incident ray lie in the principal section:(负晶体) A There is a angle between optic axis and crystal surface 光轴与晶体表面有一夹角(正入射) 自然光士 optic axis 光輛incident ray lie in the principal section：（负晶体） A）There is a angle between optic axis and crystal surface 光轴与晶体表面有一夹角（正入射 ) 自然光 optic axis 光轴