1. Physics FacultyVilnius University Vilnius 00122 Lithuania
2. Research Institute for Nuclear ProblemsBelarusian State University Minsk 220030 Belarus
3. Department of Characterisation of Materials StructureCenter for Physical Sciences and Technology Vilnius 10257 Lithuania
4. Institute of PhotonicsUniversity of Eastern Finland Yliopistokatu 7 Joensuu FI-80101 Finland