Light, metal and molecules (I)

Surface plasmons can be understood as light trapped on the surface of a metal by interaction with its free electrons. As a result, the electromagnetic field of the plasmon is intense at the metal surface. Surface plasmons have a number of advantages which mean they are used in fields ranging from photonic circuits and components to biomedical sensors for detecting the presence of molecules of interest, or even the detection of single molecules by the exalted Raman signal. Indeed, surface plasmons enable the electromagnetic wave to be concentrated in a sub-wavelength volume, paving the way for the miniaturization of optical components and field exaltation. The properties of surface plasmons can literally be tailor-made by controlling the structure of the metal on a nanometric scale. The dispersion curve (the relationship between frequency and wave vector) of surface plasmons allows us to understand their properties and the consequences of their interactions with molecules.