1. Institute of Geotechnics, SAS, Watsonova 45, 040 01 Košice, Slovakia
2. Institute of Experimental Physics, SAS, Watsonova 47, 040 01 Košice, Slovakia
3. Institute of Material Science of Seville (CSIC-US), 410-92 Seville, Spain
4. Institute of Electronics and Photonics, Slovak University of Technology and International Laser Centre, 812 19 Bratislava, Slovakia