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| Explanation of the structure and function of the Wollaston polarizing prism |
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The Wollaston prism consists of two orthogonal calcite prisms which are cemented together on their base. Their optical axes lie perpendicularly to each other and perpendicular to the direction of propagation of the incident light. Light striking the surface of incidence at right angles is refracted in the first prism into an ordinary (o) and an extraordinary (ao) ray. However, these two rays continue to propagate in the same direction.
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axis perpedicular to the plane of projection;
o: ordinary, ao: extraordinary ray. |
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As the optical axis of the second prism is perpendicular to that of the first, the ordinary ray (o) becomes an extraordinary ray (ao) at the boundary surface. Its refractive index changes from n(o) to n(ao); as n(ao) < n(o) the extraordinary ray is refracted away from the axis of incidence. The opposite applies to the original extraordinary ray, now an ordinary ray: overall, therefore, the two partial rays display very different directions.
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