When a light wave is projected onto a crystal interface, two refracted light beams are generally produced. This phenomenon is called birefringence. Due to the anisotropy of crystal materials, the angle between the two refracted rays is related to the propagation direction and polarization state of the light wave. Crystals that produce birefringence are called birefringent crystals. A birefringent crystal acts like two polarizers with transmission directions perpendicular to each other.
Materials: CaCO3, pure YVO4, quartz crystal, MgF2, and other crystals.