Propagation of optical beams in two transverse gradient index mediaA. Martín-Ruiz, J. Martín-Heredia, L. A. Ruiz-Ochoa and E. Chan-LópezEur. Phys. J. D, 70 5 (2016) 110DOI: https://doi.org/10.1140/epjd/e2016-60645-4