We derive a model describing the Casimir-Polder interaction between a surface and an extended particle. This method can be used to explain matter-wave interference patterns of large organic molecules diffracting at a grating. We reconstruct the interaction from the interference pattern by additional measurements: the phase information encoded in the matter wave is mapped out by an implementation of Hartmann-Shack sensor for neutral matter waves. Together with tomographic reconstruction of the interaction potential, the polarisability of the interfering particle can be estimated.<eng>
