L.I. Averina - Dr. Sc. (Phys.-Math.), Associate Professor, Department of Electronics of Faculty of Physics, Voronezh State University E-mail: averina@phys.vsu.ru A.V. Avdeev - Post-graduate Student, Department of Electronics of Faculty of Physics, Voronezh State University E-mail: avdeev@phys.vsu.ru V.A. Stepkin - Ph. D. (Phys.-Math.), Associate Professor, Department of Electronics of Faculty of Physics, Voronezh State University E-mail: stepkin@phys.vsu.ru