In TIR, the reflected photons create an electric field on the opposite site of the interface. Thus, the energy and the angle of incident light must match to create surface plasmon resonance.
However, as plasmons are confined to the plane of the gold film, for SPR it is only the vector component parallel to the surface that matters.
The relative magnitude of the components changes when the angle or wavelength of the incident light changes. The momentum of the photons and plasmons can be described by a vector function with both magnitude and direction. Resonance occurs when the momentum of incoming light is equal to the momentum of the plasmons (momentum resonance). Plasmons have a characteristic momentum defined by factors that include the nature of the conducting film and the properties of the medium on either side of the film. Like all conversions, the photon to plasmon transformation must conserve both momentum and energy in the process. Therefore, when in a TIR situation the quantum energy of the photons is right, the photons convert to plasmons leaving a 'gap' in the reflected light intensity. In accordance with the quantum theory, a plasmon is the particle name of the electron density wave. Photon and electron behaviour can only be described when they have both wave and particle properties. The incident light photons are absorbed and the energy is transferred to the electrons, which convert into surface plasmons. These are the outer shell and conduction-band electrons.
#TOTAL INTERNAL REFLECTION CALCULATOR OMNI FREE#
When the electrical field energy of the photon is just right, it can interact with the free electron constellations in the gold surface. In addition, gold is chemically inert to solutions and solutes typically used in biochemical contexts (1). In most cases, gold is used because it gives a SPR signal at convenient combinations of reflectance angle and wavelength. Now the prism is coated with a thin film of a noble metal on the reflection site. This is called total internal reflection (TIR).Īlthough no light is coming out of the prism in TIR, the electrical field of the photons extends about a quarter of a wavelength beyond the reflecting surface. At this point, all the incoming light reflects within the circular prism. Changing the incidence angle (Θ) changes the out-coming light until it reaches a critical angle. When a light beam hits a half circular prism, the light is bent towards the plane of interface, when it is passing from a denser medium to a less dense one. Surface Plasmon Resonance (SPR) is a physical process that can occur when plane-polarized light hits a thin metal film under total internal reflection conditions (1).
0 kommentar(er)
