Principle

During the manufacturing process, by subsequent treatment or the
exertion of external forces it is possible to induce tensions in
transparent materials, which bring about optical anisotropy of
those materials. This means that a Iight wave train is split up
into two parts with different oscillation planes when it passes
through these materials. The propagation velocity of the Iight and
hence the diffraction index are dependent on the direction of
travel. This phenomenon is known as stress birefringence or
photoelasticity.

In this experiment the students should realize that when
polarized white Iight passes through optically anisotropic
materials, coloured bright areas appear behind the crossed
analyzer, and these are apparently brought about because the
oscillation planes of parts of the emergent light are
altered.


Benefits


Multifunctional light box - All-in-one: Can be used for geometric optics on the table, colour mixing and on an optical bench

Extension with others sets at anytime, no additional light sources needed, recognition value for students



Tasks


Direct polarized Iight through given photoelastic models,
exerting on these at the same time various pressures which bring
about inner tensions, and analyze the emergent light.

Then investigate whether spectacle lenses display inner
tensions.