Beam divergence and vertex angle measurements for refractive pyramids

Refractive pyramids are the basic components of the pyramid pupil plane wave-front sensor (WFS). The characteristics of the pyramid are fundamental within the optical design of the WFS and the specifications related to the geometry and optical quality are strongly tight. Here is described a high precision, but rather easy to implement, method for measuring the vertex angle of the refractive pyramids. This angle is calculated from the direct measurements of divergence angle of the refracted beams that represents the most important pyramid characteristic, especially if used in a multi-conjugate adaptive optics application. Moreover an analytical description of the pyramid misalignment effect within the WFS is presented.