Re: Antonym of 'evanescent'?

AES wrote:
In article <47684477$0$31979$426a74cc@xxxxxxxxxxxx>,
<snip>

Evanescent waves (and also antivescent waves) -- e.g., in the cladding region just outside the core of a lossless optical fiber, or in the "evanescent region" just above the interface in the case of lossless total internal reflection -- are fully and totally propagating in character.

They have a k vector (parallel to the interface); they have a Poynting vector and carry power (again, parallel to the surface); and you can get standing waves or interference fringes between two evanescent waves traveling in opposite, or different directions, and so on.

Is this right? I was taught that the evanescent component of the near-field was defined as that component of the electromagnetic field with the wavevector k parallel to surfaces of constant phase. Thus, the evanescent component does not transport energy.

Can two evanescent fields interfere? that's a new one on me, also. Any experiments?

I'm not sure 'antonym' is the right concept: for example, a vector acting on a surface is decomposed into 'normal' and 'tangential' components. Tangential would not be considered the antonym of normal, tho. The total field is decomposed into evanescent and propogating components... given my current understanding of only propogating waves able to transport energy.

Stone's "Radiation and Optics", p 373-375, distinguishes between 'inhomogeneous' and 'homogeneous'. It's not clear if the inhomogeneous wave is purely evanescent or the total field.

You do have to tackle the concept of their being _inhomogeneous_ plane waves, which are (shamefully) neglected in the vast majority of optics texts.

I agree. There's some material in microscopy texts due to the current fad with frustrated internal reflection methods, but the treatment is uniformly shoddy.


More details in <http://www.stanford.edu/~siegman/optics_with_gain.pdf>.


--
Andrew Resnick, Ph.D.
Department of Physiology and Biophysics
Case Western Reserve University
.

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