Technical Details
The irradiance of a monochromatic light wave in matter is given in terms of its electric field by
- ,
where E is the complex amplitude of the wave's electric field, n is the refractive index of the medium, is the speed of light in vacuum, and ϵ0 is the vacuum permittivity. (This formula assumes that the magnetic susceptibility is negligible, i.e. where is the magnetic permeability of the light transmitting media. This assumption is typically valid in transparent media in the optical frequency range.)
Irradiance is also the time average of the component of the Poynting vector perpendicular to the surface.
Read more about this topic: Irradiance
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