Editing Total internal reflection (section)

== Optical description ==

[[File:Teljes fényvisszaverődés.jpg|thumb|'''Fig.{{nnbsp}}3''':{{big|&nbsp;}}Total internal reflection of light in a semicircular acrylic block]]

Although total internal reflection can occur with any kind of wave that can be said to have oblique incidence, including (e.g.) [[microwave]]s{{r|feynman-1963}} and [[sound]] waves,{{r|antich-et-al-1991}}{{tsp}} it is most familiar in the case of [[light]] waves.

Total internal reflection of light can be demonstrated using a semicircular-cylindrical block of common glass or [[Poly(methyl methacrylate)|acrylic]] glass. In&nbsp;Fig.{{nnbsp}}3, a "ray box" projects a narrow beam of light (a&nbsp;"[[Ray (optics)|ray]]") radially inward. The semicircular cross-section of the glass allows the incoming ray to remain perpendicular to the curved portion of the air/glass surface, and then hence to continue in a straight line towards the flat part of the surface, although its angle with the flat part varies.

Where the ray meets the flat glass-to-air interface, the angle between the ray and the [[normal (geometry)|normal]] (perpendicular) to the interface is called the ''[[angle of incidence (optics)|angle of incidence]]''.<ref>Jenkins & White, 1976, p.{{hsp}}11.</ref> If this angle is sufficiently small, the ray is ''partly'' reflected but mostly transmitted, and the transmitted portion is refracted away from the normal, so that the ''angle of refraction'' (between the refracted ray and the normal to the interface) is greater than the angle of incidence. For the moment, let us call the angle of incidence ''θ''<sub>{{serif|i}}</sub> and the angle of refraction ''θ''<sub>t</sub> (where ''t'' is for ''transmitted'', reserving ''r'' for ''reflected''). As ''θ''<sub>{{serif|i}}</sub> increases and approaches a certain "critical angle", denoted by ''θ''<sub>c</sub> (or sometimes ''θ''<sub>cr</sub>), the angle of refraction approaches 90° (that is, the refracted ray approaches a tangent to the interface), and the refracted ray becomes fainter while the reflected ray becomes brighter.<ref>Jenkins & White, 1976, p.{{hsp}}527. (The refracted beam becomes fainter in terms of total power, but not necessarily in terms of visibility, because the beam also becomes narrower as it becomes more nearly tangential.)</ref> As ''θ''<sub>{{serif|i}}</sub> increases beyond ''θ''<sub>c</sub>, the refracted ray disappears and only the reflected ray remains, so that all of the energy of the incident ray is reflected; this is total internal reflection (TIR). In&nbsp;brief:
* If{{tsp}} ''θ''<sub>{{serif|i}}</sub> &lt; ''θ''<sub>c</sub>{{px2}},{{px2}} the incident ray is split, being ''partly'' reflected and partly refracted;
* If{{tsp}} ''θ''<sub>{{serif|i}}</sub> &gt; ''θ''<sub>c</sub>{{px2}},{{px2}} the incident ray suffers total internal reflection (TIR); none of it is transmitted.