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Update SOPHIE Alignment

watts
2024-05-02 11:47:44 +02:00
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SOPHIE-Alignment.md

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Microscopes based on Fresnel zone plates will often suffer from "energy drift" where the position of an observed sample feature will vary linearly with respect to the photon energy. This drift is due to systematic positioning errors that occur when the zone plate Z-axis stage moves, and has two parts:
- **Real Drift**: caused by the ZP stage not moving parallel to X-ray beam axis.
- **Virtual Drift**: caused by the interferometer mirror surface not being parallel to the ZP stage movement.
- **Virtual Drift**: caused by the interferometer mirror surface not being parallel to the ZP stage movement, and the measured change in laser path length being included in the feedback system to erroneously adjust the sample fine stage.
There are a number of strategies for dealing with energy drift:
- **Post-fix**: Simply align the images during the data analysis.
- **Rotate Endstation**: This essentially adjusts the X-ray beam axis. One can choose to either minimise the real drift, or to match the virtual drift (with opposite sense) so that they cancel each other out. Note that translating the endstation also results in a small rotation of the X-ray beam axis and so one should take care to reoptimise the endstation position after each rotation. The size and distance of the entrance apertures may limit the amount of endstation rotation that can be applied before the beam is clipped.
- **Adjust Interferometer Mirrors**:
![SOPHIE_interferometer](uploads/43bfb17f3f46e87154275bf1e8b9672b/SOPHIE_interferometer.png)