Double Refraction: How It Works

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In summary, light waves that go near a slit are diffracted more than those that go just through the middle. This phenomenon is called single slit Fraunhofer diffraction.
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Ezio3.1415
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How does double refraction work?
 
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You have presumably looked it (birefringence) up already and you need an explanation of the actual mechanism rather than a simple definition.
It occurs in a medium that is not isotropic - the refractive index along one axis is different from the refractive index along another axis. Refractive index is affected by how the molecules polarise in the presence of an electric field, which, in turn, affects the speed of the wave propagation through the medium. If the medium is a crystal or some 'stressed' amorphous solids, the electrons may be a bit more easily displaced in one direction than in another so the molecules can distort by a different amount. Calcite is the classic example of such a crystal. Light of one plane of linear polarisation travels faster than light in an orthogonal plane and so unpolarised light is split into two beams when it travels through obliquely - the random selection of different polarisation vectors from all the different waves passing through are all resolved into ('H' and 'V') components, corresponding to the two planes in the crystal, each one being refracted by a different amount.
 
  • #3
Thank you for understanding what I meant and answering with a good explanation...

Please tell me if I am right... First there are alternations of E in every direction...When it goes through Calcite the calcite polarizes it... We take two planes perpendicular to each other(principal plane and the other perpendicular to it) and find out the vertical and horizontal component... And as calcite not isotropic regarding the structure of molecules thus the refractive index is not same in the 2 planes... Thus the ray splits into two rays having different velocity and goes different direction...

btw: Why don't we talk about magnetic field alternation when talking about polarization and regarding phenomena?
 
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  • #4
That's quite right enough for starters. We only consider the E field because the fields are at right angles and the H field doesn't need to be described. The ratio may be different for different media though.
 
  • #5
Thank you...

Another question... In single slit fraunhofer diffraction, only the light which goes near the slit is diffracted... If it goes just through the middle it will not be... If the slit is really small would light be diffracted even if it goes through middle?

And do all light waves that go near the slit diffract? Does all light that goes through the middle go undiffracted and contribute to central maximum? What would be the classic and quantum interpretation of this question?
 

1. What is double refraction?

Double refraction, also known as birefringence, is a phenomenon where a single ray of light splits into two rays as it passes through certain materials. This is due to the different speeds at which the light rays travel through the material, resulting in two distinct paths.

2. How does double refraction occur?

Double refraction occurs when light enters a material with an anisotropic crystal structure, meaning that the atoms within the material are arranged in a non-uniform pattern. This causes the light rays to travel at different speeds in different directions, resulting in the splitting of the light ray.

3. What materials exhibit double refraction?

Double refraction can occur in various materials, including crystals such as calcite, quartz, and topaz. It can also occur in some plastics, like cellophane, and certain types of glass. However, not all materials with anisotropic crystal structures exhibit double refraction.

4. How is double refraction useful?

Double refraction has numerous practical applications, such as in polarizing filters for cameras and sunglasses, as well as in optical instruments like polarimeters and polariscopes. It is also used in scientific research to study the internal structures of crystals.

5. Can double refraction be observed in everyday life?

Yes, double refraction can be observed in everyday life. For example, if you place a transparent calcite crystal over a printed paper, you will see a double image due to the double refraction of light passing through the crystal. Some sunglasses also use polarizing filters that take advantage of double refraction to reduce glare.

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