At-wavelength Metrology of X-ray Optics at Diamond Light Source

Modern third-generation synchrotron radiation sources provide coherent and extremely bright X-ray beams, but the performance of the optics employed on the beamlines is critical for the X-rays' successful exploitation. The quality of the beam delivered to the sample is limited by the optics' imperfections and misalignment. Though the optics are accurately evaluated in metrology labs equipped with visible-light-based measuring instruments, such ex-situ characterizations do not allow perfect predictions of their beamline performance, since the mechanical and thermal strains imposed by beamline operation cannot be perfectly modelled. In-situ at-wavelength characterization is the natural way to overcome this limitation [1]. In-situ wavefront sensing performed at the optics' operating wavelength (“at-wavelength” metrology) can be used not only to optimize the performance of X-ray optics, but also to correct and minimize the collective distortions of upstream beamline optics (e.g., monochromator, windows, etc.). This issue has become even more critical with the increasing use of active optics on the beamlines on one hand, and with the desire to achieve diffraction-limited and coherence-preserved beams [2] on the other.