School of Physics Lecture Demonstration Manual

Oh-4 Dichroism

Published: Wednesday 15 March 2006 - Updated: Monday 28 March 2011

Aim

To demonstrate that the rays produced in an anisotropic body by birefringence have different absorption properties.

Apparatus

Description

The relative absorption of the two orthogonal polarisation states are different for a dichroic crystal. For Tourmaline (a Boron Silicate) the crystal used in this demonstration the ordinary ray will be strongly absorbed, whereas the extraordinary ray will suffer only slight absorption. Hence if light passes through a piece of calcite, the incident beam will be split into two beams polarised vertically to each other. A pinhole stop in front of the calcite will then produce a double image on the projection screen. By means of a dichroic crystal inserted in front of the pinhole stop the two images will appear in different colours.

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