We consider the specification of hard x-ray monochromator crystals for both high-efficiency and diffraction-limited optical performance in the new era of ultra-high-brightness x-ray light sources. Within a double-crystal monochromator, thermal distortions resulting from intense beams can significantly affect the wavefront quality and reduce the total transmitted power. In two case studies, we model the performance of a water-cooled and a cryogenically-cooled monochromator on a working protein crystallography beamline at the Advanced Light Source. The cryo-cooling model appears capable of exceeding diffraction-limited performance specifications while preserving over 99% of the optimal transmitted power. The water-cooled system may perform well for beamlines that are not brightness-limited but does not come close to achieving this high-performance goal.
In this paper we report on the modeling and characterization of transmission windows for in-situ interferometric measurements of cryogenically cooled mirrors. Specifically, we present a model of the temperature distribution and strain in the transmission window, and the corresponding spatial dependence of the window’s index of refraction. We also present experimental results which characterize the effect of the windows on interferometric measurement.
The thorough realization of the advantages of the new generation x-ray light sources, such as the Upgraded Advanced Light Source (ALS˗U) under construction, requires near-perfect x-ray optics, capable of delivering light without significant degradation of brightness and coherence. The stringent requirements of beamline optics drive the state of the art in ex situ optical metrology. Here, we present the results of the ongoing efforts at the ALS X-Ray Optics Laboratory to develop a new generation long trace profiler, LTP-2020. We discuss the system design that incorporates different types of surface slope sensors. In addition to the classical pencil beam interferometry (PBI) sensor with an improved optical design, we develop a deflectometry sensor based on a customized electronic autocollimator (AC). By applying a new data processing algorithm to the AC raw image data available from the customized AC, we significantly reduce the quasi-periodic systematic error of the AC equipped with a small size aperture. We also treat the possibility to use the AC as a PBI sensor with external light beam sources based on super-luminescent emitting diode (SLED) and single-mode laser diode (SMLD). Operation modes with stationary and/or translated sensors are possible due to the two-carriage gantry system with adjustable vertical position. The variety of the available operation modes allows optimization of the LTP-2020 experimental arrangement for providing the best possible performance in measurements with state-of-the-art aspherical x-ray optics, variable-line-spacing diffraction gratings, and multi-element optical systems.
The upgrade of the Advanced Light Source at Lawrence Berkeley National Lab to a Diffraction-Limited Storage Ring (DLSR) will feature four new and upgraded beamlines, designed to take full advantage of the coherence and high brightness of the insertion device source operating mostly in the soft x-ray regime (100–2000 eV). The round and highly coherent beam drives specific design choices for the photon transport optics and monochromator, and technical challenges in terms of performances, optical tolerances and stability. We have used the simulation tools Shadow (for raytracing) or SRW (wavefront propagation), and their implementation in OASYS and Sirepo to refine tolerance specifications, using their scripting capabilities and new add-ons to perform a comprehensive beamline analysis and confirm that specifications matched our performance requirements, taking into account partial coherence and issues related to heatload.
In this paper we provide an update on the development of a novel cantilevered-liquid-nitrogen-cooled-silicon mirror for a new insertion device beamline included in the Advanced Light Source Upgrade (ALS-U). The goals of this mirror development are to achieve diffraction limited performance, demonstrate reliability, minimize coolant flow induced vibration, and demonstrate carbon contamination prevention and cleaning techniques. In this paper we summarize the design requirements, the design of the mirror system, and prototype fabrication.
We describe the implementation of realistic, adaptive wavefront correction in high-brightness beamline simulations to study the correction of thermal deformation. Several planned soft x-ray and tender x-ray insertion-device beamlines in the Advanced Light Source upgrade, where wavefront preservation is paramount, rely on a common design principle.After studying the performance of a 20-channel adaptive x-ray mirror prototype, at-wavelength and with visible-light, we implemented mirror shape-control algorithms in software that are designed to restore and optimize the focused beam intensity (i.e. Strehl ratio), considering the incident wavefront’s phase and amplitude. We implemented the modeling in OASYS which is an adaptable, customizable beamline modeling platform well suited to study this issue.
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