Explicit expression for Brewster angles of isotropic-bi-isotropic interface

An explicit expression giving the two Brewster angles for the interface between isotropic and bi-isotropic (nonreciprocal chiral) media is presented. These angles correspond to two eigenpolarisations for which the reflection of a plane wave is zero at the interface. The result contains as a special case an expression for the Brewster angles of the chiral interface, which appears not to have been found earlier in closed form. A qualitatively new effect when compared to the isotropic problem is the appearance of two real Brewster angles for certain bi-isotropic media. This effect is seen to prevail only with nonzero chirality of the medium.