32
R. Rüffer and A. I. Chumakov
Fig. 1.11 Schematic layout of the nuclear resonance beamline (ID 18) at the ESRF. FE—front
end; UNDs—three revolver type undulators with periods λ u of 20 and 27 mm; OH1, OH2—optics
hutches, EH1, EH2, and EH3—experimental hutches, CRL—focusing and collimating compound
refractive lenses, S1, S2, and S3—slit systems, HHLM—Si (111) high heat-load monochromator,
HRMs—high-resolution monochromators, SMS—synchrotron Mössbauer source, FM—focusing
monochromator, DIFF—DIFFractometer, UHV—set-up for in-situ preparation, characterization
and NRS measurements of surfaces, interfaces, and nano-structures, CRYO—CRYOmagnet system,
BSM—backscattering monochromator
1.6.1 X-Ray Optics
Nuclear level widths are in the range of neV to μeV (e.g. 4.66 neV for
57 Fe), whereas
energy bandwidths of SR from undulators are in the range of 100 eV. That immediately makes clear that dedicated and optimized SR sources and excellent x-ray optics
are needed to achieve not only highest brilliance but also highest flux. Nowadays, xray optics for NRS applications ranges from eV resolution, via meV resolution, and
eventually to neV resolution, i.e., spanning more than eleven orders of magnitude.
The needed resolution is on the one side determined by the spectroscopy (e.g. NIS)
and on the other side by the demand not to overload the detector system (e.g. NFS).
1.6.1.1 High Resolution Monochromator
For sub-meV resolution, mandatory e.g. for phonon spectroscopy, in-line silicon
high-resolution monochromators based on the ‘nested design’ [96] or the fluxoptimized design [97] are common practice. They may be tailored with high efficiency for energies below about 30 keV.
Figure 1.12 left panel displays the nested-design consisting of two channel-cut
high-quality Si crystals, which are mounted in a nested geometry. Asymmetric cuts
and a proper choice of reflections assure high throughput and fixed and high energy
resolution.
The adopted scheme of the flux-optimized HRM is shown in Fig. 1.12 right panel.
Actually, at the ESRF, we have implemented, as shown in the figure, two of those
HRMs next to each other on one mechanics, each consisting of four flat Si single
crystals, which offer 0.5 and 2 meV resolution just by a horizontal translation of the
R. Rüffer and A. I. Chumakov
Fig. 1.11 Schematic layout of the nuclear resonance beamline (ID 18) at the ESRF. FE—front
end; UNDs—three revolver type undulators with periods λ u of 20 and 27 mm; OH1, OH2—optics
hutches, EH1, EH2, and EH3—experimental hutches, CRL—focusing and collimating compound
refractive lenses, S1, S2, and S3—slit systems, HHLM—Si (111) high heat-load monochromator,
HRMs—high-resolution monochromators, SMS—synchrotron Mössbauer source, FM—focusing
monochromator, DIFF—DIFFractometer, UHV—set-up for in-situ preparation, characterization
and NRS measurements of surfaces, interfaces, and nano-structures, CRYO—CRYOmagnet system,
BSM—backscattering monochromator
1.6.1 X-Ray Optics
Nuclear level widths are in the range of neV to μeV (e.g. 4.66 neV for
57 Fe), whereas
energy bandwidths of SR from undulators are in the range of 100 eV. That immediately makes clear that dedicated and optimized SR sources and excellent x-ray optics
are needed to achieve not only highest brilliance but also highest flux. Nowadays, xray optics for NRS applications ranges from eV resolution, via meV resolution, and
eventually to neV resolution, i.e., spanning more than eleven orders of magnitude.
The needed resolution is on the one side determined by the spectroscopy (e.g. NIS)
and on the other side by the demand not to overload the detector system (e.g. NFS).
1.6.1.1 High Resolution Monochromator
For sub-meV resolution, mandatory e.g. for phonon spectroscopy, in-line silicon
high-resolution monochromators based on the ‘nested design’ [96] or the fluxoptimized design [97] are common practice. They may be tailored with high efficiency for energies below about 30 keV.
Figure 1.12 left panel displays the nested-design consisting of two channel-cut
high-quality Si crystals, which are mounted in a nested geometry. Asymmetric cuts
and a proper choice of reflections assure high throughput and fixed and high energy
resolution.
The adopted scheme of the flux-optimized HRM is shown in Fig. 1.12 right panel.
Actually, at the ESRF, we have implemented, as shown in the figure, two of those
HRMs next to each other on one mechanics, each consisting of four flat Si single
crystals, which offer 0.5 and 2 meV resolution just by a horizontal translation of the