High-accuracy wavefront sensing for x-ray free electron lasers

Abstract

Systematic understanding and real-time feedback capability for x-ray free electron laser (FEL) accelerator and optical components are critical for scientific experiments and instrument performance. Single-shot wavefront sensing enables characterization of the intensity and local electric field distribution at the sample plane, something that is important for understanding scientific experiments such as nonlinear studies. It can also provide feedback for alignment and tuning of the FEL beam and instrumentation optics, leading to optimal instrument performance and greater operational efficiency. A robust, sensitive, and accurate single-shot wavefront sensor for x-ray FEL beams using single grating Talbot interferometry has been developed. Experiments performed at the Linac Coherent Light Source (LCLS) demonstrate 3σ sensitivity and accuracy, both better than λ∕100, and retrieval of hard x-ray (λ 0.13 nm, E 9.5 keV) wavefronts in 3D. Exhibiting high performance from both unfocused and focused beams, the same setup can be used to systematically study the wavefront from the FEL output, beam transport optics, and endstation focusing optics. This technique can be extended for use with softer and harder x rays with modified grating configurations.

Correction of the X-ray wavefront from compound refractive lenses using 3D printed refractive structures

“…Nano-and micro-fabrications have played a pivotal role in the development of novel micro X-ray optical elements which led to a significant advance in achieving nano-and micrometre-size focused X-ray beams (Li et al, 2020;Dhamgaye et al, 2014;Lyubomirskiy, Boye et al, 2019;Yan et al, 2014). Highly sensitive X-ray optical measurements, especially sensitive wavefront error measurements, were possible due to microfabrication of 1D and 2D X-ray gratings (Liu et al, 2018;Weitkamp et al, 2005;Rutishauser et al, 2012). Lithography techniques including Si etching, X-ray lithography and laser ablation were used in the development of nano-focusing lenses and wavefront corrector plates.…”

Observation of Seeded Mn Kβ Stimulated X-Ray Emission Using Two-Color X-Ray Free-Electron Laser Pulses

“…The stochastic nature of the SASE seed pulse and the tight requirements for spectral, temporal and spatial overlap lead to a large variation in seeded Kβ S-XES signals even for identical population inversions. Much improved spectral and temporal pulse diagnostic and control [39,40] will remove many of these uncertainties in the future. Shot-by-shot diagnostics of the seed pulse will make it possible to separate the seeded Kβ S-XES signal from the seed pulse.…”

Pulse-to-pulse wavefront sensing at free-electron lasers using ptychography

“…There exist a few key differences between ptychographic wavefront characterization and grating-based methods (Schneider et al, 2018;Liu et al, 2018). The latter can be used for online characterization and, for instance, can provide information on the same wavefronts used for imaging experiments.…”

“…However, with ultra-short pulses (down to femtoseconds) which can reach a flux sufficient to destroy or irreversibly damage most targets, these methods mostly provide only partial information about the wavefront, such as position, size, shape, intensity or curvature (Chalupsky et al, 2011;Vartanyants et al, 2011;Rutishauser et al, 2012;Loh et al, 2013;Sikorski et al, 2015;Keitel et al, 2016;Daurer et al, 2017). A recent grating-based method can provide real-time wavefront distributions (Schneider et al, 2018;Liu et al, 2018), though away from the focal plane and with a resolution limited by the grating's manufacturing process.…”