Dark zone in the centre of the Arago-Poisson diffraction spot of a helical laser beam O. Emile, A. Voisin, R. Niemiec, B. Viaris de Lesegno, L. Pruvost, G. Ropars, J. Emile and C. Brousseau EPL, 101 5 (2013) 54005 Published online: 20 March 2013 DOI: 10.1209/0295-5075/101/54005