The built-in anisotropy calculation for a single polarization can return skewed values because it samples from a region that may overlap with the beamstop.
Specifically, when calling:
rsoxs.AR(calc2d=False, two_AR=False, chi_width=45, calc2d_norm_energy=None)
the function appears to sample from wedges centered at 0° and -90°. In the data taken in April 2025, the beamstop is located around -50°, so it's very easy for the wedges to include part or all of the beamstop, which can distort the resulting anisotropy calculation.
While I could be mistaken about the exact wedge centers (e.g., if the image is flipped or rotated internally) some basic testing confirmed that the angles near chi=-50° in the unwrapped data do seem to correspond to the beamstop.
Using two polarizations is generally more robust, but single-polarization scans are still sometimes used at the beamline, so it may be more helpful to make this calculation on the basis of the wedges centered at, for example, 90° and 180°.
The built-in anisotropy calculation for a single polarization can return skewed values because it samples from a region that may overlap with the beamstop.
Specifically, when calling:
rsoxs.AR(calc2d=False, two_AR=False, chi_width=45, calc2d_norm_energy=None)the function appears to sample from wedges centered at 0° and -90°. In the data taken in April 2025, the beamstop is located around -50°, so it's very easy for the wedges to include part or all of the beamstop, which can distort the resulting anisotropy calculation.
While I could be mistaken about the exact wedge centers (e.g., if the image is flipped or rotated internally) some basic testing confirmed that the angles near chi=-50° in the unwrapped data do seem to correspond to the beamstop.
Using two polarizations is generally more robust, but single-polarization scans are still sometimes used at the beamline, so it may be more helpful to make this calculation on the basis of the wedges centered at, for example, 90° and 180°.