Alignment of the Zone Plate

For alignment of zone plate and OSA, we use mostly the alignment telescope mounted on the downstream VLM viewport on the chamber. The telescope can be adjusted with 2 sets of 3 screws on a holder.

• Image the entrance window.

  Do a stepper scan of the entrance window with a 5 or 10 micron pinhole. Move the sample to the center of the exit window.

• Align the zone plate.

  Move the zone plate in z until it is only a couple of millimeters from the focus position. You can use the scale on the bottom of the sample stage to do that. There is a mirror plus telescope on top of the chamber, allowing to look into the sample area from above and seeing the relative postions of ZP, OSA, sample (holder) and anticontaminator blades.

  Focus the telescope onto the sample. With the sample pinhole set ot the center of the entrance window, move the cross bar on the telescope as precisely as possible on the pinhole.

  Move the sample 4 or 5 mm up to get it out of the beam. In the telescope, you should see the slightly defocused zone plate wafer. Bring the center of the wafer on the cross hair by moving the zone plate in x and y with the piezo micrometer acuators (piezomikes). Align the center of the window on the cross hair. If done carefully, the window on the zone plate wafer should now overlap in at least a small area with the entrance window.

  Move the sample back on the center-of-window position and confirm that the cross hair is still on the pinhole. If not, repeat the alignment of the zone plate.

  Move in the detector and take an image of the entrance window with the same parameters as before. You should see the overlap of the entrance window with the zone plate window. If not, and you have convinced yourself that you have beam and that the detector is on and in the right position, repeat the alignment precedure with the telescope.

  While taking an image of the zone plate window, roughly center the ZP with the piezomikes on the window.

• Focus the zone plate

  The ZP and OSA can be viewed through a viewport on the top flange which is centered on a hole in the scanning stage on top of the sample. A mirror plus telescope is mounted next to the viewport to enable you to see at the sample area.

  If you do not see a donut pattern (or even a focus) within the central stop area of the zone plate, you are far out of focus. Calculate the focal position. Use the telescope to observe the ZP through the viewport on the top flange and prealign the zone plate using the scale below the sample. Take a new scan. If you still do not see a donut pattern, and you have convinced yourself that gap and monochromator settings are correct, then move the zone plate in z by a distance of several depths of focus. When moving, observe the zone plate through the window on the top flange to avoid crashing the zone plate. Take a new scan. If you still do not see a donut pattern, take a nap and try again later.

  If you see a donut pattern, use a focal scan to focus the zone plate. Always make sure that the z range will not lead the ZP on a collision course with the sample.

  When the zone plate is focused well, do an x/y stepper scan. If necessary, realign the ZP to the center of the entrance window using the piezomikes. Then reconfirm the focal position.