Entangled photons – Birefringence of light

The birefringence of light has already been known since the 17th century, and was discovered with calcite. Here we show a calcite crystal, lying on a chessboard pattern.

If the light ray hits the crystal, it splits into two polarised parts, that are perpendicular to one another, resulting in a double image.

Using a linear polarisation filter, we can select the two components individually. The horizontal polarised part can be discerned here. Upon rotating the polarisation filter, the slightly offset vertical polarised part becomes visible.