Phase Correction Plates for X-Rays

X-ray focusing optics, irrespective of the technology employed, require extremely high precision of both manufacturing and metrology, and also require in-use operational stability. As the x-ray beam is being transported to the experimental area, distortions due to misalignments, the imperfection of optics, and other effects will accumulate and result in beam quality degradation—spatial broadening, and the appearance of beam tails and aberrations. Recently, it became possible, using ptychography methods, to quantify cumulative beam phase distortion. Based on these measurements, a single element of refractive optics, a phase correction plate, can be designed to correct for this cumulative beam degradation. Euclid Techlabs LLC proposes to use femtosecond laser ablation to produce such phase correctors rapidly and at low cost. Such “disposable” optics can be designed on the fly, and promptly manufactured for a specific beamline configuration and x-ray energy. In Phase I, we will developed several algorithms for complex surfaces ablation. High shape accuracy had been achieved. As ablated surface roughness of 1-2 microns r.m.s. is higher than acceptable for x-ray optics. Polishing of a phase plate had been attempted. For cylindrically symmetric shapes the required 100nm surface roughness and even better can be achieved by in-house technique that involves a polishing spindle that conforms with cylindrical symmetry. When the shape does not have such symmetry polishing with spinning bit distorts the phase plate shape. Phase I concluded with a test at the Advanced Photon Source (APS) of Argonne where one phase plate was used to distort the x-ray beam and the second phase plate corrected the phase front of the x-ray beam. In Phase II, we utilize a polishing procedure with random motion of the polishing bit. Based on Phase I results the polishing rate has to be decreased significantly in order to preserve a few microns peak to valley shape while decreasing local surface roughness from 1-2 microns r.m.s. down to 100 nm. We are actively collaborating with X-Ray Optics Group at APS. In phase II we plan to produce o demand phase plates for calibrated beamline. The proposed approach is plug and play, and can be employed in a large number of x-ray beamlines around the world. The ability to synthesize and rapidly produce a phase-correcting plate is a paradigm shift in the design of x-ray optics systems. Rather than require unprecedented fabrication tolerance, for example, for x- ray mirrors, while simultaneously managing thermal effects like non-uniform expansion due to the x-ray flux, one can focus on thermal stability while employing a simpler geometry, and use a complimentary phase plate that will correct the imperfections of the mirror. This technology will increase the quality of the x-ray beam and simplify beam delivery and alignment.