Correction of the X‐ray wavefront from compound refractive lenses using 3D printed refractive structures

A refractive phase corrector optics is proposed for the compensation of fabrication error of X‐ray optical elements. Here, at‐wavelength wavefront measurements of the focused X‐ray beam by knife‐edge imaging technique, the design of a three‐dimensional corrector plate, its fabrication by 3D printing, and use of a corrector to compensate for X‐ray lens figure errors are presented. A rotationally invariant corrector was manufactured in the polymer IP‐S TM using additive manufacturing based on the two‐photon polymerization technique. The fabricated corrector was characterized at the B16 Test beamline, Diamond Light Source, UK, showing a reduction in r.m.s. wavefront error of a Be compound refractive Lens (CRL) by a factor of six. The r.m.s. wavefront error is a figure of merit for the wavefront quality but, for X‐ray lenses, with significant X‐ray absorption, a form of the r.m.s. error with weighting proportional to the transmitted X‐ray intensity has been proposed. The knife‐edge imaging wavefront‐sensing technique was adapted to measure rotationally variant wavefront errors from two different sets of Be CRL consisting of 98 and 24 lenses. The optical aberrations were then quantified using a Zernike polynomial expansion of the 2D wavefront error. The compensation by a rotationally invariant corrector plate was partial as the Be CRL wavefront error distribution was found to vary with polar angle indicating the presence of non‐spherical aberration terms. A wavefront correction plate with rotationally anisotropic thickness is proposed to compensate for anisotropy in order to achieve good focusing by CRLs at beamlines operating at diffraction‐limited storage rings.