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 10 − 12 square metres per newton (m²/N or 1/Pa) or 10 − 13 square centimetres per dyne (cm²/dyn). The unit is named after David Brewster, who discovered stress-induced birefringence in 1816.