1. Saratov State University, 83 Astrakhanskaya Str., Saratov 410012, Russia
2. SPE Nanostructured Glass Technology, 101, 50 let Oktjabrja ave., Saratov 410033, Russia
3. Institute of Precise Mechanics and Control RAS, 24, Rabochaya Str., Saratov 410028, Russia
4. University of Oulu, P. O. Box 4500, Oulu FIN-90014, Finland