Total internal reflection
Intermediate
Complete reflection inside a denser medium.
refractionIf the incidence angle exceeds θ_c, all light is reflected back with no loss. It makes diamonds sparkle and optical fibres work.
Binoculars use prisms for TIR.
No energy is transmitted (apart from an evanescent field).
In more detail
Total internal reflection occurs when light travelling in a denser medium strikes the boundary at an angle larger than the critical angle, and all light is reflected back into the denser medium.
Real-world uses
- Prisms in binoculars use total internal reflection to redirect light.
- Optical fibres keep light trapped in the core.
- Diamonds sparkle because light is repeatedly totally internally reflected inside their cut facets.
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Frequently asked questions
Is it a perfect reflection?
Yes, ideally all the light is reflected, unlike ordinary reflection from a mirror.
Why do fibres bend light?
Total internal reflection keeps light inside the bending core.
Does total internal reflection need a particular material?
It needs light to travel from a denser medium toward a less dense one at an angle larger than the critical angle.
Related topics in Optics
Snell's law · Apparent depth · Critical angle · Applications of TIR · Prism and deviation · Dispersion