Aligning microscope components

The zone plate and OSA are each mounted on kinematic mounts. If you remove them and replace them, they come back to within a few $\mu$m of the same position. However, when you insert new optics for the first time, you will need to align them.

If you want to remove ZP and OSA, begin by removing the specimen stage using the button in the Edit Alignment menu of the program SM_GUI. You can then remove the OSA, and after that you can remove the ZP. The OSA is held in place with some magnets, while the ZP is locked in place with a $\sim 80$ mm diameter thumbwheel. When taking out the ZP be careful not to bump into the exit snout (it needs the be turned all the way upstream with the micrometer screw first, close the closest beamline valve just in case) and also not bump any of the interferometer mirrors. This is a tight situation and should only be done by people with steady hands!

In STXM IV we used to use a laser in the optics alignment, but haven't done this in a while now. If you want to know more about this procedure please refer to the STXM VI manual , which is still available on our website.

1. Insert the zone plate. Like if taking it out, make sure the exit snout is all the way upstream and you don't bump any of the mirrors. Needless to say, that the sample stage has to be removed (Alignment $\rightarrow$ Edit Alignment $\rightarrow$ Remove Specimen Stage)
2. Insert the VLM (after reinserting the specimen stage), and focus it onto the ZP (see Fig. 12.3).
3. Turn the screws on the ZP kinematic mount with an Allen key, until the ZP appears to be roughly in the center of the exit window (use the marker marks on the monitor as reference). You may preliminarily record the ZP in VLM focus at this point (Alignment $\rightarrow$ Edit Alignment $\rightarrow$ Edit Alignment $\rightarrow$ Record Advanced $\rightarrow$ Record VLM focused on ZP). This will update the parameters vlm_xdet_um, vlm_ydet_um, and vlm_zp_zdet_um in the alignment file (see Sec. 13.1).
4. Move the exit snout downstream, close to the ZP.
5. Now put the pinhole back in as sample, using the vlm move it to where the ZP was on the screen, record it in VLM focus and then do a stepper scan of about 300$\mu$m size. You see the ZP in the illuminated exit window. If the ZP is not centered well (best part of illumination) you need to adjust its position a little (Allen key) and repeat the scan. It may be necessary to do quite a bunch of scans and position corrections in a row.
6. If you did everything right, you should see the focus of the ZP as bright spot in its center. You may need to do a focus scan, to see it well.
7. Retract the specimen, take out the pinhole and insert the VLM focused on the ZP. Now Record ZP in VLM focus and mark its position on the monitor using permanent marker.
8. Remove the sample stage (takes a while) and carefully insert the OSA onto the ZOSA stage. It should snap into place held by magnets.
9. Insert the specimen stage and focus the VLM onto the OSA. Move the OSA in $X$ and $Y$ (Allen key on kinematic mount) to the position, where you marked the ZP on the monitor. Focus again and Record OSA in VLM focus. This will set the proper value of zosa_um in the alignment file (see Sec. 13.1).
10. Insert the pinhole as sample, focus the VLM on it and move the pinhole in $X$ and $Y$, so it comes to lie where you marked ZP and OSA on the monitor. Record Specimen in VLM focus, {textbfInsert Specimen and take a stepper scan.
11. Depending on what the scan looks like, you will probably have to tweak the OSA's $X$ and $Y$ positions. The most likely scenario is, that you see a half donut (which is 3rd order leakage for the ZP) or so and a more or less round spot in the center (1st order focus). Retract Specimen and also move the OSA a little (1mm or so) downstream (careful, if you move upstream instead, you will bump into the ZP!), before you tweak the OSA a little with the Allen key. Repeat scanning and tweaking, until you have nice 1st order focus without leakage from other orders. There other scenarios, of what you might be seeing, but they can't all be described here.
12. Once you are satisfied, with the OSA, focus the VLM again and record it in VLM focus.
13. You now want to properly center the detector onto the x-ray beam. As an example, you might scan XDET and YDET to find the proper $(X,Y)$ position of the detector, and then scan XDET and ZDET to find the proper $Z$ position of the detector. Once you're happy with where the detector is, go to Alignment $\rightarrow$ Edit Alignment $\rightarrow$ Record Advanced and record it as aligned.
14. Now you are ready to put in your first sample (as described in Sec. 2.4) and check if you can get a nice image.

IF the microscope is pretty well aligned and ready for operation, save the alignment with Alignment $\rightarrow$ Write Alignment file.

Figure 12.3: A zone plate as viewed by the VLM.