Links
[1] https://www.hootsgo.org/?q=node/6406
[2] http://www.math.ubc.ca/~cass/courses/m309-03a/m309-projects/krzak/
[3] http://en.wikipedia.org/wiki/Diffraction
[4] http://buphy.bu.edu/ulab/intro2/diffraction.pdf
[5] http://m.everythingscience.co.za/grade-11/06-2d-and-3d-wavefronts/06-2d-and-3d-wavefronts-05.cnxmlplus