S.V. Kiyashko − Dr.Sc. (Phys.-Math.), Senior Research Scientist, Institute of Applied Physics of Russian Academy of Science, Nizhny Novgorod, Russia. E-mail: kiyashko@appl.sci-nnov.ru
V.O. Afenchenko − Ph.D. (Phys.-Math.), Institute of Applied Physics of Russian Academy of Science, Nizhny Novgorod, Russia. E-mail: afen@appl.sci-nnov.ru
A.V. Nazarovsky − Ph.D. (Phys.-Math.), Institute of Applied Physics of Russian Academy of Science, Nizhny Novgorod, Russia. E-mail: nazarovsky@appl.sci-nnov.ru