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Total Internal Reflection

What is Total Internal Reflection?

What is Total Internal Reflection?

Total Internal Reflection occurs when light travels from one medium (air,water,glass) into another medium that is less dense. When this happens the angle at which the laser hits the interface of the two mediums is exaggerated.

Say if we take an example of a laser traveling from glass into air. We will start with the laser light traveling straight at the glass and passing through the other side to the interface of where the glass meets the air on the far side –

 

what is total internal reflection 1

what is total internal reflection 1

As we begin to change the angle at which the laser strikes the glass/air interface you will notice the light begins to bend. This is because glass and air have different indexes of refraction. When light changes from a medium with a high index of refraction to a lower index of refraction it is bent back towards itself – the angle gets sharper.

Similarly if it passes from a medium with a lesser index of refraction to a higher index of refraction it is bent way from itself –  the angle gets straightened.

what is total internal reflection 2

what is total internal reflection 2

I will continue increasing the angle at which the laser is striking the glass.air interface –

what is total internal reflection 3

what is total internal reflection 3

what is total internal reflection 4

what is total internal reflection 4

 

Eventually the light will approach an angle called the critical angle. When this angle is exceeded Total Internal Reflection occurs

what is total internal reflection 5

what is total internal reflection 5

Once the critical angle has been found you can continue to trap the laser light by adding more and more glass/air interfaces –

what is total internal reflection 6

what is total internal reflection 6

 

what is total internal reflection 7

what is total internal reflection 7

In fact, this is the principle by which you are probably reading this webpage with. Total Internal Reflection is the principle upon which fiber optic technology works. In the bad old days copper wires were used for internet connections, they are pretty bad at conducting electricity over long distances and can also face electromagnetic interference. Optic fibers can transport more information in a thinner wire and are not affected by electromagnetism.

Optic Fibers and total internal reflection are the reason we have Broadband Internet :).