From 5b5b5a366372bc7f3ac2ef8c11a01b0c4e549fa0 Mon Sep 17 00:00:00 2001 From: watts Date: Thu, 2 May 2024 12:51:09 +0200 Subject: [PATCH] Update SOPHIE Alignment --- SOPHIE-Alignment.md | 22 ++++++++++++++++------ 1 file changed, 16 insertions(+), 6 deletions(-) diff --git a/SOPHIE-Alignment.md b/SOPHIE-Alignment.md index 8bfe03c..b577537 100644 --- a/SOPHIE-Alignment.md +++ b/SOPHIE-Alignment.md @@ -1,21 +1,31 @@ +[[_TOC_]] + +## General Introduction + 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, and the measured change in laser path length being included in the feedback system to erroneously adjust the sample fine stage. +- **Real Drift**: The main drift problem is caused by the ZP stage not moving parallel to X-ray beam axis. +- **Virtual Drift**: A related indirect drift problem is 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. + +Note that a drift will appear worse when looking more closely at it, i.e. the more one zooms in on a sample region, the more sensitive the measurements are to the drift. One should also never expect to completely eliminate drift, but only to minimise it until it is no longer significant. 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. +- **Image Padding Requirements**: 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. +- **Noisy Users**: Complaints during experiments, complaints during analysis, complaints in articles. 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**: 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. +- **Software Correction**: Drifts can be countered by applying a correction in the software of the instrument control system. A software correction can cancel a virtual drift completely by neutralising erroneous feedback systems and therefore eliminating fine stage movement limitations. However, using a software correction to minimise a real drift will increase feedback signals and cause issues with the fine stage limits. + + +## The SOPHIE Endstation + ![SOPHIE_interferometer](uploads/43bfb17f3f46e87154275bf1e8b9672b/SOPHIE_interferometer.png) - - - ![SOPHIE_interferometer](uploads/43bfb17f3f46e87154275bf1e8b9672b/SOPHIE_interferometer.png) \ No newline at end of file +## Fixing the SOPHIE Alignment