The spatial extent of the wavefront maps 3a, 3b, 3c, 3g, 3h, 3i is 7.91mm x 7.91mm.

Spatial-frequency spectra 3d, 3e, 3f, 3j, 3k, 3l were obtained by taking Fast Fourier Transformation of wavefront images 3a, 3b, 3c, 3g, 3h, 3i correspondingly. 

In the paper, figures 3d, 3e, 3f, 3j, 3k, 3l show only central parts of the calculated spatial-frequency spectra. They were also visually enhanced by removing background noise.
