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.
Highlights
The rapid evolution of hard x-ray free electron laser (FEL) [1,2,3], with femtosecond pulse durations, has enabled a wide range of previously impossible dynamical studies of atoms, molecules, clusters, and materials in the physical and life sciences [4]
For an FEL user, accurate knowledge of the beam delivered to the sample at the interaction point (IP) is critical for planning experiments and interpreting the data collected
As Linac Coherent Light Source (LCLS) operates in a deep saturation regime, FEL simulations generally predict a smaller range of source location fluctuation under nominal operation parameters
Summary
The rapid evolution of hard x-ray FELs [1,2,3], with femtosecond pulse durations, has enabled a wide range of previously impossible dynamical studies of atoms, molecules, clusters, and materials in the physical and life sciences [4]. An x-ray FEL wavefront sensor should provide high sensitivity and accuracy on a single-shot basis, be capable of measurements with both collimated and highly focused beams, survive in a high-power x-ray beam, be robust, and be compatible with in situ analysis and fast wavefront retrieval methods for. Talbot interferometers and their variations, such as multilateral shearing interferometers or modified Hartmann mask interferometers, are widely used at visible [12,13,14,15] and infrared wavelengths [16]. In this work we emphasize optimization for high performance of the sensor on a single-shot basis with an unattenuated full FEL beam, and its applications to systematic studies of FEL beam characteristics at different locations along the beam path
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