1. Physics Department, Aristotle University of Thessaloniki, 54124 Thessaloniki, Greece
2. Institute of High Pressure Physics, Polish Academy of Sciences, Sokołowska 29/37, 01-142 Warsaw, Poland
3. Institute of Physics, Polish Academy of Sciences, Al. Lotników 32/46, 02-668 Warsaw, Poland
4. Institute of Ion Beam Physics and Materials Research, Helmholtz-Zentrum Dresden-Rossendorf, 01328 Dresden, Germany
5. Department of Electrical and Computer Engineering and Center for Photonics Research, Boston University, Boston, Massachusetts 02215, USA