Wavefront Closed-Loop Correction for X-Ray Microfocusing Active Optics

Automatic alignment of a synchrotron beamline by Hartmann technique was performed, in the soft X‐ray range (E = 3 keV, λ = 0.414 nm), using a 4‐actuators Kirkpatrick‐Baez (KB) active optic. A system imaging the KB focal spot and a soft X‐ray Hartmann wave‐front sensor were used alternatively to control the KB. The beam corrected with the help of the imaging system was used to calibrate the wave‐front sensor. With both closed loops, we focused the beam into a 6.8×9 μm2 FWHM focal spot. Closed‐loop corrections are limited by the optical quality of the imaging system.