For some experiments the high resolution of perfect crystals is not required and higher flux is preferred to reduce exposure times and speed data collection. Double multilayer monochromators (DMM) use a matched pair of multilayer optics to select a relatively wide energy bandpass beam from a white beam source.
The ability to select different material combinations and lay down different thicknesses allows a large span of energy ranges from 2-100keV, with energy resolutions from 0.2-3%, whilst maintaining reflectivities of >75%.
Combination monochromators (DCM/DMM) can be used in a single beamline to provide the capability of rapidly switching between high resolution and high flux modes.
Example of multilayer optic with 2 stripes
|Active Optical Area||300mm x 75mm|
|Slope Error||< 1.5 µrad rms|
|Surface Roughness||< 1Å rms|
|Energy Range||2-8 keV||8-20 keV|
|D spacing||45 Å||28 Å|
|Number of periods||> 100||> 150|
|Peak Reflectivity||> 85% at 5 keV|
> 75% at 12 keV
|>90% at 8 keV
>90% at 20 keV