Fig. 3.

Geometry of the experiment yielding the data shown in Fig. 2. The radiation propagates along the z direction, and the linear polarization vector (magenta) is rotated between the x direction and the y direction (x is in plane on the sample surface) in the magenta-shaded xy plane. The vector c^′ is the projection of the c axis c onto the xy plane. The orientation of the c axis is specified by the angles χ and γ, where χ is the angle between the z direction and c, and γ is the angle between the x direction and c^′.