The ultrahigh energy resolution IXS spectrometer being developed at the National Synchrotron Light Source II (NSLSII)
employs an innovative optical design. Its analyzer system utilizes an L-shaped laterally graded multilayer mirror in
tandem with a multi-crystal arrangement. The multi-crystal arrangement explores the angular dispersion effect in
extremely asymmetric Bragg reflections to achieve sub-meV energy resolution at an energy about 9.1 keV. Its angular
acceptance (~ 0.1 mrad) is about two orders of magnitude lower than the spherically-bent backscattering analyzers
conventionally used in other IXS spectrometers. The L-shaped laterally graded multiplayer mirror was designed to
increase the angular acceptance of this new multi-crystal optics to a comparable level. It performs angular collimation of
the incoming beam from about 15 mrad down to 0.1 mrad in both vertical and horizontal directions. Here we present
simulations of the mirror performance and study the positioning and stability requirements in conjunction with the multicrystal
energy analyzer.
Theoretical analysis of high-energy-resolution x-ray optics, such as backscattering and four-bounce monochromators
and analyzers, has been carried out using computer modeling within the framework of the dynamical theory of x-ray
diffraction. This analysis identifies several important techniques for the precise alignment and determination of the
energy and bandwidth of the monochromators. The destructive contribution of multiple-wave diffraction to the scattering
intensity of x-ray backscattering optics has also been analyzed in details. An important method has been identified which
allows this destructive contribution to be avoided.
Over the past three years NASA Marshall Space Flight Center has been collaborating with Brookhaven National
Laboratory to develop a modular Silicon Drift Detector (SDD) X-Ray Spectrometer (XRS) intended for fine surface
mapping of the light elements of the moon. The value of fluorescence spectrometry for surface element mapping is
underlined by the fact that the technique has recently been employed by three lunar orbiter missions; Kaguya,
Chandrayaan-1, and Chang'e. The SDD-XRS instrument we have been developing can operate at a low energy threshold
(i.e. is capable of detecting Carbon), comparable energy resolution to Kaguya (<150 eV at 5.9 keV) and an order of
magnitude lower power requirement, making much higher sensitivities possible. Furthermore, the intrinsic radiation
resistance of the SDD makes it useful even in radiation-harsh environments such as that of Jupiter and its surrounding
moons.
Absolute spectroscopic photocurrent calibration of detectors in the photon energy range of 50-6000 eV is performed at
beamlines U3c and X8a of the National Synchrotron Light Source at Brookhaven National Laboratory. These beamlines
are specifically designed to provide high flux over a wide energy range, with particular attention paid to harmonic purity
of the monochromatic beam. Examples of optics which enhance the beam purity include transmission foils and grazing-incidence
mirrors. The AXUV-100G silicon photodiode available from IRD is used as a reference detector. Its
relatively simple design, and the availability of x-ray optical data for silicon and silicon dioxide, permit application of
the "self-calibration" method of estimating absolute response, typically to 2% accuracy or better. Characteristics of
typical such diodes will be described, including spectroscopic responsivity and models, lot matching, electrical
characteristics, visible and infrared light responsivity, and soft x-ray photon-induced damage.
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