M.V. Koltsov - postgraduate student of Department of Physics and Optical System Technique, Nizhny Novgorod State Technical University n.a. R.E. Alekseev. E-mail: tirinox@gmail.com S.B. Raevsky - Dr.Sc. (Eng.), Professor of Department of Physics and Optical System Technique, Nizhny Novgorod State Technical University n.a. R.E. Alekseev. E-mail: raevsky@nntu.nnov.ru