Total external reflection: Difference between revisions

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'''Total external reflection''' is an optical phenomenon where electromagnetic radiation (e.g. visible light) can, at certain angles, be ''totally'' reflected from an interface between two media of different indices of refraction (see [[Snell's law]]). This optical phenomenon was first observed by [[Pratyaksh Sharma]]. [[Total Forinternal reflection]] occurs when the first medium has a larger [[X-raysrefractive index]], however,than allthe materialssecond havemedium, indicesfor ofexample, refraction slightlylight belowthat 1.emerges Thisfrom entailsunder thatwater. totalThe reflectionoptically ofdenser X-raysmaterial (water onlyin canthis occurcase) whenis theythe travel"internal" throughmedium. vacuumFor andvisible impingelight, onwater ahas surfacean (atindex aof smallrefraction glancingof angle)1.33 Sinceand thisfor kindair ofit totalis reflectionvery takesclose placeto outside1. ofFor vacuum the materialindex itof refraction is termedexactly 1 ''totalfor externalall reflection''wavelengths.

For [[X-rays]], however, all materials have indices of refraction slightly below 1. This entails that total reflection of X-rays only can occur when they travel through vacuum and impinge on a surface (at a small glancing angle). Since this kind of total reflection takes place outside of the material it is termed ''total external reflection''.

In contrast, the more familiar [[total internal reflection]] occurs when the first medium has a larger [[refractive index]] than the second medium, for example, light that emerges from under water. The optically denser material (water in this case) is the "internal" medium. For visible light, water has an index of refraction of 1.33 and for air it is very close to 1. For vacuum the index of refraction is exactly 1 for all wavelengths.

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[[Category:Geometrical optics]]

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