The X-ray Microscope at ASTRID

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Microscopy in the soft X-ray region is done in a similar way as microscopy with visible light or electrons. In contrast to these techniques the properties of the interaction of X-rays with matter and the wavelength of the X-rays allow a resolution below 25 nm for the observation of objects with a thickness of up to 10 micrometer. In particular, objects in an aqueous medium can be investigated. X-rays produced in a bending magnet of the ASTRID synchrotron are focused by a condenser lens into the object region. An objective lens forms a magnified image of the object onto a CCD detector.

Schematic diagram of the Aarhus X-ray microscope

In X-ray microscopy the optics cannot operate by using the effects of refraction or reflection. Fresnel zone plates based on diffraction are employed instead. These circular gratings have a varying line density. With an increasing distance from the centre the gratings become smaller and smaller, therefore producing an increasing angle of diffraction. If the width of the gratings follows a certain rule, an incoming plane wave is focused into different focal points connected to the different orders of diffraction. For a single order the properties of a zone plate are comparable to that of a lens based on refraction.

Last Modified 13 June 2009