  The Fourier transform method can be applied to obtain electromagnetic knots,
which are solutions of Maxwell equations in vacuum with non-trivial topology of
the field lines and especial properties. The program followed in this work
allows to present the main ideas and the explicit calculations at undergraduate
level, so they are not obscured by a more involved formulation. We make use of
helicity basis for calculating the electromagnetic helicity and the photon
content of the fields.
