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 1 : DOUBLE REFRACTION V.RUPAVATHI BY
 2 : Polarisation The Phenomena of reflection, refraction, interference, diffraction are common to both transverse waves and longitudinal waves. But the transverse nature of light waves is demonstrated only by the phenomenon of polarisation.
 3 : There are a variety of methods of polarizing light. These are the some methods of polarization taking place : Polarization by Transmission Polarization by Reflection Polarization by Refraction Polarization by Scattering
 4 : Reflection Reflection of light is either specular (mirror-like) or diffuse (retaining the energy, but losing the image) depending on the nature of the interface. Furthermore, if the interface is between a dielectric and a conductor, the phase of the reflected wave is retained, otherwise if the interface is between two dielectrics, the phase may be retained or inverted, depending on the indices of refraction. A mirror provides the most common model for specular light reflection, and typically consists of a glass sheet with a metallic coating where the reflection actually occurs. Reflection is enhanced in metals by suppression of wave propagation beyond their skin depths. Reflection also occurs at the surface of transparent media, such as water or glass.
 5 : In the diagram at left, a light ray PO strikes a vertical mirror at point O, and the reflected ray is OQ. By projecting an imaginary line through point O perpendicular to the mirror, known as the normal, we can measure the angle of incidence, ?i and the angle of reflection, ?r. The law of reflection states that ?i = ?r, or in other words, the angle of incidence equals the angle of reflection.
 6 : Example: An Indian triggerfish reflecting in the water surface through total internal reflection
 7 : Refraction is the change in direction of a wave due to a change in its speed. This is most commonly observed when a wave passes from one medium to another. Refraction of light is the most commonly observed phenomenon, but any type of wave can refract when it interacts with a medium, for example when sound waves pass from one medium into another or when water waves move into water of a different depth. Refraction is described by Snell's law, which states that the angle of incidence ?1 is related to the angle of refraction ?2 by Refraction
 8 : where v1 and v2 are the wave velocities in the respective media, and n1 and n2 the refractive indices. In general, the incident wave is partially refracted and partially reflected; the details of this behavior are described by the Fresnel equations. Example: Refraction of light waves in water. The dark rectangle represents the actual position of a pencil sitting in a bowl of water. The light rectangle represents the apparent position of the pencil. Notice that the end (X) looks like it is at (Y), a position that is considerably shallower than (X).
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 11 : Double Refraction Bartholinus discovered that when a ray of unpolarised light is incident on a calcite crystal, two refracted rays are produced. This phenomenon is called double refraction. Hence, two images of a single object are formed. This phenomenon is exhibited by several other crystal like quartz, mica etc.
 12 : When an ink dot on a sheet of paper is viewed through a calcite crystal, two images will be seen in the fig. On rotating the crystal, one image remains stationary, while the other rotates around the first. The stationary image is known as the ordinary image (o), produced by the refracted rays which obey the laws of refraction. These rays are known as ordinary rays. The other image is extraordinary image (e), produced by the refracted rays which do not obey the laws of refraction. These ray are known as extraordinary rays.
 13 : Inside a double refracting crystal produces spherical wave front corresponding to ordinary ray and elliptical wavefront corresponding to extraordinary ray.A point source inside a refracting crystal produces spherical wavefront corresponding to ordinary ray and elliptical wavefront corresponding to extraordinary ray.Inside the crystal there is a particular direction in which both the rays travel with same velocity. The direction is called optic axis. The refractive index is same for both rays and there is no double refraction along this direction
 14 : Birefringence, or double refraction, is the decomposition of a ray of light into two rays (the ordinary ray and the extraordinary ray) when it passes through certain types of material, such as calcite crystals or boron nitride, depending on the polarization of the light. This effect can occur only if the structure of the material is anisotropic (directionally dependent). If the material has a single axis of anisotropy or optical axis, (i.e. it is uniaxial) birefringence can be formalized by assigning two different refractive indices to the material for different polarizations. Birefrigence
 15 : The birefringence magnitude is then defined by : where no and ne are the refractive indices for polarizations perpendicular (ordinary) and parallel (extraordinary) to the axis of anisotropy respectively. The reason for birefringence is the fact that in anisotropic media the electric field vector and the dielectric displacement nonparallel (namely for the extraordinary polarisation), although being linearly related. Birefringence can also arise in magnetic, not dielectric, materials, but substantial variations in magnetic permeability of materials are rare at optical frequencies. Liquid crystal materials as used in Liquid Crystal Displays (LCDs) are also birefringent. can be
 16 : Material   no   ne   ?n   beryl [Be3Al2(SiO3)6] 1.602 1.557 -0.045 calcite [CaCO3 ] 1.658 1.486 0.172 calomel [Hg2Cl2] 1.973 2.656 +0.683 ice [H2O] 1.309 1.313 +0.004 lithium niobate [LiNbO3] 2.272 2.187 -0.085 magnesium fluoride [MgF2 ] 1.380 1.385 +0.006 quartz [SiO2] 1.544 1.553 +0.009 ruby [Al2O3] 1.770 1.762 -0.008 rutile [TiO2] 2.616 2.903 +0.287 peridot [(Mg, Fe)2SiO4] 1.690 1.654 -0.036 sapphire [Al2O3] 1.768 1.760 -0.008 sodium nitrate [NaNO3] 1.587 1.336 -0.251 tourmaline 1.669 1.638 -0.031 zircon, high [ZrSiO4 ] 1.960 2.015 +0.055 zircon, low ZrSiO4 1.920 1.967 +0.047 Examples of uniaxial birefringent materials Uniaxial materials, at 590 nm
 17 : The rhombohedral cleavage block of calcite (calcium carbonate ) produces two images when it is placed over the blue pencil. One of the images is “normal” The other image appears displaced, due to the nature of doublyrefracted light.
 18 : Birefrigence
 19 : Birefringence is widely used in optical devices, such as liquid crystal displays, light modulators, color filters, wave plates, optical axis gratings, etc. It also plays an important role in second harmonic generation and many other nonlinear processes. Applications of Birefringence
 20 : It is also utilized in medical diagnostics: needle aspiration of fluid from a gouty joint will reveal negatively birefringent urate crystals. In ophthalmology, scanning laser polarimetry utilises the birefringence of the retinal nerve fibre layer to indirectly quantify its thickness, which is of use in the assessment and monitoring of glaucoma. Birefringence is also used in optical mineralogy to determine the chemical composition, and history of minerals and rocks.
 21 : Birefringent filters are also used as spatial low-pass filters in electronic cameras, where the thickness of the crystal is controlled to spread the image in one direction, thus increasing the spot-size. This is essential to the proper working of all television and electronic film cameras, to avoid spatial aliasing, the folding back of frequencies higher than can be sustained by the pixel matrix of the camera.
 22 : THANK YOU

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