The Fresnel Equations describe the behaviour of light beam when moving between two media of differing refractive indices. At the point the beam meets the interface, reflection and/or refraction may occur.
The fraction of the incident light that is reflected from the interface is given by the reflection coefficient R, and the fraction refracted by the transmission coefficient T. The Fresnel equations may be used to calculate R and T in a given situation.
The intensity of the reflected (or transmitted) light is dependant on the polarisation of the incident light. For light with an electric field perpendicular to the plane the above figure (s-polarised), the reflection co-efficient is
R_{s}=( | n_{1} cos(φ_{1})-n_{2}cos(φ) n_{1}cos(φ_{1})+n_{2}cos(φ) | )^{2} |
and for light polarised in the plane of the above figure, the reflection co-efficient is
R_{p}=( | n_{2} cos(φ_{1})-n_{1}cos(φ) n_{2}cos(φ_{1})+n_{1}cos(φ) | )^{2} |
The transmission co-efficients are then found by T_{p}=1-R_{p} and T_{s}=1-R_{s} |