Case of the Degenerated Cone

For the diffraction angle 26 = 90° the diffraction cone degenerates to the plane Pgo passing through the point A2 and perpendicular to the incident ray U = AiA2- The equation of this plane in vector form is  

The plane 90 determines, together with the equation of the receiving slit plane, the line of the intersection of these planes. In the coordinate system CSr the line of the intersection can be obtained easily from Equation (20) by setting the component z of the vector X to 0. Substituting coordinates of vector V and vector U in the coordinate system CS we obtain the equation of a straight line in the receiving slit plane  

An example of the intersection of the degenerated diffraction cone is given in Section 6.6. 

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