1. A method for optically inspecting a sample, the method comprising: obtaining empirical optical response information describing the diffraction resulting from the interaction of a probe beam with the sample; defining a model for the sample, where the model includes one or more control points, the control points collectively defining the cross-sectional profile of at least one layer within the sample; evaluating the model to obtain calculated optical response information predicting the diffraction resulting from the interaction of the probe beam with the sample; and comparing the empirical optical response information and the calculated optical response information to determine the accuracy of the model.