  The orbital angular momentum conservation of light reveals different
diffraction patterns univocally dependent on the topological charge of the
incident light beam when passing through a triangular aperture. It is
demonstrated that these patterns, which are accessed by observing the far field
measurement of the diffracted light, can also be obtained using few photon
sources. In order to explain the observed patterns, we introduce an analogy of
this optical phenomenon with the study of diffraction for the characterization
of the crystal structure of solids. We demonstrate that the finite pattern can
be associated to the reciprocal lattice obtained from the direct lattice
generated by the primitive vectors composing any two of the sides of the
equilateral triangular slit responsible for the diffraction. Using the relation
that exists between the direct and reciprocal lattices, we provide a conclusive
explanation of why the diffraction pattern of the main maxima is finite. This
can shed a new light on the investigation of crystallographic systems.
