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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)
The refractive index is referred to several times as a tensor. This is incorrect, because the property does not transform by the laws of tensors (although permittivity does). See for example "Modern Crystallography IV" Springer series in solid state science v.37, L. A. Shuvalov (Ed.) --FPD.
Could someone also include a discussion on how the ionosphere is birefringent for HF radio waves?
The description contains a very serious error in equation 3a
(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)
The "formal" definition section is wrong, I think, because it fails to take into account that the divergence constraint on the electric field is changed by the anisotropy: now we have . This means, among other things, that the electromagnetic wave equation has to be written in its full form , which does not simplify to if the electric field is not divergence-free.
The easy way to see the error is that the conclusion is absurd: if simply lies along one of the principal axes of ε, then for most directions of there will be no eigensolutions that satisfy the divergence constraint .
I don't have time to fix it now, but I tagged the article as disputed.
(By the way, the subsection on fibers is goofy too, because it mixes up nonlinearity and birefringence when the two have nothing to do with one another. It's also kind of obscurely written, because the semi-vectorial Schrodinger(-like, it's not quantum mechanics) equation is simply an approximation that can be used in low-contrast waveguides.)
—Steven G. Johnson 20:29, 16 December 2005 (UTC)
Sorry for the error in the definition - and thanks for pointing it out. Using the wave equation properly as you quote, I get , which then satisfies the divergence constraint. I will try to correct it, unless you do first.
Note that this problem is, I think, much easier to describe in terms of the magnetic field, since to use the electric field you must inherently solve a generalized eigenproblem (matrices on both sides) or a non-Hermitian problem if you move both matrices to one side. For the magnetic field, you get an ordinary eigenproblem:
with the constraint , where we have written the magnetic field as:
This is an ordinary 3×3 eigenproblem for , which is Hermitian if we neglect material absorption (i.e. if ε is Hermitian) and thus has three orthogonal solution vectors and corresponding eigen-frequencies ω. One of these solutions is ω=0 but violates the divergence constraint, so it is discarded. The other two solutions have magnetic fields orthogonal to k, and correspond to the propagating transverse waves. The corresponding electric field amplitude is given by:
The electric field amplitude is not in general orthogonal to , nor does it generally lie along one of the principal axes of ε. Nor are the two electric field polarizations orthogonal; rather, they satisfy .
Note also that k is the direction of the phase velocity, but is not generally the direction of the group velocity for anisotropic media, and it is the group velocity that determines the direction in which the refracted beams propagate. Note also that the " effective index" is not in general one of the three eigenvalues of , but rather lies in between the eigenvalues. (I seem to recall that it forms an ellipsoid, or at least an ellipse for each possible orientation of .
My own research involves media more complicated than simple homogeneous dielectrics such as this, so I'm probably forgetting some interesting details here, and there might be simpler analysis tricks. e.g. there seem to be all sorts of graphical methods for analyzing these birefringent systems that I've never looked into. But I think I can still spot erroneous approaches.
Note also that for a particular plane of incidence, the resulting solutions have a phase velocity that lies in the same plane, and I believe there are only two refracted solutions even when ε has three distinct eigenvalues. Hence the errors at trirefringence. (The reason that there are only two refracted solutions is obvious from above: for a particular k, there are only two eigenfrequencies corresponding to the two transverse polarizations. Correspondingly, in a given plane of incidence there are only two solution ellipsoids that can be coupled to.) This comes back to the basic misconception that the refracted rays do not in general lie along the principal axes nor are they polarized in those directions.
—Steven G. Johnson 20:27, 29 December 2005 (UTC)
Third time lucky... I hope! Birefringence is more complicated than I thought. My rewrite follows KD Moller Optics p238ff, and it should be correct although it is still not a complete description of course. —Salman Rogers
However, I should point out that there is one hidden assumption in the algebra as you presented it: you are assuming that the eigenvectors of ε are real and orthogonal. This is in general true only for materials in which absorption loss is negligible (or can be treated as a first-order perturbation) and in the absence of magneto-optic effects, in which case ε is a real symmetric matrix. Does your textbook comment on this? —Steven G. Johnson 23:51, 5 January 2006 (UTC)
Hello. According to : (3a)
the is wrong. I just checked it out and I am sure. Any idea? with regards MSchwarz
Hi, MSchwarz again. Please have a look! (2.Maxwell) and with (1.Maxwell) (and and ) .....and there is no anymore...... furthermore you easily can get to the 'wave-equation' with the "großmann-Identität" (german-word, sorry, I dontknow): and as mentioned : (3.Maxwell: ! and )
which is : You`ll find it in any book. And that was the reason for getting into this. Im sure. Greetings from Hamburg, MSchwarz 05:51, 25 June 2006 (UTC)
I suppose checking birefringence values for water ice. Now it stands: 1.309 1.313 +0.014 which are wrong, because 1.313-1.309=0.004, not 0.014. It looks like the mistake is copied from the source website. I have no idea of proper values, if someone has the sources - please check it.
On 16 December 2005, Steven Johnson wrote:
(By the way, the subsection on fibers is goofy too, because it mixes up nonlinearity and birefringence when the two have nothing to do with one another. It's also kind of obscurely written, because the semi-vectorial Schrodinger(-like, it's not quantum mechanics) equation is simply an approximation that can be used in low-contrast waveguides.)
This is Adrian Keister, and I wrote that section on fiber optics. I'm not quite sure I follow your comments.
1. I realize that nonlinearity and birefringence are not the same thing. In what way does the subsection mix them up? It is true that the coupled nonlinear Schrödinger equation takes birefringence into account and is thus a model for birefringence in a fiber optic cable, among other things. See C. Menyuk, Application of multiple-length-scale methods to the study of optical fiber transmission, Journal of Engineering Mathematics 36: 113-136, 1999, Kluwer Academic Publishers, Netherlands, for the derivation of the coupled nonlinear Schrödinger equations starting from Maxwell's equations, and applying the boundary conditions for a fiber optic cable.
2. The coupled nonlinear Schrödinger equations are called that because in applying the Inverse Scattering Transform, the forward scattering problem uses a Lax Pair and , and the operator is typically the Schrödinger operator. The eigenvalue problem, therefore, is the time-independent Schrödinger equation from quantum mechanics. There is thus quite a close link between the Inverse Scattering Transform and quantum mechanics. These equations are not called the coupled nonlinear Schrödinger-like equations.
3. Naturally, since actual solitons do not exist, only a soliton-effect, no one is saying that the equations model the physical situation perfectly. But saying that the equations model the physical situation perfectly is not the same thing as saying that the equations model the physical situation.
4. I'm not sure why the fact that the coupled nonlinear Schrödinger equation is only an approximation renders the subsection "obscurely written."
I would appreciate any comments you might have in reply.
Regards, Adrian
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)
Also - maybe someone who knows about synovial fluid analysis - for diagnosis of gout or pyrophosphate arthropathy - could add something here? Would be useful - this is probably the only application most medical students will find for birefringence.
Just a thought! (G) —Preceding unsigned comment added by 78.145.153.48 ( talk) 08:53, 30 September 2008 (UTC)
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)
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)
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)
Try http://simple.wikipedia.org/wiki/Birefringence —Preceding unsigned comment added by Furrfu ( talk • contribs) 20:26, 23 April 2010 (UTC)
under "Mathematical description" the sentence:
"...., with a relative permittivity tensor ε, where the refractive index n, is defined by ."
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)
True, there is a weird mix of fonts that puzzled me. But also, isn't there a big assumption at this point ? The usual expression of in the scalar case is . If we make the parallel with , then we see that we assumed (or identity matrix). Also, mix of absolute and relative. I don't know if it's a problem or not. Niriel ( talk) 16:37, 8 August 2012 (UTC)
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)
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)
I saw the edit [2] 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)
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...[ [3]]. The lede section is about the phenomenon and referes to the property 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)
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)
The fringes observed on the airbus windshield is wrongly attributed to birefringence, event if it looks similar to a stressed polymer viewed through a polarizer. They are due to thin film interference caused by a conductive Indium Tin Oxide (ITO) thin film deposited on the window for electrical defrosting/defogging. The fringes are strongly visible because the thin film thickness is highly non-uniform on purpose : as the voltage is applied on two opposite points of the window, a uniform conductive film (uniform sheet resistance) would lead to non-uniform current density, and non-uniform defrosting. Some window parts, especially on the sides and far from the electrical contacts, would dissipate less heat, and defrosting would be significantly less efficient here. The ITO thickness pattern is cleverly designed to provide a rather uniform heat dissipation over the whole window.
I worked for 5 years in thin film R&D for the building & automotive industry, including conductive coatings. Now developing a polarized & thin film raytracer. — Preceding unsigned comment added by 88.164.16.51 ( talk) 18:16, 10 June 2013 (UTC)
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)
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. [1]
Ulflund ( talk) 19:51, 25 August 2014 (UTC)
The comment(s) below were originally left at Talk:Birefringence/Comments, and are posted here for posterity. Following several discussions in past years, these subpages are now deprecated. The comments may be irrelevant or outdated; if so, please feel free to remove this section.
The article on birefringence as it presently stands is almost totally inaccessible to a non physicist. Even with a fairly extensive background in chemistry I simply could not understand it. Since I was looking for an explanation of birefringence that I could pass on to a group of non scientists it was no help at all. ping ( talk) 07:24, 30 June 2008 (UTC) |
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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)
The refractive index is referred to several times as a tensor. This is incorrect, because the property does not transform by the laws of tensors (although permittivity does). See for example "Modern Crystallography IV" Springer series in solid state science v.37, L. A. Shuvalov (Ed.) --FPD.
Could someone also include a discussion on how the ionosphere is birefringent for HF radio waves?
The description contains a very serious error in equation 3a
(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)
The "formal" definition section is wrong, I think, because it fails to take into account that the divergence constraint on the electric field is changed by the anisotropy: now we have . This means, among other things, that the electromagnetic wave equation has to be written in its full form , which does not simplify to if the electric field is not divergence-free.
The easy way to see the error is that the conclusion is absurd: if simply lies along one of the principal axes of ε, then for most directions of there will be no eigensolutions that satisfy the divergence constraint .
I don't have time to fix it now, but I tagged the article as disputed.
(By the way, the subsection on fibers is goofy too, because it mixes up nonlinearity and birefringence when the two have nothing to do with one another. It's also kind of obscurely written, because the semi-vectorial Schrodinger(-like, it's not quantum mechanics) equation is simply an approximation that can be used in low-contrast waveguides.)
—Steven G. Johnson 20:29, 16 December 2005 (UTC)
Sorry for the error in the definition - and thanks for pointing it out. Using the wave equation properly as you quote, I get , which then satisfies the divergence constraint. I will try to correct it, unless you do first.
Note that this problem is, I think, much easier to describe in terms of the magnetic field, since to use the electric field you must inherently solve a generalized eigenproblem (matrices on both sides) or a non-Hermitian problem if you move both matrices to one side. For the magnetic field, you get an ordinary eigenproblem:
with the constraint , where we have written the magnetic field as:
This is an ordinary 3×3 eigenproblem for , which is Hermitian if we neglect material absorption (i.e. if ε is Hermitian) and thus has three orthogonal solution vectors and corresponding eigen-frequencies ω. One of these solutions is ω=0 but violates the divergence constraint, so it is discarded. The other two solutions have magnetic fields orthogonal to k, and correspond to the propagating transverse waves. The corresponding electric field amplitude is given by:
The electric field amplitude is not in general orthogonal to , nor does it generally lie along one of the principal axes of ε. Nor are the two electric field polarizations orthogonal; rather, they satisfy .
Note also that k is the direction of the phase velocity, but is not generally the direction of the group velocity for anisotropic media, and it is the group velocity that determines the direction in which the refracted beams propagate. Note also that the " effective index" is not in general one of the three eigenvalues of , but rather lies in between the eigenvalues. (I seem to recall that it forms an ellipsoid, or at least an ellipse for each possible orientation of .
My own research involves media more complicated than simple homogeneous dielectrics such as this, so I'm probably forgetting some interesting details here, and there might be simpler analysis tricks. e.g. there seem to be all sorts of graphical methods for analyzing these birefringent systems that I've never looked into. But I think I can still spot erroneous approaches.
Note also that for a particular plane of incidence, the resulting solutions have a phase velocity that lies in the same plane, and I believe there are only two refracted solutions even when ε has three distinct eigenvalues. Hence the errors at trirefringence. (The reason that there are only two refracted solutions is obvious from above: for a particular k, there are only two eigenfrequencies corresponding to the two transverse polarizations. Correspondingly, in a given plane of incidence there are only two solution ellipsoids that can be coupled to.) This comes back to the basic misconception that the refracted rays do not in general lie along the principal axes nor are they polarized in those directions.
—Steven G. Johnson 20:27, 29 December 2005 (UTC)
Third time lucky... I hope! Birefringence is more complicated than I thought. My rewrite follows KD Moller Optics p238ff, and it should be correct although it is still not a complete description of course. —Salman Rogers
However, I should point out that there is one hidden assumption in the algebra as you presented it: you are assuming that the eigenvectors of ε are real and orthogonal. This is in general true only for materials in which absorption loss is negligible (or can be treated as a first-order perturbation) and in the absence of magneto-optic effects, in which case ε is a real symmetric matrix. Does your textbook comment on this? —Steven G. Johnson 23:51, 5 January 2006 (UTC)
Hello. According to : (3a)
the is wrong. I just checked it out and I am sure. Any idea? with regards MSchwarz
Hi, MSchwarz again. Please have a look! (2.Maxwell) and with (1.Maxwell) (and and ) .....and there is no anymore...... furthermore you easily can get to the 'wave-equation' with the "großmann-Identität" (german-word, sorry, I dontknow): and as mentioned : (3.Maxwell: ! and )
which is : You`ll find it in any book. And that was the reason for getting into this. Im sure. Greetings from Hamburg, MSchwarz 05:51, 25 June 2006 (UTC)
I suppose checking birefringence values for water ice. Now it stands: 1.309 1.313 +0.014 which are wrong, because 1.313-1.309=0.004, not 0.014. It looks like the mistake is copied from the source website. I have no idea of proper values, if someone has the sources - please check it.
On 16 December 2005, Steven Johnson wrote:
(By the way, the subsection on fibers is goofy too, because it mixes up nonlinearity and birefringence when the two have nothing to do with one another. It's also kind of obscurely written, because the semi-vectorial Schrodinger(-like, it's not quantum mechanics) equation is simply an approximation that can be used in low-contrast waveguides.)
This is Adrian Keister, and I wrote that section on fiber optics. I'm not quite sure I follow your comments.
1. I realize that nonlinearity and birefringence are not the same thing. In what way does the subsection mix them up? It is true that the coupled nonlinear Schrödinger equation takes birefringence into account and is thus a model for birefringence in a fiber optic cable, among other things. See C. Menyuk, Application of multiple-length-scale methods to the study of optical fiber transmission, Journal of Engineering Mathematics 36: 113-136, 1999, Kluwer Academic Publishers, Netherlands, for the derivation of the coupled nonlinear Schrödinger equations starting from Maxwell's equations, and applying the boundary conditions for a fiber optic cable.
2. The coupled nonlinear Schrödinger equations are called that because in applying the Inverse Scattering Transform, the forward scattering problem uses a Lax Pair and , and the operator is typically the Schrödinger operator. The eigenvalue problem, therefore, is the time-independent Schrödinger equation from quantum mechanics. There is thus quite a close link between the Inverse Scattering Transform and quantum mechanics. These equations are not called the coupled nonlinear Schrödinger-like equations.
3. Naturally, since actual solitons do not exist, only a soliton-effect, no one is saying that the equations model the physical situation perfectly. But saying that the equations model the physical situation perfectly is not the same thing as saying that the equations model the physical situation.
4. I'm not sure why the fact that the coupled nonlinear Schrödinger equation is only an approximation renders the subsection "obscurely written."
I would appreciate any comments you might have in reply.
Regards, Adrian
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)
Also - maybe someone who knows about synovial fluid analysis - for diagnosis of gout or pyrophosphate arthropathy - could add something here? Would be useful - this is probably the only application most medical students will find for birefringence.
Just a thought! (G) —Preceding unsigned comment added by 78.145.153.48 ( talk) 08:53, 30 September 2008 (UTC)
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)
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)
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)
Try http://simple.wikipedia.org/wiki/Birefringence —Preceding unsigned comment added by Furrfu ( talk • contribs) 20:26, 23 April 2010 (UTC)
under "Mathematical description" the sentence:
"...., with a relative permittivity tensor ε, where the refractive index n, is defined by ."
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)
True, there is a weird mix of fonts that puzzled me. But also, isn't there a big assumption at this point ? The usual expression of in the scalar case is . If we make the parallel with , then we see that we assumed (or identity matrix). Also, mix of absolute and relative. I don't know if it's a problem or not. Niriel ( talk) 16:37, 8 August 2012 (UTC)
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)
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)
I saw the edit [2] 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)
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...[ [3]]. The lede section is about the phenomenon and referes to the property 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)
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)
The fringes observed on the airbus windshield is wrongly attributed to birefringence, event if it looks similar to a stressed polymer viewed through a polarizer. They are due to thin film interference caused by a conductive Indium Tin Oxide (ITO) thin film deposited on the window for electrical defrosting/defogging. The fringes are strongly visible because the thin film thickness is highly non-uniform on purpose : as the voltage is applied on two opposite points of the window, a uniform conductive film (uniform sheet resistance) would lead to non-uniform current density, and non-uniform defrosting. Some window parts, especially on the sides and far from the electrical contacts, would dissipate less heat, and defrosting would be significantly less efficient here. The ITO thickness pattern is cleverly designed to provide a rather uniform heat dissipation over the whole window.
I worked for 5 years in thin film R&D for the building & automotive industry, including conductive coatings. Now developing a polarized & thin film raytracer. — Preceding unsigned comment added by 88.164.16.51 ( talk) 18:16, 10 June 2013 (UTC)
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)
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. [1]
Ulflund ( talk) 19:51, 25 August 2014 (UTC)
The comment(s) below were originally left at Talk:Birefringence/Comments, and are posted here for posterity. Following several discussions in past years, these subpages are now deprecated. The comments may be irrelevant or outdated; if so, please feel free to remove this section.
The article on birefringence as it presently stands is almost totally inaccessible to a non physicist. Even with a fairly extensive background in chemistry I simply could not understand it. Since I was looking for an explanation of birefringence that I could pass on to a group of non scientists it was no help at all. ping ( talk) 07:24, 30 June 2008 (UTC) |
Last edited at 07:24, 30 June 2008 (UTC). Substituted at 09:43, 29 April 2016 (UTC)
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