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Update SOPHIE Alignment

watts
2024-05-02 12:31:29 +02:00
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SOPHIE-Alignment.md

@@ -2,10 +2,15 @@ Microscopes based on Fresnel zone plates will often suffer from "energy drift" w
- **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, and the measured change in laser path length being included in the feedback system to erroneously adjust the sample fine stage.
The consequences of an energy drift include:
- **Misaligned data**: The data stacks must be aligned image-by-image in order to correctly interpret the observations.
- **Extended Image Area**: Image stacks require padding in order to keep features of interest within the measured area over the full energy range.
- **Limited Fine-stage Movement**: A large virtual drift will apply a significant feedback voltage which can push the limits of the sample fine stage and cause a mismatch between the calculate scan-tile regions and the achievable fine stage regions.
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**:
- **Adjust Interferometer Mirrors**: This can be applied to either minimise the virtual drift, or to cancel the real drift. In practice, such adjustments can be very difficult and inconvenient due to the need to vent the system to access the manual adjustment screws and a limited number of adjustment screws included in the implementation of the interferometer system. One must also meet the constraints of having the interferometer beams sufficiently overlap at the detector.