NSLS-II Seminar

A central issue in IXS spectrometer design is achieving high resolution with a compact design. Present meV resolution spectrometers typically have two-theta arms that are ~10 m length. The recent introduction of "dispersion compensation" [1] showed it was possible to use a position sensitive detector to improve the resolution using a short spectrometer arm operating with ~10 meV resolution. However this concept at a cost of severe reduction in the sample space, which becomes prohibitive for higher resolution.

We introduce a new spectrometer concept [2] that allows large sample space with high resolution and a relatively short arm. The essential idea is to add a temperature gradient across the analyzer. This compensates for chromatic aberrations that are introduced when the detection point is moved off the Rowland circle. Investigations using both analytical approximations and detailed ray-tracing shows it is possible to make a ~1.5 meV resolution spectrometer using a ~3 m while leaving ~200 mm free space near the sample. In medium resolution, 10-100 meV, setups, this method may also be used to make large gains in space near the sample position for a given resolution. This method may also be used to improve energy resolution with a single element detector, and can allow improved momentum resolution without slitting analyzer crystals.

[1] S. Huotari, et al (2005). J Synchrotron Rad. vol.12, 467-472 [2] D. Ishikawa and A. Q. R. Baron, Submitted.