Each point on the surface can be approximated by an outgoing spherical wave (away from the surface). These waves have solutions such as <math>\boldsymbol{E} = \boldsymbol{E_0} e^{i \left( \boldsymbol{k \cdot x} - \omega t \right)}</math>
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Each point on the surface can be approximated by an outgoing spherical wave. [[Image:huygensprinciple.gif|thumb|Huygen's Principle Illustrated (courtesy of http://www.mathpages.com/home/kmath242/kmath242.htm]] Depending on the nature of the surface topology, the shape will be contained in these outgoing spherical waves, but will diffuse over some distance.
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In our model of the diamond surface, Huygen's principle can be used to determine the forward distance from the surface when the reflected light will no longer contain a ''valid'' image of the surface. Using the diagram at right, [[Image:ResDiagram1.jpg|thumb|Surface Schematic]] and some knowledge of the experimental setup, a rought estimate for the forward distance ''L'' can be calculated using a small angle approximation for the angle.