14.17 Double refraction
When a beam of unpolarised light passes through anisotropic crystals such as quartz or calcite, the beam will split up into two refracted beams. This is known as double refraction or birefringence. The direction in which the ray of transmitted light does not suffer double refraction inside the cystal is known as the optic axis. If only one optic axis is present in a crystal then it is called uni-axial crystal. On the other hand if two optic axes are present in a crystal then it is known as biaxial crystals.
Double refraction in calcite crystal is shown in Fig. 14.26. The refracted beams are plane polarised. One beam is polarised along the direction of the optic axis and is known as extraordinary ray (e-ray), while the ...
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