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, “Gheorghe Asachi” Technical University, 59A Mangeron Blvd., 700050 Iasi, Romania
3. Department of Physics, Alexandru Ioan Cuza University, 11 Carol I Blvd., 700506 Iasi, Romania