[1] Univ Minho, Dept Phys, P-4710057 Braga, Portugal
[2] Univ Minho, Ctr Phys, P-4710057 Braga, Portugal
[3] Univ Fed Rio de Janeiro, Inst Fis, BR-21941972 Rio De Janeiro, RJ, Brazil
[4] Univ Southampton, Optoelect Res Ctr, Southampton SO17 1BJ, Hants, England
[5] Univ Southampton, Ctr Photon Metamat, Southampton SO17 1BJ, Hants, England