1. Laboratoire de Physique des Lasers, Atomes et Molécules (UMR 8523), Université des Sciences et Technologies de Lille, Villeneuve d’Ascq cedex 59655, France
2. Department of Physics, “Gh. Asachi” Technical University, 59A Mangeron Blvd., 700050 Iasi, Romania
3. Department of Physics, “Alexandru Ioan Cuza” University, 11 Carol I Blvd., 700506 Iasi, Romania