Dark zone in the centre of the Arago-Poisson diffraction spot of a helical laser beamO. Emile, A. Voisin, R. Niemiec, B. Viaris de Lesegno, L. Pruvost, G. Ropars, J. Emile and C. BrousseauEPL, 101 5 (2013) 54005DOI: https://doi.org/10.1209/0295-5075/101/54005
