Binary Amplitude Reflection Gratings for X-ray Shearing and Hartmann Wavefront Sensors

New, high-coherent-flux X-ray beamlines at synchrotron and free-electron laser light sources rely on wavefront sensors to achieve and maintain optimal alignment under dynamic operating conditions. This includes feedback to adaptive X-ray optics. We describe the design and modeling of a new class of binary-amplitude reflective gratings for shearing interferometry and Hartmann wavefront sensing. Compact arrays of deeply etched gratings illuminated at glancing incidence can withstand higher power densities than transmission membranes and can be designed to operate across a broad range of photon energies with a fixed grating-to-detector distance. Coherent wave-propagation is used to study the energy bandwidth of individual elements in an array and to set the design parameters. We observe that shearing operates well over a +/- 10% bandwidth, while Hartmann can be extended to +/- 30% or more, in our configuration. We apply this methodology to the design of a wavefront sensor for a soft X-ray beamline operating from 230 eV to 1400 eV and model shearing and Hartmann tests in the presence of varying wavefront aberration types and magnitudes.

Automated summary

New binary-amplitude reflective gratings have been designed and modeled for shearing interferometry and Hartmann wavefront sensing in high-coherent-flux X-ray beamlines. These gratings, compact and capable of withstanding high power densities, can operate across a broad range of photon energies with fixed grating-to-detector distance. Coherent wave-propagation is utilized to study energy bandwidth and set design parameters, enabling effective performance over a wide bandwidth.