1. Physikalisches Institut, Goethe-Universität, Max-von-Laue-Str. 1, 60438 Frankfurt am Main, Germany
2. Institute of Applied Electrodynamics and Telecommunications, Vilnius University, 10257 Vilnius, Lithuania
3. Center for Terahertz Research and Applications (CENTERA), Institute of High Pressure Physics PAS, 01-142 Warsaw, Poland