Abstract
We report on the design, implementation, and performance of an x-ray monochromator with ultra-high energy resolution (ΔE/E ≃ 2.7 × 10(-8)) and high spectral efficiency using x rays with photon energies E ≃ 9.13 keV. The operating principle of the monochromator is based on the phenomenon of angular dispersion in Bragg back-diffraction. The optical scheme of the monochromator is a modification of a scheme reported earlier [Shvyd'ko et al., Phys. Rev. A 84, 053823 (2011)], where a collimator/wavelength selector Si crystal was replaced with a 100-μm-thick type IIa diamond crystal. This modification provides a very-small-energy bandwidth ΔE ≃ 0.25 meV, a 3-fold increase in the aperture of the accepted beam, a reduction in the cumulative angular dispersion rate of x rays emanating from the monochromator for better focusing on a sample, a sufficient angular acceptance matching the angular divergence of an undulator source (≈ 10 μrad), and an improved throughput due to low x-ray absorption in the thin diamond crystal. The measured spectral efficiency of the monochromator was ≈ 65% with an aperture of 0.3 × 1 mm(2). The performance parameters of the monochromator are suitable for inelastic x-ray spectroscopy with an absolute energy resolution ΔE < 1 meV.
Highlights
High-resolution x-ray monochromators for hard x-rays (E 10 − 20 keV) with energy bandwidths ∆E 1 − 0.1 meV are indispensable tools for inelastic x-ray scattering (IXS) spectroscopy [1,2,3], nuclear resonant scattering spectroscopy [4, 5], ultra-precise crystal lattice parameter measurements [6,7,8], x-ray interferometry [9], x-ray metrology, and for other applications in x-ray science
The monochromator is designed for applications in ultra-high-resolution IXS; it can be used in other research fields as well
In this work we show that design of angular dispersive (AD) optics can be optimized to yield x-ray monochromators with an unmatched performance in terms of spectral efficiency and energy resolution characteristics
Summary
High-resolution x-ray monochromators for hard x-rays (E 10 − 20 keV) with energy bandwidths ∆E 1 − 0.1 meV are indispensable tools for inelastic x-ray scattering (IXS) spectroscopy [1,2,3], nuclear resonant scattering spectroscopy [4, 5], ultra-precise crystal lattice parameter measurements [6,7,8], x-ray interferometry [9], x-ray metrology, and for other applications in x-ray science. We present a hard x-ray monochromator with a unique combination of a very small 0.25-meV bandwidth, a very high 65% efficiency, and steep spectral tails. Angular dispersive x-ray optics can achieve sub-meV bandwidths, a very large angular acceptance of 100 μrad, and steep tails of the spectral functions. In this work we show that design of AD optics can be optimized to yield x-ray monochromators with an unmatched performance in terms of spectral efficiency and energy resolution characteristics. The demonstrated efficiency and superior spectral properties render AD x-ray monochromators perfectly suitable for IXS with very-high-energy resolution.
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