spec

Software for Diffraction

4.4.1.1.3. - Azimuth Fixed (g_mode = 4)

This mode fixes the value of the rotation angle ψ of a reference vector about the scattering vector Q .

Azimuth-fixed mode provides a degree of control that is particularly useful in a surface-diffraction experiment. If the reference vector is chosen to be the surface normal, setting ψ to 90° rotates the surface normal into the plane defined by the scattering vector and the diffractometer θ-2θ axis. This means that the incidence angle α will equal the exit angle β.


The reference vector is defined by the geometry parameters g_haz, g_kaz, and g_laz. Use the macro setaz to specify the (H,K,L) of the reference vector. For example, to set the reference vector to (0,0,2), use

1.FOURC> setaz 0 0 2
2.FOURC>



Azimuth-fixed mode will fail if you try to make measurements with Q parallel to the reference vector, since there is then no way to define a rotation about Q . The remedy is either to switch to another mode (usually the best choice) or to switch to another reference vector.