Application of SPPs enables subwavelength optics in microscopy and lithography beyond the diffraction limit. It also enables the first steady-state micro-mechanical measurement of a fundamental property of light itself: the momentum of a photon in a dielectric medium.

In physics, a plasmon is a quantum of plasma oscillation. Just as light (an optical oscillation) consists of photons, the plasma oscillation consists of plasmons. Thus, plasmons are collective (a discrete number) oscillations of the free electron gas density.

As nouns the difference between plasma and plasmon is that plasma is (physics) a state of matter consisting of partially ionized gas while plasmon is (genetics) all the genetic material in an organism.

Surface plasmon resonance (SPR) is the collective oscillation of conduction band electrons that are in resonance with the oscillating electric field of incident light, which will produce energetic plasmonic electrons through non-radiative excitation.

They are a type of surface wave, guided along the interface in much the same way that light can be guided by an optical fiber. SPPs are shorter in wavelength than the incident light (photons). Hence, SPPs can have tighter spatial confinement and higher local field intensity.

SPPs are very sensitive to slight perturbations within the skin depth and because of this, SPPs are often used to probe inhomogeneities of a surface. The electric field (E-field) of an SPP at the silver-air interface, at the frequency where the free-space wavelength is 370 nm. The animation shows how the E-field varies over an optical cycle.

Artificial SPP modes can be realized in microwave and terahertz frequencies by metamaterials; these are known as spoof surface plasmons. The excitation of SPPs is frequently used in an experimental technique known as surface plasmon resonance (SPR).

A new approach that uses plasmon-plasmon interactions has been demonstrated recently. Here the bulk plasmon resonance is induced or suppressed to manipulate the propagation of light.