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Monochromatic Doubly Curved Crystal Optics

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Doubly Curved Crystal (DCC) optics offer an enabling technology for emerging portable, remote, and in-situapplications of monochromatic X-ray analysis. Applications include composition and structure analysis of solids and liquids, including amorphous, polycrystalline, and crystalline materials. DCC optics, based on Bragg diffraction, are toroidally-curved crystals for producing three-dimensionally focused, monochromatic X-rays. For this reason DCCs are often referred to as monochromatic X-ray optics. Various crystal materials can be used for DCC optics, including Si, Ge, quartz, graphite, and mica. DCC optics capture a large solid angle of X-Rays from an X-ray tube which are then focused to a small spot. With this point-to-point focusing of X-rays, the achievable spot size is directly related to the spot size of the X-ray tube.

DCC optics are primarily used for X-ray fluorescence applications where monochromatic excitation is required; although the optics can also be used as efficient monochrometers for wavelength dispersive applications. The principal benefit of DCC optics is their ability to produce an intense, highly monochromatic, highly focused X-ray beam in a small spot with a large working distance. Monochromatic excitation eliminates X-ray scattering background under the fluorescence peaks and therefore provides improved measurement sensitivity. Intensities achieved with these optics, when coupled with low-power X-ray sources, are comparable to kW sources such as rotating anodes. Different crystal geometries can be used to optimize desired parameters such as collection solid angle or magnification of the focal spot. For example, asymmetrically-cut point-focusing DCCs are used for (de)magnification; and large rotation DCCs provide high flux in large focal spots. Logarithmic spiral DCCs provide a large collection solid angle.

Characteristics of DCC Optics:

Type Beam Focusing, Monochromatic
Useful X-ray Energy Range Typically 1.5 – 35 keV
Reflectivity 10% to 20%
Collection solid angle 0.01 to 0.1 sr
Convergent angles 1 – 5 degrees x 30-100 degrees
Working Distance 50 – 500 mm
Focused beam size (FWHM) 50 – 500 ђµm (depending on source size, crystal material, and working distance)
Gain (Compared to pinhole aperture 100 mm from source) 1000x (depending on optic design)