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    Birefringence    

 

Birefringence is the effect that a material has different refractive indices for light of different orientations of polarization. An explanation of birefringence can be found here. A material that shows very strong birefringence is calcite, and below are some photos taken of a crystal of calcite.

[ situation I || situation II || situation III ] ⇛ Here you can see the result of rotating the crystal. (2018-01-14)

 

[ no polarizer || polarizer || polarizer rotated 45 degrees || polarizer rotated 90 degrees ] ⇛ These pictures were taken with a polarizer on the camera. The two images that exit the crystal are both polarized because of the birefringence. So when taking a picture through a polarizer with the polarizer at the right angle, it is possible to make one of the two images completely disappear, as can be seen here. (2018-01-14)

 

[ polarizers parallel || polarizers perpendicular ] ⇛ The same principle as the previous photo, but this time with polarized light as the light source, which was done by putting a second polarizer under the crystal. With the polarizers aligned parallel to each other, the light is not blocked in any way. But when having the polarizers perpendicular, all light is blocked. In this case the direction of birefringence of the crystal is either parallel or perpendicular to the direction of polarization of the polarizers. Because of that, the light going through the crystal is blocked as well. This intensifies the iridescence in the crystal (caused by a small crack in the crystal). (2018-01-14)

 

[ polarizers parallel || polarizers perpendicular ] ⇛ The exact same set-up as the previous photo, but with the crystal 45 degrees rotated. In this case, the direction of birefringence in the crystal is 45 degrees to both polarizers, and therefore the light going through the crystal is not blocked. (2018-01-14)

 

A laser beam split in two by a calcite crystal. Each beam represents one of the two directions of polarization. (2018-01-20)

 

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