Researchers developed optimized coatings for diffraction gratings at the Advanced Light Source (ALS) that use thin-film interference to double the light reaching the sample, capturing power otherwise lost to absorption.
Every soft x-ray beamline monochromator uses gratings and can benefit from increased diffraction efficiency.
How to win back lost x-rays
Soft x-rays allow us glimpses into the most fundamental properties of many materials by revealing what electrons are doing in a solid. But, the gratings that separate and bend x-rays in these studies struggle to deliver more than a small fraction of an incoming beam’s energy to its target. This has led researchers on a quest to improve the efficiency of gratings, without compromising the resolution of the output data.
Gratings are the key technology for soft x-ray experiments and most spectroscopy tools. Their periodic structures parse light into separate wavelengths, which are then either selected individually or dispersed across a detector. To achieve high resolution, these metal-coated gratings need an extremely high number of closely packed grooves. The grooves, however, are a double-edged sword: they deflect incoming x-rays toward the sample, but some x-rays are absorbed by the coating and cannot usefully contribute.
In this study, researchers sought to win back some of the x-rays that are lost. They examined how very thin metal coatings impacted a grating’s performance. The team, led by ALS Staff Scientist Dmitriy Voronov, tested gratings coated with atoms-thick layers of chromium (Cr) and gold (Au) and showed that an optimized configuration doubled the efficiency compared with standard designs.
Read more on the ALS website
Image: A silicon grating with half a million grooves and coated with atoms-thick layers of chromium and gold will provide higher energy resolution at Advanced Light Source Beamline 6.0.2 QERLIN. QERLIN is a double-dispersion resonant inelastic x-ray scattering (RIXS) beamline.