Modular Bimorph Mirrors: From an Established Hardware Design to First Experimental Results Towards Wavefront Correction in the X-ray Domain

Abstract

X‐ray piezoelectric bimorph mirrors, pioneered at the ESRF in the 90’s and subsequently optimized at Spring‐8 in the 00’s, have nowadays reached full maturity. The most recently manufactured devices not only achieved state‐of‐the‐art optical results at the beamline but also gave a clear indication of the still untapped potential that these devices have to realize X‐ray adaptive optics. By using their unique capability to locally steer sub‐segments of the reflective surface (adaptive zonal control), a 300 mm long bimorph could be shaped to an arbitrary surface described by a 9th order polynomial with residual shape errors as small as 100 Å rms over its full optically active length. Results recently obtained at the APS demonstrate the ability of bimorph mirrors to obtain sharp, very high‐contrast focused beams even when the incoming X‐ray wavefront is heavily distorted: a 8.5 (H) × 5.0 (V) μm2 FWHM doubly focused focal spot could be achieved at 33.6 keV. Previous data collected at Spring‐8 had already demonstrated the extreme sharpness of the focused beam when the incoming wavefront is an undistorted spherical wave. In both cases the bimorph mirrors were illuminated over their full optical length and a large focusing distance of 1 m could be used.