Energy loss and evanescent waves in total internal reflection

[tade]

In Total Internal Reflection, the beam can still lose some energy as it reflects off the boundary of the medium it is within.

This isn't covered under the Fresnel equations. The energy loss is probably lost in the form of evanescent waves.

I tried searching for the formulae describing the intensities of evanescent waves, but those intensities given seem to be of a transmittance greater than 1, which is impossible.

Anyone know of the correct formula that describes the reflectance of a beam during total internal reflection?

 

[tade]

damn, seems like no one knows the answer to this.

 

[Tom.G]

Look up the definition of "Total"!

For an 'almost' Total, you could also look up the loss in optical fibers.

 

[Drakkith]

I was under the impression that the amount of energy lost is exceedingly close to zero, but I admit I don't know the answer.

 

[Ibix]

Indeed. My somewhat hazy recollection is that evanescent fields don't transport energy (the time average of their Poynting vector is zero), unless they end up overlapping into a medium that can support a normal electromagnetic wave again. So there isn't much of a mechanism for energy loss.

There was a recent thread about evanescent waves in absorbing media. That might be worth looking up.

Edit: https://www.physicsforums.com/threads/adsorption-of-a-evanescent-waves.943570/