Figure 1. The orientations of coordinate frames in the experiment.

The cylindrical axis (Z′) of a crystal (black cylinder) within a cell is oriented in the laser scanning plane (XZ) at an angle, δ, away from the laboratory Z-axis. The laser is directed perpendicularly (into the page) with the linear polarization oriented along E, at an angle, θ, from the Z-axis. The analyzer is oriented along A, at an angle, φ, from the Z-axis.