*Elena Zharkikh1,2, Evgeny Zherebtsov1,2, Igor Kozlov2, Angelina Zherebtsova2, Viktor Dremin2, Andrey Dunaev2, Igor Meglinski1
(1. Opto-Electronics and Measurement Techniques Research Unit, University of Oulu, Oulu, Finland, 2. Orel State University named after I.S. Turgenev, 95 Komsomolskaya St., Orel, 302026, Russia)