinement plasmon waveguiding in the
THz regime, Meier has been honored with the Paterson medal and the Sackler Prize
in Physics in 2010.
The focus issue, which will be freely accessible until January 31th 2011,
comprises 19 invited, yet doubly peer-viewed papers representing a good spectrum
of the variety of plas-monics research currently underway – from a strong
focus on the basic properties of light localization on the nanoscale to hybrid
systems with modulating functionalities and devices.
In the field of integrated surface plasmon (SP) nanophotonics, to communicate
with densely integrated plasmonic components, there is a need for a compact
structure for coupling to SPs, and a corresponding need for a method for determining
the coupling efficiency of any such structures. In the focus issue, a research
group from the University of Central Florida (Orlando, USA) presents their study
of a nanoparticle enhanced grating coupler for exciting SPs on a nearby metal
film. They developed a broadly applicable method to determine the absolute wavelength
dependent coupling efficiency of the miniature coupler, and demonstrate the
presence of both grating-mediated and particle resonance mediated SP excitation.
Another example for a topic the special issues deals with is the excitation
of surface plasmons in nanoapertures, which results in large electromagnetic
field enhancements useful for appli-cations such as surface enhanced Raman scattering
(SERS). The enhancement factor strongly depends on the exact geometrical parameters.
A three-dimensional numerical study carried out by Belgian scientists now indicates
that the excitation of highly confined lateral Fabry–Pérot surface
plasmon resonances results in enhancement factors greatly exceeding the two-dimensional,
long-slit case. Therefore, they anticipate that devices like a special gold
nanoslit-cavity they developed, are particularly interesting for investigating
single molecules.
Regular arrays of metal nanoparticles on metal films have tuneable optical
resonances that can be applied for SERS or biosensing. With the aim of developing
more surface selective geometries, researchers from Graz (Austria) investigated
regular gold nanoparticle arrays on 25 nm thick gold films, which enable excitation
of asymmetric surface plasmon modes featuring a much better field confinement
compared to the symmetric modes used in conventional surface plasmon resonance
setups. They report on the identification of the plasmonic modes sustained by
the structures and reveal the role of modifications in the crystalline structure
of gold on the optical properties.