Frustrated total internal reflection

Frustrated total internal reflection, or FITR, is a phenomenon that occurs when electromagnetic waves reflected within an optical medium(with a lower index of refraction) are interrupted in their internal reflection by an object with a higher refractive index.

In a typical optical system, total internal reflection occurs when a light ray reflects completely inside higher-index medium and reflects onto a lower-index surface.

The optical properties of light can be generally identified through four categories:

• refraction
• reflection
• interference
• diffraction

Refraction occurs when a the speed of a light wave changes as it enters a slower medium. The amount of refraction is determined by the index of refraction between the two different media.