1. Department of Physics, “Gheorghe Asachi” Technical University, Iasi 700050, Romania
2. “Petru Poni” Institute of Macromolecular Chemistry, 41 A Gr. Ghica Voda Alley, Iasi 700487, Romania
3. Univ. Lille, CNRS, UMR 8523, PhLAM—Physique des Lasers, Atomes et Molécules, F-59000 Lille, France