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Achieving diffraction‐limited performance in fourth‐generation synchrotron radiation sources demands monochromator crystals that can preserve the wavefront across an unprecedented extensive range. There is an urgent need for techniques of absolute crystal diffraction wavefront measurement. At the Beijing Synchrotron Radiation Facility (BSRF), a novel edge scan wavefront metrology technique has been developed. This technique employs a double‐edge tracking method, making diffraction‐limited level absolute crystal diffraction wavefront measurement a reality. The results demonstrate an equivalent diffraction surface slope error below 70 nrad (corresponding to a wavefront phase error of 4.57% λ) r.m.s. within a nearly 6 mm range for a flat crystal in the crystal surface coordinate. The double‐edge structure contributes to exceptional measurement precision for slope error reproducibility, achieving levels below 15 nrad (phase error reproducibility < λ/100) even at a first‐generation synchrotron radiation source. Currently, the measurement termed double‐edge scan (DES) has already been regarded as a critical feedback mechanism in the fabrication of next‐generation crystals. [ABSTRACT FROM AUTHOR]

The ever‐increasing brightness of synchrotron radiation sources demands improved X‐ray optics to utilize their capability for imaging and probing biological cells, nano‐devices and functional matter on the nanometre scale with chemical sensitivity. Hard X‐rays are ideal for high‐resolution imaging and spectroscopic applications owing to their short wavelength, high penetrating power and chemical sensitivity. The penetrating power that makes X‐rays useful for imaging also makes focusing them technologically challenging. Recent developments in layer deposition techniques have enabled the fabrication of a series of highly focusing X‐ray lenses, known as wedged multi‐layer Laue lenses. Improvements to the lens design and fabrication technique demand an accurate, robust, in situ and at‐wavelength characterization method. To this end, a modified form of the speckle tracking wavefront metrology method has been developed. The ptychographic X‐ray speckle tracking method is capable of operating with highly divergent wavefields. A useful by‐product of this method is that it also provides high‐resolution and aberration‐free projection images of extended specimens. Three separate experiments using this method are reported, where the ray path angles have been resolved to within 4 nrad with an imaging resolution of 45 nm (full period). This method does not require a high degree of coherence, making it suitable for laboratory‐based X‐ray sources. Likewise, it is robust to errors in the registered sample positions, making it suitable for X‐ray free‐electron laser facilities, where beam‐pointing fluctuations can be problematic for wavefront metrology. [ABSTRACT FROM AUTHOR]