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Joker93
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Is there an easy explanation of total internal reflection of light using Quantum mechanics(or QED)?
That's quite an insightful explanation from classical point of view, on the other hand the OP wanted to find a connecting line between total internal reflection and QED description of photons.Roger Dodger said:The term "total internal reflection" is a bit misleading. If I place a light source under the water, its light rays will refract up into the air no matter the light source is placed. All you have to is stand directly over the the light source and you will see it.
Consider a giant arc centered at the point vertically above the light source and at the water/air interface. Think about position a detector along this arc.
With the detector directly overhead, the path of least time (and therefore the path of most constructive interference) is the straight vertical line.
As you rotate the position of the detector along the giant arc, the light has to veer from choosing a straight line directly to the detector to minimize its time in the water. As you rotate the detector increasingly along this arc, this veer has to increase as well, ever-shortening its time in the water.
Finally, when you get to the surface of the water, the path of least time runs along the water, then dives down to the light source at an angle called the critical angle.
Here is another way to think of it:
Fix the light source at a certain depth. Photons will emanate from the light source in all directions. Just ask yourself: In which direction can the light take once it escapes the water to minimize the time needed to reach a detector placed along the arc?
Those light particles that emanate directly upwards will choose to take the path going straight up. However, those hitting the water at an angle will want to veer at an angle such that the path is closer to the water. Why? To stretch the path length differences in the air to make up for the lost time among path lengths in the water. At some point along the water/air surface, the path lengths in water become such that the only way to make up for the path length differences in air is to have the light travel along the surface of the water. The angle at which the photons are striking the surface of the water in this situation is called the critical angle.*
However, running along the surface of the water is the MAXIMUM path length difference in air. Once the angle passes the critical angle, the path length differences in air cannot be made any larger to make up for the lost time and the paths in water begin to destructively interfere.
If this is not clear, I will create diagrams for you.
* Not quite. The critical angle is the one complimentary to this angle, but that's just semantics.
Total internal reflection is a phenomenon that occurs when a ray of light traveling through a medium hits the boundary of a more optically dense medium at an angle greater than the critical angle. This causes the light to be completely reflected back into the original medium instead of being refracted into the second medium.
In quantum mechanics, light is described as a wave and a particle. When a ray of light hits a boundary, it interacts with the atoms and electrons in the material. If the angle of incidence is greater than the critical angle, the wave function of the light cannot penetrate into the second medium and is instead reflected back into the first medium. This can be explained by the quantization of energy levels in the atoms and the wave-particle duality of light.
No, total internal reflection can occur in any material as long as there is a difference in the index of refraction between the two media and the angle of incidence is greater than the critical angle. However, it is most commonly observed in materials with a high index of refraction, such as water, glass, and diamonds.
Total internal reflection has many practical applications, such as in optical fibers used for telecommunication, endoscopes used in medical procedures, and in prisms used in binoculars and cameras. It is also used in reflective coatings for mirrors and anti-reflective coatings for glasses and camera lenses.
One limitation of total internal reflection is that it can only occur when light is passing from a more optically dense medium to a less optically dense medium. If the light is traveling from a less dense medium to a more dense medium, it will be refracted instead of being internally reflected. Additionally, total internal reflection is only possible at angles greater than the critical angle, which varies depending on the materials involved.