Reflection bandwidth and spot size

The reflection or spot bandwidth is the narrow range of wavelengths extracted from the overall, much broader bandpass required to stimulate fully the RLP. It is directly akin to the rocking width in the monochromatic rotating crystal method. 

The overall spot bandwidth is determined by the mosaic spread and horizontal beam divergence (since yH yv)  

The size and shape of the diffraction spots vary across the film. The radial spot length is given by convolution as 

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