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 and is currently in the focus of an aggressive R&D undertaken by NSLS-II. In its baseline scope, the forthcoming beamline will provide a 1 meV broad resolution function with sharp, nearly Gaussian, tails 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 pre-monochromatize the beam before it is delivered to the high-resolution monochromator based on a four bounces scheme. 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 CDW analyzer system based on asymmetric dispersive crystal optics. The analyzed radiation is finally recorded by a strip detector. In the mature phase, the high-resolution monochromator will be replaced with the CDDW design, whereas for the analyzer optics, a channel cut crystal will be added after the CDW analyzer to achieve the ultimate 0.1 meV resolution.