Fig. 1. Schematic of the confocal X-ray instrument

Fig. 2. (a) An iron wire stick on a paper by scotch tape used to measure the confocal volume; (b) Zoomed image of the iron wire captured by a digital microscope

Fig. 3. Process of the overlapping the iron wire and the confocal volume of the confocal X-ray instrument

Fig. 4. Two-dimensional scanning-path of the confocal volume by the metal wir

Fig. 5. Intensity distribution of the Cu-Kα of Y-Z plane of the confocal volume

Fig. 6. Intensity distribution of the Cu-Kα of X-Z plane of the confocal volume

Fig. 7. Diameter of the confocal volume in X, Y and Z direction at different energy