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
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.
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.