Alignment of the OSA

Center the sample pinhole on the focal spot. View the OSA through the top window and roughly pre-align it in z. Move the detector out of the way.

• For large OSA's ($70 \mu m$ or so) or if you are using one of the strip apertures where the position of the pinhole can be estimated quite well, you might want to try alignment with the telescope. This should be done only if you are fairly confident about the right z position of the OSA.

  Focus the alignment telescope on the sample. Place the cross bar as well in the center of the sample as possible. Move the sample out in y. Now move the OSA with the piezo mikes until the pinhole is on the crossbar. Place the sample back in and scan the area around the focal spot. If you see some transmitted flux, you can do the fine alignment with the piezo mikes. If you do not see any x-rays, do the alignment with the VLM.

• Alignment of the OSA with the visible light microscope

  (Unfortunately, we don't always have the VL lens installed ...)

  Move the 5$\times$ lens into position. Focus the VLM on the sample using the x/y/z micrometer stage. Place the central square of the VLM on the pinhole position. Record x, y, and z reading

  Move the sample out in y. Focus the VLM on the center of the zone plate. Record x, y, z.

  Calculate the distance between ZP and OSA. Calculate the deviation of the x and y position of the sample from the x and y position of the zone plate (The deviation is due to misalignment of the detector stage). Using the z distance of ZP and OSA, calculate the x and y position of the OSA.

  Move the VL lens to the required z position. Correct the x and y position according to your calculation.

  Move the OSA into the field of view. Bring the OSA into focus by moving it with the piezomikes in z. Align x and y with the piezomikes.

  The OSA should now be close to focus. Move the sample in and take an image of the area around the focal spot.When you see transmitted flux, do the fine alignment of the OSA with the piezomikes in the usual way. If there is no flux, make sure that there is beam in the ring, that all valves are open and that the detector is in position and turned on. If there is still no flux, repeat the procedure above.

  [Unfortunately, the piezomikes frequently exhibit cross talk, which can make tweaking the OSA very tedious.]

Now, zone plate and OSA are aligned. Make sure to turn the knob on the piezomike controller to number 7 or 8; this ensures that the piezomikes cannot move even if the hand pad gets actuated by mistake. You can then switch to the test pattern or sample and take your images.