The Talbot effect has revived in many fields of modern optics. As a key number of self-imaging, the fundamental Talbot length plays a crucial role in many applications. However, the inspection of the Talbot carpet for determining the Talbot length is only applicable, if the two-dimensional field distribution behind the grating is represented by a one-dimensional cross-section. In this letter, we show an effective way to overcome this limitation to explore the self-imaging of gratings with complex two-dimensional periodicities. For that purpose, the near-field diffraction is analyzed using the Pearson correlation coefficient of the intensity distribution in Fourier space. We report results on linear, ring, and spiral gratings.

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