Total internal reflection

Total internal reflection occurs when a wave traveling in a higher-index medium reaches a lower-index boundary above the critical angle and reflects completely back into the first medium.

Snell's law: Snell's law relates the angles of incidence and refraction to the refractive indices of two media. It predicts the refracted angle and yields the critical angle when refraction reaches 90 degrees.
Optical fiber: An optical fiber is a flexible transparent waveguide that carries light through a core surrounded by lower-index cladding. Repeated total internal reflection confines light to the fiber core.
Refraction: Refraction is the change in a wave's direction and speed as it enters a medium where its propagation speed differs. Total internal reflection is the boundary behavior that replaces refraction beyond a limiting incidence angle.
Partial reflection: Partial reflection occurs when an interface sends some incident wave energy back while transmitting the rest. Below the critical angle, an ordinary transmitted wave carries energy into the second medium.
Critical angle: The critical angle is the incidence angle at which a transmitted ray travels along the boundary between two media. Beyond this threshold, no propagating refracted ray enters the lower-index medium.
Fiber-optic communication: Fiber-optic communication transmits information as light pulses through optical fibers. Total internal reflection enables low-loss guidance over long distances.
Refractive index: Refractive index measures how slowly light propagates in a material compared with vacuum. The effect requires light to approach the boundary from the higher-index material.
Brewster's angle: Brewster's angle is the incidence angle at which p-polarized light has zero reflected amplitude at a dielectric interface. It marks polarization-dependent reflection suppression, unlike total reflection beyond the critical angle.
Fresnel equations: The Fresnel equations give the reflected and transmitted amplitudes of light at an interface. They describe how reflection approaches complete intensity as incidence exceeds the critical angle.
Attenuated total reflectance: Attenuated total reflectance is a spectroscopy method that probes samples using an evanescent field at an internal-reflection interface. The field associated with total internal reflection samples material touching the reflecting surface.

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