Ray optics hamiltonian approach to relativistic self focusing of ultraintense lasers in underdense plasmasAlessandro Curcio, Maria Pia Anania, Fabrizio Giuseppe Bisesto, Massimo Ferrario, Francesco Filippi, Danilo Giulietti and Massimo PetrarcaEPJ Web of Conferences, 167 (2018) 01003DOI: https://doi.org/10.1051/epjconf/201816701003