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Refraction and Reflection

Snell's law of refraction:

The incident ray, the refracted ray and the surface normal are coplanar.

When propagating through a series of parallel interfaces, the quantity nsinθ is conserved.

Law of reflection:

The incident ray, the reflected ray and the surface normal are coplanar.

Reflection equals refraction with n₂ = –n₁.

Total internal reflection TIR occurs when the angle of incidence of a ray propagating from a higher index medium to a lower index medium exceeds the critical angle.

At the critical angle, the angle of refraction θ₂ equals 90°.

The reflectance ρ of an interface between n₁ and n₂ is given by the Fresnel reflection coefficients. At normal incidence with no absorption,