X-ray nanofocusing using a piezoelectric deformable mirror and at-wavelength metrology methods

An adaptive X-ray mirror with shape controllability in a spatial wavelength range longer than 20 mm was developed, and we demonstrated its shape generation and focusing performance characteristics. The shape accuracy in a spatial wavelength range shorter than 20 mm, which cannot be adaptively figured, was controlled in advance offline. A pencil beam method for measuring the slope error and a phase retrieval method for precisely estimating the wavefront error were employed for online shape correction. A focal spot size of 120 nm, which is diffraction-limited, was realized, and the shape accuracy obtained nearly satisfied Rayleigh's quarter-wavelength criterion.