# Energy Loss During Total Internal Reflection

In summary: It is most readily observed experimentally using microwaves where the blocks can be quite large and easily aligned. With optical wavelengths the experiment is more difficult to do,...
When a laser beam reflects during total internal reflection, how much of its intensity is lost?

I can't the use Fresnel equations as this is for total internal reflection.If you don't know the answer to the above question, what about the same question, but for mirrors instead?

What are the parameters, and more importantly, how does the intensity lost change with the angle of reflection?

When a laser beam reflects during total internal reflection, how much of its intensity is lost?
None. That is what the "total" means

Dale said:
None. That is what the "total" means

but in the real world when you conduct experiments with let's say PMMA, the beam does get weaker with every reflection.

I also mentioned mirrors. Internal reflection within a block could lose energy just a like beam reflecting off a mirror loses energy.

And also this:
...more importantly, how does the intensity lost change with the angle of reflection?

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but in the real world when you conduct experiments with let's say PMMA, the beam does get weaker with every reflection.

The beam gets weaker by absorption and scattering which hapens not only during the reflections..

DrStupid said:
The beam gets weaker by absorption and scattering which hapens not only during the reflections..
true, but from my experience, the reflections do play a major role.

for example, when reflecting in a bar of similar dimensions as shown in the picture above, the increase in path length is not significant enough to produce the attenuation observed, and the beam gets noticeably weaker after each reflection.

true, but from my experience, the reflections do play a major role.

for example, when reflecting in a bar of similar dimensions as shown in the picture above, the increase in path length is not significant enough to produce the attenuation observed, and the beam gets noticeably weaker after each reflection.
Then to my understanding it isn't total internal reflection.

Dale said:
Then to my understanding it isn't total internal reflection.
do you know of any formula that would describe the energy loss for reflection within PMMA or glass etc?

do you know of any formula that would describe the energy loss for reflection within PMMA or glass etc?
I believe what you are looking for is the Fresnel equations

The Fresnel equations that predict total internal reflection will likely never hold perfectly in practice. A good example of where the simple Fresnel formula gets an incomplete/incorrect answer is when you create a case of frustrated total internal reflection by putting a block of the material (usually done with triangular shaped pieces) parallel to and in close proximity of the surface with total internal reflection. As you bring the other block closer and closer, more and more of the beam gets sent through the second block, even though there is an air gap between the two blocks and Fresnel's formulas by themselves would predict total internal reflection. Using the complete Maxwell's equations on this new scenario explains the result completely. In any case, the Fresnel equations that describe total internal reflection, e.g. in a fiber optic cable, are not complete enough to explain reflection losses that will occur.

Dale
A good example of where the simple Fresnel formula gets an incomplete/incorrect answer is when you create a case of frustrated total internal reflection by putting a block of the material (usually done with triangular shaped pieces) parallel to and in close proximity of the surface with total internal reflection. As you bring the other block closer and closer, more and more of the beam gets sent through the second block, even though there is an air gap between the two blocks and Fresnel's formulas by themselves would predict total internal reflection.

that sounds quite bizarre. do you have any links that describe this phenomenon in more detail?

that sounds quite bizarre. do you have any links that describe this phenomenon in more detail?
It is most readily observed experimentally using microwaves where the blocks can be quite large and easily aligned. With optical wavelengths the experiment is more difficult to do, but the same result is found to occur. The Optics book by Klein discusses it. I think if you google "frustrated total internal reflection" you will get a discussion of it. ## \\ ## Editing... A google of it came up with several postings, and one described it as similar to a quantum mechanical type tunneling. When it is so readily performed with microwaves, I don't know whether it is quite at the level of "quantum mechanical tunneling", but in any case if you google it, you should find some interesting discussion of it. A complete explanation is provided using a classical wave description.

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It is most readily observed experimentally using microwaves where the blocks can be quite large and easily aligned. With optical wavelengths the experiment is more difficult to do, but the same result is found to occur. The Optics book by Klein discusses it. I think if you google "frustrated total internal reflection" you will get a discussion of it. ## \\ ## Editing... A google of it came up with several postings, and one described it as similar to a quantum mechanical type tunneling. When it is so readily performed with microwaves, I don't know whether it is quite at the level of "quantum mechanical tunneling", but in any case if you google it, you should find some interesting discussion of it. A complete explanation is provided using a classical wave description.
Unfortunately, I can't apply Frustrated TIR as the scenario I have in mind has only one block of dielectric, not two.

Also, interesting that your posts are consistently 100-150 words long each. how come?

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Dale said:
I believe what you are looking for is the Fresnel equations

I can't the use Fresnel equations as this is for total internal reflection.

If you don't know the answer to the above question, what about the same question, but for silver mirrors instead?

bump in case someone who knows is around

## What is total internal reflection?

Total internal reflection is the phenomenon where a light ray traveling from a denser medium to a less dense medium is completely reflected at the interface between the two mediums, with no portion of the light passing through the interface.

## How does energy loss occur during total internal reflection?

Energy loss during total internal reflection occurs when a portion of the light ray is absorbed by the denser medium at the interface. This absorption of light results in a loss of energy from the original light ray.

## What factors affect the amount of energy loss during total internal reflection?

The amount of energy loss during total internal reflection is affected by the angle of incidence, the refractive indices of the two mediums, and the smoothness of the interface between the two mediums.

## Can energy loss be prevented during total internal reflection?

Energy loss during total internal reflection cannot be completely prevented, but it can be minimized by using materials with lower refractive indices, smoother interfaces, and decreasing the angle of incidence.

## What are the real-world applications of total internal reflection and its energy loss?

Total internal reflection and its energy loss have various applications, such as in fiber optics, where it is used to transmit light signals over long distances through total internal reflection. It is also used in devices like prisms and binoculars to manipulate and redirect light. The energy loss in total internal reflection is also utilized in optical filters and polarizers to reduce unwanted reflections and glare.

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