Hard X-Ray Hartmann Wavefront Sensor for Beamline Optimization

Abstract

Introduction Fourth generation synchrotrons and X-ray free-electron lasers (XFEL) are facilities offering diffraction-limited X-ray beams to a very wide community of users pushing the limits of the science of X-ray-matter interaction. The impacted scientific domain includes life science, biology, chemistry, planetology, solid-state physics, and many others relevant to fundamentals and societal applications. The outstanding beam properties of these new emerging X-ray sources allow scientists to use new experimental techniques such as multi-photon processes and X-ray nonlinear atomic physics, creation of warm dense matter and hot plasma, coherent diffraction imaging and holography, and the study of ultrafast processes. However, these outstanding beams require strong development of X-ray optics and are pushing the demand for versatile and fast at-wavelength metrology. Several technologies have been tested for performing at-wavelength metrology directly on the beamline [1–4]. Hartmann Xray wavefront sensors (HWS) have been used for extreme wavefront precision metrology for today’s most advanced scientific research. HWS can be used to provide real-time measurement of the optical quality of a complex beamline at strategic positions, such as after the monochromator or after any complex optical system. Wavefront aberrations, misalignment of the different optical components, and fluctuations of the position of a focal point can be quantified and characterized. In this article, we will report about measurements of beam qualities at two end-stations, one from fourth generation synchrotrons (ESRF) and one on free electron lasers (European XFEL) [5]. These studies demonstrate the versatility of a compact X-ray Hartmann wavefront sensor, allowing the ability to automatically align focusing X-ray optics such as a compound refractive lens, and to control active optics for optimizing the focal spot.