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A. Achim
National Institute R&D for Laser, Plasma and Radiation Physics, Solid-State Quantum Electronics Laboratory, P.O. Box MG 36, 077125 Magurele, Bucharest, Romania
L. Gheorghe
National Institute R&D for Laser, Plasma and Radiation Physics, Solid-State Quantum Electronics Laboratory, P.O. Box MG 36, 077125 Magurele, Bucharest, Romania
F. Voicu
National Institute R&D for Laser, Plasma and Radiation Physics, Solid-State Quantum Electronics Laboratory, P.O. Box MG 36, 077125 Magurele, Bucharest, Romania