The next generation light sources such as diffraction-limited storage rings and high repetition rate free electron lasers (FELs) will generate x-ray beams with significantly increased peak and average brilliance. These future facilities will require x-ray optical components capable of handling large instantaneous and average power densities while tailoring the properties of the x-ray beams for a variety of scientific experiments. We have been developing diamond x-ray refractive lens for 3 years. Standard deviation of lens residual gradually was decreased to sub-micron values. Post-ablation polishing procedure yields 10-20nm surface roughness, Ra. In this paper we report on recent developments towards beam-line ready optic.
An ongoing collaboration among four US Department of Energy (DOE) National Laboratories has demonstrated key technology prototypes and software modeling tools required for new high-coherent flux beamline optical systems. New free electron laser (FEL) and diffraction-limited storage ring (DLSR) light sources demand wavefront preservation from source to sample to achieve and maintain optimal performance. Fine wavefront control was achieved using a novel, roomtemperature cooled mirror system called REAL (resistive element adjustable length) that combines cooling with applied, spatially variable auxiliary heating. Single-grating shearing interferometry (also called Talbot interferometry) and Hartmann wavefront sensors were developed and used for optical characterization and alignment on several beamlines, across a range of photon energies. Demonstrations of non-invasive hard x-ray wavefront sensing were performed using a thin diamond single-crystal as a beamsplitter.
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. Following successful experiment at LCLS [Seiboth, F. et al. Perfect X-ray focusing via fitting corrective glasses to aberrated optics. Nat. Commun. 8, 14623 doi: 10.1038/ncomms14623 (2017)], where phase plate was etched out of silica, Euclid Techlabs LLC uses femtosecond laser ablation to produce similar phase correctors out of diamond. In this paper we will present several examples along with measurements done at the Advanced Photon Source of Argonne.
This 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.
Compound refractive lenses (CRLs) are widely used as focusing optics at X-ray synchrotron beamlines. For example, the Advanced Photon Source Upgrade (APS-U) beamlines will utilize a large number of CRLs. These lenses must be of high quality to preserve the wavefront and coherence properties of the new source. Therefore, they must be evaluated for quality control and performance before installation and use. At the APS, singlegrating Talbot interferometry has been the primary at-wavelength characterization method because of its high speed, and the ability to provide accurate, quantitative measurements. However, even though the measurement of a single lens is fast, the characterization of a large number of lenses is time consuming due to the time spent on mounting and alignment of individual samples. To adapt the method for testing large quantities of lenses, a fast evaluation system was developed, which includes the use of a lens cartridge for rapid sample change and alignment and an automated python script for batch data analysis. In this work, the optical specifications of refractive lenses are discussed. Measurement and data analysis procedures are also shown in details for testing individual lenses.
Single-grating Talbot imaging relies on high-spatial-resolution detectors to perform accurate measurements of X-ray beam wavefronts. The wavefront can be retrieved with a single image, and a typical measurement and data analysis can be performed in few seconds. These qualities make it an ideal tool for synchrotron beamline diagnostics and in-situ metrology. The wavefront measurement can be used both to obtain a phase contrast image of an object and to characterize an X-ray beam. In this work, we explore the concept in two cases: at-wavelength metrology of 2D parabolic beryllium lenses and a wavefront sensor using a diamond crystal beam splitter.
The current status of the software package PHASE for the propagation of coherent light pulses along a synchrotron
radiation beamline is presented. PHASE is based on an asymptotic expansion of the Fresnel-Kirchhoff integral
(stationary phase approximation) which is usually truncated at the 2nd order. The limits of this approximation as well as
possible extensions to higher orders are discussed. The accuracy is benchmarked against a direct integration of the
Fresnel-Kirchhoff integral. Long range slope errors of optical elements can be included by means of 8th order
polynomials in the optical element coordinates w and l. Only recently, a method for the description of short range slope
errors has been implemented. The accuracy of this method is evaluated and examples for realistic slope errors are given.
PHASE can be run either from a built-in graphical user interface or from any script language. The latter method provides
substantial flexibility. Optical elements including apertures can be combined. Complete wave packages can be
propagated, as well. Fourier propagators are included in the package, thus, the user may choose between a variety of
propagators. Several means to speed up the computation time were tested - among them are the parallelization in a multi
core environment and the parallelization on a cluster.