Because the MFM scans a space devoid of sources of magnetic field, in practice we can write the latter as the gradient of a magnetic potential, , where  satisfies the Laplace equation. For definiteness we assume the sources of the stray field (provided by the sample) are described by a boundary condition on the xy-plane, parallel to the scan plane located at distance z from the top surface of the sample. In the 2D Fourier space utilized in the previous section, this leads to the convenient expression

and therefore also to