Talk:Diffraction grating

message: I don't think an LCD can cause a diffraction pattern, and am pretty sure if it could it wouldn't look like that.  Is the picture instead an example of Newton's rings, caused by the close but imperfect separation between the LCD surface and the protective plastic screen?  Atropos235 19:12, 18 February 2007 (UTC)
replies: text: Since it's not clear whether the cell phone picture exhibits grating diffraction or not, I removed it for now.  It looks like a thin-film effect to me. -- Pgabolde
Having seen similar patterns on the LCD of my own cellphone, I found that after cleaning its surface they disappeared. So, in my case, it does seem to be caused at least in part by a thin-film effect, produced by oil (from either my own body or something I handled) left on the surface by my fingers. I infer, partly from the wave-like images in the top part of the pictured LCD, that the thin-film and polarizer effects may both contribute to what we see.71.163.224.207 (talk) 19:25, 7 April 2016 (UTC)

text: I would agree with that explanation, except the pattern and arrangement of the colors doesn't look to me like either. If I was to guess, I'd say we're looking at the reflection of an apple tree from underneath. Oh, and by the way, it is usually frowned upon to alter other people's comments on a talk page, even if it is to correct spelling and grammar. Zaereth (talk) 19:34, 7 April 2016 (UTC)

text: https://isaacmathscience.wordpress.com/iphone-under-the-spotlight/
Isaacto (talk) 10:31, 31 January 2017 (UTC)

text: I never doubted that they could, but nice photos. I simply doubt that's what this photo is showing. The reasoning is that the color scheme is all wrong. For diffraction I'd expect a smooth flow from one color to the next as the viewing angle changes, and by color I mean all the colors of the rainbow. For thin-film interference, I'd expect not the colors of the rainbow, but browns, turquois-greens, deep blues and magentas (not quite rainbow colors, due to the overlapping of certain wavelengths and not others). Thin-film coats invariable have a sort of metallic luster to them. What I would not expect is deep reds and leaf greens and sky blues all jumbled together. Upon further examination, my guess is still a blurry reflection of a plant, like maybe a rose bush. Zaereth (talk) 01:15, 1 February 2017 (UTC)

text: I agree completely, but the best way to do that is in the text. The images should be used carefully, as examples of what the writing is talking about, but they shouldn't be placed about all willy-nilly like a facebook page. They should bear some relevance to thye section where they're placed. The way to fix that problem is to simply write about it (easy part), but that requires going out and finding sources (hard part, in that most of us are just too darn lazy to go get them ourselves). You are most welcome to participate and add something about it. Zaereth (talk) 02:38, 3 February 2017 (UTC)

text: Awesome. Looks great to me. Now that you've planted a seed you can watch it grow. For photos, I personally find it best to just take my own. That avoids any copyright hassle. When I see something that could use a photo I try to create one that will provide a good demonstration. That's not always easy, though, because light and cameras don't always behave like you want them to. (In example, it took over 200 tries to get this photo of a laser's Gaussian profile, and I don't mean 200 photos, but trying everything I could to eliminate the laser speckle as much as possible.) If your photo is fair quality, adequately and honestly explained, there should be no problem uploading it. Just be sure you know what your photographing and don't try to pass it off a something else. In example, I was careful labeling this photo because it is merely simulating the laser in operation. In actual operation the beams wouldn't show up nearly as well. (That alone took about 30 tries, adjusting camera settings, laser intensity, and the fogginess of the room.) If you have further problems, someone on Wikimedia Commons should be able to assist you. Zaereth (talk) 21:56, 3 February 2017 (UTC)
thread_title:  Incorrect Example? 

message: Does anyone feel up to the challenge of writing something easier to understand?  If I didn't already know what to expect I wouldn't understand it. RJFJR 17:16, 14 June 2007 (UTC)
replies: text: Better now? Han-Kwang 18:30, 14 June 2007 (UTC)
replies: text: Much better.  Thank you. RJFJR 22:23, 14 June 2007 (UTC)
thread_title:  Intro sentence too hard 

message: It is my understanding that it isthe thin film effect that causes interference patterns in reflected light from the dataside of cd's and dvd's and that the example on teh page needs to be removed.Allywilson (talk) 16:40, 18 November 2007 (UTC)
thread_title: Example of the cd/dvd

message: I have re-arranged this article, and added some new bits to make it, I hope, more comprehensible, and to have a more logical structure.
The section on 'gratings as dispersive elements' is still a bit of a mish-mash, and I will do more work on this. I don't know enough about the manufacture of gratings to do anything with this section,  but I suspect it is very sketchy and imcomplete Epzcaw (talk) 13:28, 26 May 2008 (UTC)
thread_title:  Editing of the article 

message: I believe that it is important to discuss the concept of diffraction efficiency either within this page or on a page of its own. I think it should be a section within this page. To those who don't know diffraction efficiency is what percent of the incident light is diffracted to a particular diffraction order in reflectance or transmitance (The efficiencies are generally different). Resonant gratings can be designed that for specific conditions (angle, wavelenth, polarization) the diffraction efficiency of a particular order will be 100%. Eranus (talk) 07:44, 24 July 2008 (UTC)
thread_title:  Diffraction efficiency 

message: This is a bit more for the physics students and not the classical way to view diffraction. Since gratings are periodic, one can use the formalism of solid state physics which deals with periodic structures on the atomic scale. Anyway a homegeneous surface can not change the momentum (propagation vector, k) parralel to the surface. This is the relation between translational symmetry and conservation of momentum. A periodic structure conserves only crystal mometnum also known as quasi momentum, it means that the momentum is conserved up to a reciprocal lattice vector K (1/peiod), so if the grating is periodic in the x direction and the structure is homogeneous in the y direction, then
: \vec{k_{out}} = (k_x+mK,k_{y},\sqrt{(n\omega/c)^2-(k_{x}+mK)^2)-k_{y}^2})
where m is the diffraction order and n the refractive index in the region of diffraction (reflection or tansmition). The way form here to the grating formula is very short, all form symmetry point of view. Will be glad to hear opinions if this should be included (Of course better worded)Eranus (talk) 07:44, 24 July 2008 (UTC)
thread_title:  Diffraction from a photonic crystal point of view 

message: The tutorial is divided in the following section:
Section 1: DIFFRACTION GRATINGS ? RULED & HOLOGRAPHIC 
Section 2: MONOCHROMATORS & SPECTROGRAPHS
Section 3: SPECTROMETER THROUGHPUT & ETENDUE
Section 4: OPTICAL SIGNAL?TO?NOISE RATIO AND STRAY LIGHT
Section 5: THE RELATIONSHIP BETWEEN WAVELENGTH AND PIXEL POSITION ON AN ARRAY
Section 6: ENTRANCE OPTICS
It is a tutorial, by J.M. Lerner and A. Thevenon, part of the HORIBA Jobin Yvon company website, on the optics of spectroscopy. It covers: diffraction gratings - ruled and holographic; monochromators and spectrographs; spectrometer throughput and etendue; optical signal-to-noise ratio and stray light; the relationship between wavelength and pixel position of an array; and entrance optics. 
This article will be very helpful on the diffraction grating page as an external link (http://www.jobinyvon.com/SiteResources/Data/Templates/1divisional.asp?DocID=616&v1ID=&lang=) .Afrine (talk) 14:47, 21 November 2008 (UTC)
thread_title: Diffraction Gratings tutorial by J.M. Lerner and A. Thevenon

message: I don't understand what it is that is being depicted in the recently added "density plot" image. The density of what? What does the horizontal axis represent? Is the density of whatever it is represented by the colour value? It does not correspond to anything I see in the main text.  --Lambiam 11:32, 14 August 2014 (UTC)
replies: text: I can't tell either what the picture is supposed to represent. There is nothing on the commons page or the photo caption to tell how the picture was created, what the vertical lines represent, nor anything else about what this has to do with gratings. A quick google search shows no other uses of the term "density plot" so I do not even know what this term means, unless it is the density of the grooves (but those don't look evenly spaced enough to be grooves). Perhaps the author can clarify what the picture is showing. Zaereth (talk) 23:43, 14 August 2014 (UTC)
thread_title:  Density plot 

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thread_title:  External links modified 

message: This article contains the (in my opinion) unrealistic statement "Diffraction colors also appear when one looks at a bright point source through a translucent fine-pitch umbrella-fabric covering". I have never seen diffraction colors through an umbrella, in contrast to when looking through fine silk fabric. An umbrella diffuses the light like frosted glass, whereas silk does not diffuse the light at all. An umbrella is opaque, whereas silk is semi-transparent. Silk and umbrellas contain 4 threads per mm, so the calculated separation between diffraction maxima is 0.13°. If the light is diffused over more than 0.13°, diffraction colors disappear. See the photo of screws seen through silk. The double contours are due to diffraction. In contrast, screws are invisible through an umbrella. Ceinturion (talk) 18:56, 22 May 2021 (UTC)
thread_title:  Umbrella 

message: I remember learning this long ago and have seen it for myself, yet I see no discussion of it on this Wikipedia page and have had no luck tracking down any online discussions of it after multiple Google searches. Why do/can diffraction gratings favor one side over the other, making either their left spectral patterns or their right spectral patterns brighter than the other side? 173.225.198.117 (talk) 21:32, 22 February 2024 (UTC)
replies: text: In a normal grating, the grooves are symmetrical, so they work equally well on left or right. In a blazed grating the grooves are not symmetrical, so they favor one side over the other. Zaereth (talk) 23:52, 22 February 2024 (UTC)
replies: text: The discussion there seems to indicate only one order and one wavelength are so favored: "[M]aximum optical power is concentrated in the desired diffraction order while the residual power in the other orders (particularly the zeroth) is minimized. Since this condition can only exactly be achieved for one wavelength, it is specified for which blaze wavelength the grating is optimized (or blazed)." I don't see how that expands to all lines in all of the orders on one side vs. the other. (Am I missing something?) 192.101.250.94 (talk) 19:47, 27 February 2024 (UTC)
replies: text: Isn't it obvious? Ok, for example, see this tutorial. In a normal grating, you have grooves that are semi-circular in shape separated by flat surfaces. Diffraction occurs due to the same phenomenon responsible for the double-slit experiment. Because the reflective/transmissive surfaces are flat, they work equally well on both sides, but losses occur due to the width of the grooves. In a blazed grating, the cross section is sawtooth shaped, and the flat reflective/transmissive surfaces all angle from the plane of the grating toward one side and not the other. Thus, whether from reflection or refraction, they favor one side over the other. And at just the right angle there really is no width to the grooves, which helps minimize losses. Zaereth (talk) 22:16, 27 February 2024 (UTC)
thread_title:  Brightness differences in left orders vs. right orders