We study square and triangular optical lattice formation using a diffraction technique with light-possessing orbital angular momentum (OAM). We demonstrate that it is possible to use Fraunhofer diffraction of light by a square aperture to unveil OAM about two times bigger than would be possible with a triangular aperture. We notice that the pattern remains truncated until a topological charge (TC) equal to 20 with good precision. Even though a square pattern cannot be used to determine the TC sign, it is possible to measure high order of the modulus and sign of the TC up to 20, combining patterns of the triangular and square apertures. [4][5][6][7] and diffraction phenomena [8][9][10]. Other applications of light's OAM range from optical manipulation [11] to quantum communication [12,13]. Two recent publications show the importance of this subject applied to optical communications [14] and quantum metrology [15].Particularly interesting is the rich relationship between the phase of light with OAM and diffraction phenomena [9,10,[16][17][18][19][20]. This relationship was well explored by a very simple experiment performed by Hickmann et al.[10]. The basic idea is to observe the Fraunhofer pattern of a diffracted light with OAM by a triangular slit or triangular aperture with the phase singularity aligned on the center of these objects. A truncated triangular optical lattice in the Fraunhofer plane is observed. The size of this optical lattice depends on the amount of OAM, and by counting the number of intensity maxima N of any extern side of the triangular lattice you can obtain the value of TC, m, using a very simple rule, m N − 1. A simple way to understand the formation of this pattern is to observe the diffraction of light with OAM due to each edge of the aperture separately in Fraunhofer plane. Two points must be observed: firstly, the number of fringes due to each edge is proportional to the OAM value, and second, the effect of the azimuthal phase over this diffraction pattern produces a shift proportional to the amount of OAM. By interfering the light diffracted by the three edges, a triangular optical lattice is unveiled. In fact, in [9] the authors showed a detailed study of the diffraction problem of light with OAM by a single slit.They considered two situations where the phase singularity of the light beam strikes on the center of and above a single slit. In the latter case, which is the case for one side of the triangular aperture, the patterns observed are asymmetric and shifted.At this point a very simple question arises: What can we learn about diffracting OAM beam by other polygonal shapes? In [20], results of diffraction of light with OAM by a square aperture were presented. The authors showed numerically and experimentally that a perfect square optical intensity lattice takes place only for even values of the TC.In this Letter, we show a comparative study of the diffraction problem of light with OAM between square and triangular shape. Surprisingly, with a square aperture the value of TC obtai...