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Chapter 4:
Imaging Systems for X Rays
The interaction between radiation and matter is too weak in the far ultraviolet and x-ray regions to allow substantial and efficient deflection of a beam in a single step. Multiple reflections or diffraction from multielement structures are used to increase the efficiency. If the small amplitudes from all subelements are added coherently with equal phase, the efficiency can increase ∝ N2, where N is the number of subelements. However, the subelements have to be fabricated and assembled with high precision and have to be illuminated coherently. Errors in the different possible pathlengths from each part of the structure have to be small compared to the wavelength. When this requirement cannot be met, amplitudes from different parts of a structure are added with random phases. In this case the intensities from all subelements are added; i.e., the efficiency increases ∝N.
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