1 HiLASE Centre, Institute of Physics, Czech Academy of Sciences, Za Radnici 828, Dolni Brezany 252 41, Czech Republic
2 National Institute for Fusion Science, National Institutes of Natural Sciences, 322-6, Oroshi-cho, Toki, Gifu 509-5292, Japan
3 Kitami Institute of Technology, 165 Koen-cho, Kitami, Hokkaido, Japan
4 Department of Physical Electronics, Faculty of Nuclear Sciences and Physical Engineering, Czech Technical University in Prague, Brehova 7, Prague 115 19, Czech Republic