Focused beam profile measured by dark-field edge scan. Edge scan was carried out with 3.125 nm step and 1 s integration time per point. X-ray energy is 8 keV. An edge of tantalum thin film (0.5 $\mu$m-thick) is used as a knife-edge. Solid circles are measured data, and the red line represents theoretical profile for ideal circular aperture lens. Signal current of ionization chamber is about 2 pA at the peak.