Talk:Evanescent field

Total internal reflection

not clear from explanation why kz is larger than k when total internal reflection occurs.

It does gloss over that. Basically, if you solve the problem of matching the incident, reflected, and refracted waves at the boundaries, you find they all must have the form

$\mathbf {E} (y=0)=\mathbf {E} _{0}e^{-ik_{z}z}$

But we also know from Snell's law that

$n_{1}\sin \theta _{incident}=n_{2}{\frac {k_{z}}{|\mathbf {k} _{refracted}|}}$

When that $\sin \theta _{incident}$ on the left equals $n_{2}/n_{1}$, $k_{z}=|\mathbf {k} _{refracted}|$. For $n_{1}>n_{2}$, at larger incident angles, $k_{z}$ is bigger than $|\mathbf {k} _{refracted}|.$

Practical Applications

See this spectrum article.

References

Could someone please add references to the electric section? Sorry - I don't know how to tag it as needing references. 137.215.6.53 (talk) 07:40, 18 July 2008 (UTC)

We should delete the reference [5] on "evanescent wave coupling". Since I'm not really active on wikipedia, I would leave this to someone else. However, this paper by Yong et.al. seems to give a reference for a general physical phenomenon, yet it is a relatively new, specialiced and totally unknown paper. I recommend one of the standard textbook, such as:

- Jackson, J.D., 1999. Classical Electrodynamics, 3rd ed. Am. J. Phys. 67, 841.
- Novotny, L., Hecht, B., 2006. Principles of Nano-Optics. Cambridge University Press.
- Meschede, D., 2008. Optik, Licht und Laser. Springer DE.

direction of evanescence

Isn't this page lacking the information (or at least needing to put it more clearly) that the direction of the evanescent electric field is the same of the exponential decaying? I have the impression sometimes that people care much about the fact that the evanescent waves "evanesce" exponentially, but this is by no means its most notable characteristic. The fact that the field is in the same direction of this decay is the one worth noting. -- NIC1138 (talk) 05:18, 13 January 2009 (UTC)

Correct me if I'm wrong. My understanding of evanescent waves is that they are already by nature "directional." It would follow that the exponential decay is also directional. Pointing it out, seems to me to be akin to saying "The sky is blue, but it is not black." The last half of the sentence is unnecessary. Simple logic should lead the reader to infer the decay is in the same direction IMHO. --24.63.66.140 (talk) 16:53, 28 August 2009 (UTC)

Merger proposal

As the separate page on "evanescent wave coupling" is quite short, and concentrates on practical applications, it seems to me that it would be better to merge it into this page. Is anybody opposed to this idea ? (RGForbes (talk) 21:43, 11 March 2009 (UTC)).

A merged article would probably have a more consolidated content.-Thurth (talk) 06:54, 9 April 2009 (UTC)

I copied the comment below by User 60.240.156.100 from Talk:Evanescent wave coupling:

I vote for the suggestion that this page be merged with Evanescent Waves. As a non-expert of quantum physics, I have been dragged through these pages from the original article I selected, Quantum Tunnelling. Now I am following increasingly tedious links - it would be easier and more sensible surely to couple Evanscent Waves with their coupling? - JD (Biochemist not physicist!... trying to read about how protons tunnel in neurones... presumably with a quantum shovel?). —Preceding unsigned comment added by 60.240.156.100 (talk) 11:13, 16 July 2009 (UTC)

Since there is no opposing consensus against this merger, I will (forwith) execute the merge of "Evanescent wave coupling" into "Evanescent wave". ----Steve Quinn (formerly Ti-30X) (talk) 02:45, 6 May 2010 (UTC)

Possible addition/correction

I found this article while preparing an exam in photonics and I think a correction might be necessary. My understanding is that an evanescent wave appears when a wave crosses from a denser to a thinner material, in my case optically denser/thinner. This is one of the prerequisites for total reflection, which is connected to the appearance of evanescent waves. Is this true for any electromagnetic wave? Everything I've read seems to imply so, however I'm rather a layman in the field so I'd like to be sure :)

Longbowman3 (talk) 13:57, 16 April 2009 (UTC)

Exhibit

Can I take it that "with an intensity that exhibits exponential decay with distance" means "of an intensity which diminishes exponentially with distance"? Or is something subtler being implied here, something to do with "exhibit" or "decay"? Unfree (talk) 04:56, 7 March 2010 (UTC)

Phenomena

I find "Evanescent waves are a general property of wave-equations" confusing. Surely, an equation is something a human being can write down in pencil on paper. Surely, evanescent waves must be physical phenomena. Surely, "property" and "general property" must have quite well established meanings in science. Can it be said that evanescent waves are phenomena which can be seen to emerge naturally from the wave equations, are implicit in them, or can be accounted for by them? Unfree (talk) 05:19, 7 March 2010 (UTC)

How about "Evanescent waves are one general form of solution to wave equations"? It's referring to the fact that, depending on coordinate system, spatial functions of the forms exp(-az), exp(-j*az), and Bessel/Neumann/Hankel functions (among others) are all permissible solutions to the general wave equation, not specific to Maxwell's equations. 03:52, 16 March 2010 (UTC) —Preceding unsigned comment added by 66.57.254.204 (talk)

Incident angle

Considering the direction of movement and the surface of the medium, one would naturally expect the incident angle of the photon, phonon, or whatever, to refer to the angle between the two, rather than between the photon and the normal to the surface. So "they strike it at an angle greater than the so-called critical angle" would seem to imply less shallow rather than shallower. A rewording is called for, or at least a clarification. (Also, how is "so-called" called for?) Unfree (talk) 05:31, 7 March 2010 (UTC)

EM

"EM waves", I take it, is an abbreviation for electromagnetic waves? If so, let's insert "(EM)" after the first occurrence of "electromagnetic", or even better, spell it out each time. Unfree (talk) 05:38, 7 March 2010 (UTC)

The "nearfield" region

Just a hunch, but thinking about "in the nearfield region within one-third wavelength" makes me wonder whether this might be two ways of saying the same thing. Is it? If so, let's state so explicitly and eliminate a layer of logical abstraction. Unfree (talk) 05:44, 7 March 2010 (UTC). I feel it would be more precise to use the terms induction field or reactive near field and this would avoid the need for mentioning one-third wavelength.Beamtube (talk) 23:56, 24 January 2011 (UTC)

Quantum mechanics

The way "in quantum mechanics" enters the discussion suggests (considering quantum mechanics to be valid) that all that has gone before is phony. It's as if we weren't discussing the real world, but an erroneous, prehistoric notion of it. I'm sure this is a familiar situation to those who learn Maxwell's equations before Schroedinger's, and being unfamiliar with any of them, I'm out of my league here, but an introductory sentence or two ought to suffice to explain why quantum mechanics is unnecessary at the outset, but ought to crop up later. Unfree (talk) 06:08, 7 March 2010 (UTC)

Unit vector notation

Explaining "the unit vector in the z direction" crops up a little late, after we've been exposed to the unit vectors in the x and y directions without any explanation. Also, we're told that alpha is a real number, which, when multiplied by i, gives an imaginary result. That's clear. But it isn't clear at the outset (especially without understanding the unit vector notation) exactly what the "components" are, and what alpha and beta are. Unfree (talk) 06:19, 7 March 2010 (UTC)

Diffraction?

The caption of the pictures of the refracted versus evanescent wave in the "Total internal reflection of light" section incorrectly called the refracted wave the "diffracted wave." I fixed this and also removed a link in that caption to Diffraction limit because I didn't see how it was relevant (admittedly that page does talk about evanescent waves being used to beat the diffraction limit in imaging, but that didn't seem relevant to the picture). If I am wrong in these things, please revert. 165.124.205.144 (talk) 08:13, 27 May 2010 (UTC)

It appears to me that your edit is correct. The caption now reads: Representation of a refracted incident wave and an evanescent wave at an interface. I don't see where diffraction would be invloved in these two images. It seems obvious the wave is "refracting" in the top picture. Thanks for your correction. ----Steve Quinn (formerly Ti-30X) (talk) 18:00, 27 May 2010 (UTC)

History

The history of the discovery should be mentioned. I think two men discovered the wave at about the same time. — Preceding unsigned comment added by 92.27.109.117 (talk) 15:37, 26 February 2013 (UTC)