In Fresnel’s equations, the angle of incidence has a strong influence on how much light is transmitted through the boundary between two media. This effect varies based on the refractive indices of the media and the polarization of the light.
- Transmission Decreases at High Incidence Angles:
As the angle of incidence increases (especially approaching grazing angles), the amount of transmitted light generally decreases, and more light is reflected. This is because at steeper angles, the mismatch in wave direction causes more reflection at the interface. - Different Behavior for s- and p-Polarizations:
- For s-polarized light (electric field perpendicular to the plane of incidence), transmission decreases gradually with increasing angle.
- For p-polarized light (electric field parallel to the plane), there is a special angle called the Brewster angle, at which no light is reflected — all of it is transmitted. Beyond this angle, reflection increases again, and transmission falls.
- Total Internal Reflection (TIR):
When light travels from a medium with higher refractive index to one with a lower index, and the incidence angle exceeds the critical angle, transmission drops to zero, and total internal reflection occurs. - Snell’s Law Relation:
Fresnel’s transmission coefficients depend on both the angle of incidence and the angle of refraction, which are linked through Snell’s law. As the incidence angle changes, the angle at which the transmitted wave propagates also changes, affecting transmission intensity.
So, the angle of incidence directly affects both the direction and the amount of transmitted light, making it a crucial factor in optical design.