Fig. 2.

Coordinate system and general interferometer configuration described by the theoretical derivations. The pitch angles of the 3 principal planes relative to the axis of the incident beam are θ, θ₁ and θ₂. The coordinates within the principal planes are (x_n, y_n) and the Y axes of the planes are all perpendicular to the incident beam axis and parallel to each other. The para-axial distances between the source and the 3 principal planes are R_j. In the case of a parallel incident beam the distance R₀ is set to infinity.