Many hot topics related to the high frequency dynamics of condensed matter require both a narrower and steeper resolution function and access to a broader dynamic range than what are currently available. This represents a sort of “no man’s land” that falls right in the dynamic gap lying between the high frequency spectroscopies, such as inelastic x-ray scattering (IXS), and the low frequency ones. New IXS spectrometers with improved energy and momentum resolutions would be required to fill this gap. To achieve this goal, a new x-ray optics concept for both the monochromatization and energy analysis of x-rays will be implemented at the NSLS-II Inelastic X-ray Scattering beamline. This solution exploits the effect of angular dispersion in asymmetric Bragg diffraction, through the so-called CDW/CDDW arrangements, for which aggressive R&D is currently being undertaken by NSLS-II. We aim to achieve within the baseline scope a 1 meV resolution with a sharp resolution tail and a momentum resolution better than 0.25 nm-1. The setup of this novel spectrometer will benefit many areas of research, including:
In the further development phase of the beamline, we aim to achieve the ultimate goal of a 0.1 meV resolution function and a momentum resolution substantially better than 0.1 nm-1.
The baseline design of the beamline includes a compound refractive lens to pre-focus and a double crystal high heat load monochromator to premonochromatize the beam before it is delivered to the high- resolution CDDW monochromator. The monochromatic beam is then focused by a set of KB mirrors to the sample. A multilayer double (horizontal and vertical) collimating mirror, mounted on the spectrometer arm, allows collecting the beam scattered by the sample with a large angular acceptance and delivers a beam within a divergence low enough to be accepted by the CDDW analyzer system. The analyzed radiation will finally be recorded by a strip detector. In the mature phase, the dispersive elements of the analyzer will be replaced by the so-called comb crystal, and a channel cut crystal will be added after the CDDW monochromator to achieve the ultimate 0.1 meV resolution.