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Mapping surface plasmons

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It is well known that a silver fork reflecting light appears grey, or that a gold ring is golden. Stained-glass church windows exhibit various colours, although they are also made up of gold or silver. The colour difference stems from the different morphologies of the metals: continuous films in the first case, nanoparticles in the second. This effect is known since ancient times, and has been theoretically described since a century: when metal particles have dimensions lower than the wavelength of the light illuminating them (typically, a few hundreds of nanometers), the colour of these particles depends on their size and their shape. To illustrate this effect, we can use the analogy of a vibrating piano string. For a given tension on the string, the note produced by the vibrating string depends on its length: the shorter the string is, the more quickly it vibrates and the sharper the sound produced. For nanoparticles under light illumination, a similar effect occurs. If one sends an electromagnetic wave (the light) on a nanoparticle, the latter will be set in "vibration". These vibrations of the electromagnetic field are called "surface plasmons��. Read more »


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