How to find and record the X-ray focus

We assume that you have prefocused your sample with the VLM (Sec. 2.4, and so you should be within 100 microns of the X-ray focus.

• Take an overview scan and locate a clearly visible feature with a sharp edge. Move to this edge.

• Take a horizontal or vertical focus scan (predefined scans under Scan in the menubar of the SM_GUI main window). At first, you might want to take a rather coarse scan (large steps in X and Z) unless you are already focused quite well.

• Locate the focus, click on it and press the button Move scan devices to mouse.

• Repeat the two steps above with finer scan steps until you are focused well. In the end, the X or Y step size should be smaller than the resolution of the focusing zone plate (on the order of 40nm), and the Z step size should be smaller than the depth of focus (which is on the order of 1micron).

• Record the focus with Alignment $\rightarrow$ Edit Alignment $\rightarrow$ Record specimen in X-ray focus (NOT the VLM focus!!!).
• Save the alignment file with Alignment $\rightarrow$ Write Alignment File, in case you get thrown out from or exit the program.