Fresnel equation

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Fresnel effect

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Fresnel Blender

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In optics and laser technology, Fresnel reflections are often disturbing – particularly when they occur at normal incidence, so that the reflected beam goes back to the source and can have detrimental effects, for example on the operation of a laser. Besides, such reflections can cause unwanted loss of optical power. For such reasons, one often uses measures to suppress Fresnel reflections to some extent. The following measures are common:

Fresnel lens

Complete transmission without any reflection would require impedance matching. Essentially all optical materials (except for some photonic metamaterials) have the relative permeability <$\mu = 1$>, and in that case the impedance depends only on the refractive index. Therefore, the optical reflectivity at such an interface depends only on the refractive indices of the materials, and it vanishes if those indices are identical.

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Fresnel pronunciation

When a light beam (e.g. a laser beam) reaches an interface between two different transparent media, it is partly transmitted into the other medium and partly reflected back into the original medium.

For the simplest case with normal incidence on the interface, the Fresnel reflectivity can be calculated with the following equation:

Fresnel Light

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Quantitatively, the reflectivity and transmissivity at such an interface can be calculated with Fresnel equations for an arbitrary angle of incidence. The reflections themselves are called Fresnel reflections.