What is the difference between Uniaxial and Biaxial Crystals?

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- GoPhotonics

May 18, 2023

Difference Between Uniaxial and Biaxial Crystals

Uniaxial and biaxial crystals are two types of anisotropic materials that exhibit different optical properties and behaviors due to their crystal structures.


Uniaxial CrystalsBiaxial Crystals
Crystal Structure
Uniaxial crystals have a single optic axis.
Biaxial crystals have two distinct optic axes that intersect at a common point, known as the biaxial point.
Optical Properties
Uniaxial crystals exhibit optical anisotropy only along one direction. This means that uniaxial crystals have a single refractive index perpendicular to the optic axis.
Biaxial crystals exhibit anisotropy along two different directions. This means that biaxial crystals have two different refractive indices in perpendicular directions.
Optical Behavior
When a light ray passes through a uniaxial crystal, it splits into two rays, one of which is ordinary and follows Snell's law, while the other is extraordinary and follows a more complex path.
When a light ray passes through a biaxial crystal, it splits into three rays, one ordinary and two extraordinary. The behavior of these rays is determined by the crystal's optical properties and their orientation relative to the optic axes.
Due to their anisotropic properties, both uniaxial and biaxial crystals exhibit polarization effects when light passes through them. However, biaxial crystals exhibit more complex polarization effects due to the presence of two optic axes.
Uniaxial crystals are often used in polarizers, waveplates, and retardation plates.
Biaxial crystals are utilized in polarizing beam splitters, optical filters, and other optical components.

Uniaxial and Biaxial both belong to the fascinating group of anisotropic materials that possess remarkable properties that set them apart from isotropic substances. They exhibit distinct optical and mechanical characteristics, making them essential components in various scientific and technological applications.