Brewster (unit)

The brewster (B) is a non-SI unit used to measure the susceptibility of a material to photoelasticity, or the value of the stress-optic coefficient of the material. The unit has dimensions reciprocal to those of stress. One brewster is defined to be equal to [math]\displaystyle{ 10^{-12} }[/math] square metres per newton (m²/N or 1/Pa) or [math]\displaystyle{ 10^{-13} }[/math] square centimetres per dyne (cm²/dyn). The unit is named after David Brewster, who discovered stress-induced birefringence in 1816.