Talk:Huygens–Fresnel principle
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[edit] Criticism
A bit of a crap description, in my view at least. Put simply, Huygen's Principle is that a wave front can be thought of as infinate amount of point sources that produce spherical disturbances that reinforce to produce the secondary wavefront and so on. Although the author mentions how it is related to diffraction, he/she fails to explain how in any significant depth. I feel that too many people on Wikipedia (as brilliant a resource as it is) try to sound clever by using fancy language which at most times is inappropriate. (posted anonymously, 21:21, 2 June 2005 129.67.48.245)
[edit] Be more specific in your critique
Actually I found this explanation fine, and I find Wikipedia to be a good resource in addition to others.
Although I understand your complaint in general, as this does happen (see next paragraph), you yourself did not add any value at all to the definition, nor go into even a decent level of detail on expanding the problems you had with it. Simplicity is good; but you still have to be artful in getting your point across. You didn't imho.
To add your own perspective is fine, but to blurt a brief complaint that has no depth or richness itself, frankly just makes you appear as actually the very kind of person that exploits what nominal personal knowledge you have on a subject for reasons of poor self-confidence.
Try to add useful criticisms with some depth instead of coming off, shall we say, a bit unpleasant?
mmf 06:30, 8 November 2005 (UTC) mmf
- FWIW, I think the description (as of Jul 2007) is really rather good. ErkDemon 17:23, 27 July 2007 (UTC)
[edit] Query
I recently added a short section on the connection between Huygens Principle and the Greens function method. For classical and modern physics, the Huygens Principle and its connection to the Greens Function method is tremendously important. A good reference is The Mathematical Theory of Huygens' Principle (Paperback) by Bevan B. Baker, E. T. Copson. The section was removed without explanation. I do not want to add it again without discussion. Best, Rb
I didn't actually remove it, I integrated it into the previous section. I agree the connection is really important, and I'm glad you brought it up, I just think the current version reads easier. It seemed strange to have a separate section for 2 or 3 sentences. If you plan on expounding, by all means readd it.--Hyandat 19:57, 20 December 2005 (UTC)
[edit] Link?
Thanks Hyandat, I just hadn't noticed. The article on Huygens himself does not mention the principle. Should a link be added there? Best, Rb
[edit] Apostrophe or Hyphen has got to go
Shouldn't it be Huygens-Fresnel principle? Huygens' Principle makes sense, but when compounded the possessive should be on either both names (awkward, probably Huygens' and Fresnel's principle), or neither (the Huygens-Fresnel principle). If this is actually a "Fresnel principle" that belongs to Huygens, then the hyphen is wrong (Huygens' Fresnel principle). I'm not correcting this because I don't know the correct expression. edgarde 20:42, 5 June 2006 (UTC)
- Nope its Huygens-Fresnel Principle, I spent 2 months studying it at university! Rob.derosa 12:19, 25 June 2006 (UTC)
- Thanks for fixing this. edgarde 06:10, 7 July 2006 (UTC)
[edit] di Groot's comment
[note by Siward de Groot: i do not agree with the claim that "the same is true of light passing the edge of an obstacle", because if light passes a narrow slit in vacuum, it causes diffraction bands, but there is no matter in the slit to act as secondary source of light. Rather, the explanation in this case is that:
if an (infinitely large) metal screen is between a source of light and a white wall, then there will be no light falling on the wall. This is because the electromagnetic force of the light acts on the wall, and it also acts on the metal shield, where it gives rise to a secondary electromagnetic force, that is the exact opposite of the original stimulus, so that on the light side of the screen reflected light is apparent, while on the wall side of the screen primary and secondary forces cancel out, so it is dark there.
The secundary force is due to the combined effect of all atoms of the screen. Now if a slit is made in this screen, all parts of this screen still experience the same primary stimulus, and therefore produce the same secondary response, except for the atoms that previously were where now the slit is. Thus the resulting lightness on the wall equals the secondary emission previously caused by these atoms, multiplied by -1 , for every point in time.
It is for this reason that the amplitude of the light apparent on that wall can be computed as if it were caused by secondary sources of light in the slit.]
Moved by --Hyandat 17:52, 23 July 2006 (UTC)
[edit] Fourier transforms
Enormousdude, this section you're editing has more fundamental problems. First the Psi(r) should not be a function of r, but of the field location where you want the result (call it x or something); the r gets integrated out. Second, the integral assumes the functions add up all in the same direction, omitting the cos(theta) that Joe Goodman shows, here on page 66. Perhaps that's why it's a far-field approximation? It's not because all the points in the aperture are in phase; that works for near-field just as well, I think. How it becomes a Fourier transform is not explained at all; it comes from the x ocations off axis corresponding to gradients in r that through the exponential make the varying-frequency sinusoids. So you need to say something about how the r pattern depends on the field location x to get from far-field approximation to Fourier transform. The r in the denominator has negligible variation in the far field, which is why you end up with just the FT of the aperture shape. Dicklyon 00:30, 21 June 2007 (UTC)
[edit] Direction dependance
As I understand it, the circular wavefronts coming from the infinity of points have different amplitude in different directions. In particular, if they have an amplitude of 1 in the forward direction it will be 0 in the reverse direction and in general have an amplitude of (1 + cosθ) / 2. 155.212.242.34 (talk) 20:49, 7 December 2007 (UTC)
[edit] Reference
I am thinking about putting Max Born's book Principles of Optics: Electromagnetic Theory of Propagation, Interference and Diffraction of Light under a new reference section because the book offers some good explanations about Huygens-Fresnel Principle. Bchen4 15:38, 5 March 2008 (UTC)
- I added a references section. But don't just add the book there; use it to add or support something in the article, and put it in a footnote. Let us know if you need help. Dicklyon (talk) 16:14, 5 March 2008 (UTC)
I have added a reference - it is a rather elderly optics book, but this is not a problem except that it may be hard to come by. I think Born and Wolf would be an excellent source - I do not, however, have a copy to hand and would not want to add the reference without being able to see the words directly in front of me. Epzcaw (talk) 19:15, 29 May 2008 (UTC)
[edit] Merge with diffraction
I beleive that most of what is in this article is either in, or should be in the diffraction article. Epzcaw (talk) 20:35, 29 May 2008 (UTC)
- That may be so. But a separate article on this principle still makes sense, especially since it's so useful in general optical problems, as a way to explain rays, Snell's law, etc., not just diffraction. Dicklyon (talk) 20:58, 29 May 2008 (UTC)
I'm not sure what you mean by 'this principle'. Huygens-Fresnel principle is the the idea that each point on a wavefront is a source of secondary waves, which means that a wave is 'diffracted' rather than travelling a set of rays and does, as you say, explain many of the interesting things about how waves propagate, including a waves travelling through a slit, a circular aperture, a grating, a refracting medium and a lens, a wave interacting with a rough surface and a mirror surface, the changing profile of a laser beam, the structure of a focused laser beam, the otuput of an ultrasonic transducer, the receiving field of a radio wave antenna, etc. etc.
I think there is a lot of misunderstanding about diffraction - it is described by many people as 'the way light is bent when it encounters an obstacle', but diffraction, as defined by teh Huygens-Fresnel, or Fraunhoffer, or any other diffraciton integral, relates not just to this but to general wave propagation.
Perhaps the problem lies in the definition of diffraction. Epzcaw (talk) 23:47, 30 May 2008 (UTC)
- No, there's no problem with diffraction. My point is that the H-F principle also explains the normal straight-line propagation of light, the reflection and refraction of rays, and stuff like that that is not generally considered under "diffraction". Huygens even used it to explain the anomalous refraction of Iceland spar. Dicklyon (talk) 00:07, 31 May 2008 (UTC)
'Stuff that is not normally considered under 'diffraction' is exactly my point. Huygens-Fresnel IS diffraction; the Huyges-Fresnel and diffraction articles have severla items in common, and rightly so, so shouldn't they be one and the same, and should include all the aspects mentioned above, or perhaps link to new pages covering specific aspeccts. Diffraction is nto some magical thing that happens when a wave hits an object, it is an in-built feature of wave propagation.
I will maybe have a go at drafting something on my user page, and you could comment on that. But for a week or twoEpzcaw (talk) 06:59, 31 May 2008 (UTC)
Have changed my mind about merge - have redited 'Diffraction' in such a way that this article does not overlap significantly. —Preceding unsigned comment added by Epzcaw (talk • contribs) 17:10, 3 June 2008 (UTC)
