Talk:Birefringence

message: I found the text in the current image ("Healthy Eating") to be rather distracting. I took a calcite crystal and took a different photo: http://commons.wikimedia.org/wiki/File:3310.calcite_%28Iceland_Spar%29_birefringence.jpg - would suggest switching to that or something similar. --Furrfu (talk) 17:30, 6 March 2010 (UTC)
thread_title: Image

message: The description contains a very serious error in equation 3a
This is not correct for anisotropic materials as it has used the assumption that the electric field vector E and the electric flux vector D are parallel. In fact, the whole point of anisotropic materials is that these vectors are not parallel to each other. See Born and Wolf. The author appears to have used an isotropic form of Maxwell's Equations in his derivation.
I'm taking the liberty of removing the entire section in question as it is seriously wrong. You should of course, consult a registered expert on this. 193.1.100.105 17:21, 26 October 2007 (UTC)
replies: text: Actually, my bad. Sorry. The epsilon mentioned was a tensor, not a scalar. The section actually seems fine. ObsessiveMathsFreak 00:29, 31 October 2007 (UTC)
thread_title:  (No) Serious Errors in Mathematical Description 

message: Hello. According to :-\nabla \times \nabla \times \mathbf{E}=\frac{1}{c^2}\mathbf{\epsilon} \cdot \frac{\partial^2 \mathbf{E}}{\partial t^2}       (3a)
the \epsilon   is wrong. I just checked it out and I am sure. Any idea? with regards MSchwarz
:Looks right to me (neglecting material dispersion and assuming μ=1).  \nabla \times \mathbf{E} = - \mu \partial\mathbf{H}/\partial ct and \nabla \times \mathbf{H} = \varepsilon \partial\mathbf{E}/\partial ct, so combining these two one gets \nabla \times \frac{1}{\mu} \nabla \times \mathbf{E} = -\frac{\varepsilon}{c^2} \partial^2\mathbf{E}/\partial t^2. —Steven G. Johnson 03:06, 25 June 2006 (UTC)
replies: text: You assumed that \mu \varepsilon = 1/c^2, which is only true in vacuum.  (c always denotes the speed of light in vacuum.)  (If you're confused by the c factors in my explanation, above, it's because I was instinctively using cgs units.  Actually, I tend to set all the dimensionful constants to unity, myself.)   You also assumed that the medium was homogeneous (so that you could pull μ through the derivatives), which I did not, above.  In your final equation, you assumed that the medium was not only homogeneous, but also isotropic, in order to get \nabla\cdot\mathbf{E}=0, which is definitely not the case here.      —Steven G. Johnson 15:31, 27 June 2006 (UTC)
thread_title:  More errors? 

message: Can anyone comment on the role of birefringence in the eye? 
Is the crystalline lens a multifocal lens?
Sapoty 06:50, 7 July 2007 (UTC)
thread_title: Biological subsection

message: One reference is made to negative birefringence, in the context of microscopy.  No other reference is made to birefringence having a polarity.  Please could somebody explain the difference between -ve and +ve birefringence.  —Preceding unsigned comment added by 87.80.19.201 (talk) 14:46, 6 January 2008 (UTC)
thread_title: Negative/positive birefringence

message: Collagen fibres because of their anisotropic properties exhibits berefringency under polarised light. When collagen is stained with picrosirius red, the birefringency becomes even enhanced because picrosirius red posseses anisotropic property too.145.107.12.33 (talk) 13:52, 8 April 2008 (UTC)
thread_title:  Collagen fibres are birefringent 

message: This article as it stands now is almost impossible to understand without a physics background.   I wanted a way to explain birefringence to group of non scientists and got no help at all from the article.
ping (talk) 04:24, 8 June 2009 (UTC)
thread_title:  Uncomprehensible 

message: under "Mathematical description" the sentence:
"...., with a relative permittivity tensor ε, where the refractive index n, is defined by n\cdot n = \epsilon."
is not clear to me. Perhaps a problem with bolds and non-bolds. I also think the comma after "where the refractive index n" shouldn't be there.
160.45.24.185 (talk) 12:16, 20 November 2009 (UTC)
replies: text: The whole section assumes \mu=1 (relative permeability), because μ would otherwise show up in the eigenproblem too.  However, at visible and infrared wavelengths there is almost always negligible magnetic response, so this is usually a valid assumption there. — Steven G. Johnson (talk) 18:38, 8 August 2012 (UTC)
replies: text: Ok!  Then in the Maxwell-Faraday-Ampere equation (\nabla \times \nabla) I'm fine with the \epsilon 1/c^2 with c speed of light in vacuum and \epsilon relative permittivity.  I'm more confused with the \epsilon in Maxwell-Gauss: \nabla \cdot D = \rho with D = \epsilon E but that epsilon is not the relative permittivity, it's \epsilon = \epsilon_r \epsilon_0.  Isn't an \epsilon_0 missing there? Niriel (talk) 08:46, 9 August 2012 (UTC)
thread_title:  Unclear sentence in "Electromagnetic waves in an anisotropic material" 

message: This article does not clarify at all in its table where exactly the x, y and z axes lie with respect to the incident ray and the optical axis in the images. John Riemann Soong (talk) 05:31, 1 November 2010 (UTC)
thread_title:  some help at identifying the axes would be nice 

message: The diagram shows the parallel polarised light refracted more than the perpendicular polarised light, but the caption text says the opposite. Which way is it? -- cheers, Michael C. Price talk 09:07, 25 March 2011 (UTC)
replies: text: If it's this diagram, the caption was indeed stating what you said. It hopefully gives accurate information now, but I'd appreciate a little peer-review just in case. Mikael Häggström (talk) 04:50, 20 May 2011 (UTC)

text: The caption below the diagram also refers to the parallel (s) and perpendicular (p) polarizations which is the incorrect nomenclature. (p) refers to the parallel polarization and (s) to the perpendicular polarization (s being derived from 'senkrecht', the German word for perpendicular) 1.128.97.77 (talk) 04:24, 3 May 2017 (UTC)
replies: text: IP editor, you're right, see Plane of incidence. ('s' and 'p' polarizations are so confusing in English...). It's possible the 'parallel' and 'perpendicular' in the figure are meant to be relative to the optic axis, however this is just adding even more confusion. --Nanite (talk) 15:31, 3 May 2017 (UTC)
thread_title: Diagram wrong?

message: I saw the edit  on positive versus negative birefringence, but reverted it to what was given by the source (ref name=McClatchey509). However, I'm not an expert on the subject myself, so if anyone would give a good reason for these changes, or provide a better reference, then I'd very likely change my mind. Mikael Häggström (talk) 04:42, 20 May 2011 (UTC)
thread_title:  Revert to what was given in source 

message: The first sencente now reads Birefringence, or double refraction, is the decomposition of a ray of light into two rays.... Birefringence is thus refered to as a phenomenon. I think the most common usage of the word is instead as a property of birefringent materials. E.g. Crystals possessing birefringence include...[]. The lede section is about the phenomenon and referes to the property \Delta n=n_e-n_o\, as the birefringence magnitude. The rest of the article on the other hand is all about birefringent materials and the anisotropy of the refractive index, not focusing on the phenomenon of splitting rays. I think the lede should be rewritten to reflect the topic discussed in the rest of the article. I intend to do so when I find time unless someone objects. Ulflund (talk) 17:17, 2 November 2011 (UTC)
replies: text:  I agree that different sections should be allowed to emphasize phenomenon/property differently, but not the lede. The lede should reflect the article. As it is now the lede is about splitting of rays, and the rest of the article about anisotropic refractive index. Ulflund (talk) 17:13, 4 November 2011 (UTC)
replies: text: Looking in the What links here list for birefringence i notice that out of the first 20 pages all except Luminiferous aether referes to birefringence as a material property. [] might be considered notable, and it makes a distinct difference between double refraction (phenomenon) and birefringence (property).  — Preceding unsigned comment added by Ulflund (talk • contribs) 19:01, 6 November 2011 (UTC)
replies: text: All right, sounds good to me. Sho Uemura (talk) 12:29, 8 November 2011 (UTC)
thread_title:  Birefringence as a property or phenomenon 

message: I am a mineralogist, and while I am no expert on optical properties, I was surprised to see peridot listed as a uniaxial substance, but olivine listed as a biaxial one, for two reasons:
Peridot is the gem name for coarsely crystalline, pretty olivine.  They are the identical phase.  Their optical properties should not differ in such a fundamental way.
Every basic textbook on optical mineralogy, including every basic textbook on mineralogy with a chapter on optical (e.g., Klein and Dutrow 2007, Manual of Mineral Science 23rd edition, see p. 300), that I have seen states that uniaxial crystals are in the tetragonal, hexagonal, or trigonal/rhombohedral crystal systems; and biaxial crystals are orthorhombic, monoclinic, and triclinic.  Are there really exceptions to this, and in particular, is there really a gemmy variety of olivine that is one, while most olivine is not?
Def-Mornahan (talk) 16:30, 15 September 2012 (UTC)
replies: text: Removed peridot from uniaxial list. Thanks, Vsmith (talk) 21:40, 15 September 2012 (UTC)
thread_title:  Peridot vs. olivine; uniaxial and biaxial vs. crystal system 

message: The table that gives specific values of the indices of refraction α, β and γ for biaxial materials includes several solid solutions with compositional ranges: biotite K(Mg,Fe)3AlSi3O10(F,OH)2, muscovite KAl2(AlSi3O10)(F,OH)2, olivine (Mg, Fe)2SiO4, and topaz Al2SiO4(F,OH)2. But the indices of refraction of all these materials are composition dependent. Indeed, one way of measuring the composition of, for example, olivine (that is, it's Fe/Mg ratio) is to measure an index of refraction and use the well-known linear relationship between index of refraction and composition in this mineral.
In any case, this means the table values are ill-defined. Olivine (Mg, Fe)2SiO4 can have a value of α anywhere between 1.635 (pure Mg end member) and 1.825 (pure Fe end member), yet here a value is given to four significant digits as if it were a constant applicable to the whole solid solution series. In fact, for olivine the values given all correspond nicely to Mg0.95Fe0.05 composition (source: Deer, Howie and Zussman, An Introduction to the Rock-Forming Minerals, 2nd edition (1992), Longman Scientific and Technical (Essex, England)), which is an unusual but not extremely rare natural composition.
For topaz the three values gives all correspond to a particular specimen with about 19 weight percent F, but natural topaz ranges from ~14 to 20.7 weight percent fluorine.
For biotite and muscovite, the numbers given are within the ranges of natural specimens, but the point remains that these values go with a particular composition along the solid solution series, not with the entire family of compositions. Either that, or these are to be interpreted somehow as average or mid-point values of the range, but if so they should not be given to such high precision (the range, for example, for α for biotite is 1.530-1.625 (variation in 1st decimal place).
Solution: some indication needs to be given that these are example values corresponding to fixed compositions along the indicated solid solutions, or specific values need to be replaced with explicit ranges (this is how they are given in Deer, Howie and Zussman, a fundamental mineralogy reference), or as lower-precision values that can encompass the full range of values within the solid solution.  — Preceding unsigned comment added by Asimow (talk • contribs) 20:57, 4 November 2013 (UTC)
thread_title:  Biaxial materials table -- specific values given for solid solutions are ill-defined 

message: I have removed the following sentence and reference from the birefringence section in the refractive index article since it seemed to specialized. It might fit somewhere in this article though.
In materials simultaneously lacking time-reversal and spatial inversion symmetry (for example multiferroics), refractive indices can be different even for counter-propagating light beams, which effect is termed as directional birefringence.
Ulflund (talk) 19:51, 25 August 2014 (UTC)
thread_title:  Multiferroics 

message: Hello fellow Wikipedians,
I have just modified  on Birefringence. Please take a moment to review my edit. If you have any questions, or need the bot to ignore the links, or the page altogether, please visit this simple FaQ for additional information. I made the following changes:
*Added archive https://web.archive.org/web/20131214030317/http://homepage.ntlworld.com/w.amos2/Brad%20Amos%27s%20Website/BR1.pdf to http://homepage.ntlworld.com/w.amos2/Brad%20Amos%27s%20Website/BR1.pdf
When you have finished reviewing my changes, please set the checked parameter below to true or failed to let others know (documentation at ).
Cheers.—InternetArchiveBot (Report bug) 02:45, 3 November 2016 (UTC)
thread_title:  External links modified 

message: Leaving this image here in case editors of this page find it useful (the subject is far outside my wheelhouse, but I find it interesting, and the image striking). Uploaded by the creator for the Wiki Science Competition (it was one of the finalists in its category). The person who made it has a website explaining how he did it with some other nice images, for anyone interested. — Rhododendrites talk \\ 06:05, 26 January 2018 (UTC)
thread_title:  Image that came through the Wiki Science Competition