Possible missing rotational degree of freedom within sample rotation matrix

[gustafsonsven]

Hi all,

Are we missing a rotational degree of freedom within the sample rotation matrix?

Currently, the rotation appears to be an intrinsic set of rotations with a rotation about Lab X of chi (R_X_chi) followed by a rotation about the new frame Y (prime) of omega (R_Yp_ome). The rotation matrix, going from sample to lab, is then R = R_X_chi @ R_Yp_ome. Please correct me if I am wrong here.

Should we not have an additional rotation between R_X_chi and R_Yp_O that is a rotation about the Z (R_Zp_phi)? This would make the omega rotation be about that new Y (doube prime, R_Ypp_ome). Specifically, R = R_X_chi @ R_Zp_phi @ R_Ypp_ome. Am I missing something simple that is taking this into account elsewhere in the simulation? Does the addition of this angle prevent the direct solution of the diffraction equations (I have not yet attempted to add the angle and re-derive the equations)?

Thinking just at a sample frame where omega = 0, I believe we need at least two rotations about orthogonal axes to fully define a possible tilt to the rotation axis.

Let me know your thoughts,
Sven