Total Internal Reflection
Total Internal Reflection is a scenario where a travelling wave of light strikes a boundary of a medium but at an angle that is larger than critical angle. So, the concept behind is that if the refractive index on the other side of the boundary of the medium is lower, and the light wave strikes at greater angle, so the wave is reflected internally entirely. Total internal reflection is a basic concept used in variety of applications for fast travelling of light rays. Total Internal Reflection can also be extended onto various concepts that are arose out of it like frustrated total internal reflection or evanescent waves which are the special cases of this phenomena.
What is Total Internal Reflection?
Consider the following situation. A ray of light passes from a medium of water to that of air. Obviously the light ray will be refracted at the junction separating the two media. Since it passes from a medium of higher refractive index to that having a lower refractive index, the refracted light ray bends away from the normal. At a specific angle of incidence, the incident ray of light is refracted in such a way that it passes along the surface of water.
This particular angle of incidence is called the critical angle. Here the angle of refraction is 90 degrees. So how is the critical angle related to total internal reflection? Any light rays with angles of incidence greater than the critical angle will not cross the water medium at all will they? They will be “reflected” back into the same medium. This is Total Internal Reflection.
Applications of Total Internal Reflection: Diamonds which are used as jewellery are designed and cut in such a way to maximize the amount of light which experience total internal reflection. This makes diamond trap most of the light that enter it, which then undergo several total internal reflections before leaving the diamond, making it supremely shining. Diamond has a very high refractive index.
Optical fibers which are used mainly in telecommunication are another important application of total internal reflection. Optical fibers have revolutionized the speed with which signals are transferred, not only across cities but across countries and continents making telecommunication one of the fastest modes of information transfer. Optical fibers are also used in endoscopy. There are certain rain sensors which control windshield wipers on vehicles that apply the principles of total internal reflection. Certain kinds of touch screens on cameras also use this principle. It is one of the finest breakthrough in the field of communications.