2.3: Total internal reflection
- Page ID
- 128448
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When Snell’s law, , has no solution, there is no refraction; instead, there is total internal reflection with . The ray is reflected inside the medium with higher . Examples include optical fibres. For a fibre whose cladding has only slightly higher , only rays nearly parallel to the fibre axis are internally reflected. So all rays have similar pathlengths and similar transit times. This avoids spreading distortion of ultrashort optical pulses.
- Snell’s law: .
- Total internal reflection, where .
- Applications include fibre optics and their cladding.
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Links to related material |
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| Snells law and refraction Refraction at a plane interface. Derivation of Snell's law. Experimental determination of refractive index. Examples. |
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| Newton's prisms Dispersing white light into component colours, then recombinging them. |
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| Mirages and the Green Flash Refraction from air with a thermally induced density gradient. Inferior mirages. 'Floating islands. The green flash. |
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| Dispersion and chromatic aberration The refractive index varies with wavelength, therefore so does the focal length of a simple lens, giving chromatic dispersion in the image. |
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| Total internal reflection No refraction if the angle of incidence exceeds the critical angle. |
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| Optical fibres and cladding Total internal reflection in an optical fiber. Adding cladding reduces pulse broadening. |
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| Chromatic dispersion, rainbows and Alexander's dark band Dispersion on refraction produces rainbows. One internal reflection gives the primary (40°) rainbow, two gives the secondary (50°) bow. |
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| Colour of the sky Scattering varies strongly with wavelength. Scattered light gives the blue of the sky, and the unscattered light gives the red or orange of a sunset. |
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| Mirrors and images Plane mirrors and virtual images. Inverted images. Real images in a concave mirror. Parabolic reflectors. Fermat's principle. Focusing with mirrors. Aberration. The mirror equation. Convex mirrors. Distortion. |
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| Lenses and images Focussing and forming images with lenses. How to draw ray diagrams. Relating object and image distance to focal length (theory and experiment). |
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| Microscopes and magnifiers The magnifier or simple microscope. The compound microscope and ray diagrams. |
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| Reflecting Newtonian telescope Parabolic reflector and the Newtonian or reflecting telescope. |
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| Refracting telescope Refracting telescope: two converging lenses produces a virtual, inverted image. |
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| Acoustic telescope Parabolic reflector for sound. Compare with Newtonian telescope. Wavelength limitations. |
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Geometrical Optics Experiments |
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