Recent results obtained in the terahertz frequency range on flat or corrugated structures combining plasmonic waveguides and resonators will be presented. Plasmonics are useful for many applications at different frequencies from Terahertz to infrared and to the visible range. In this communication I will focus on applications at terahertz frequencies  following these three parts :
-Terahertz Quantum Cascade Lasers (QCL) beam-shaping
-Terahertz Arrays : Split Ring Resonators
For the THZ-QCLs, a very promising approach has been proposed by Prof. F Capasso (Harvard University). It is based on plasmonic effects and constructive interferences for lattices at one facet of the QCL. All of these different approaches have quite similar main-lobe beamwidths at THz frequencies. The challenge is now to reduce even more this beamwidth with original approaches. We are developing bull-eye arrays for THz QCL in collaboration with the Public University of Navarra. The shape of the first corrugations plays an important role in order to reach ultra-directive radiations. Plasmonic arrays for the beamshaping of terahertz sources inserted in waveguides or from terahertz quantum cascade lasers (THz-QCL) will be both presented. In a second part, I will also present recent advances in the field of metamaterials at Terahertz frequencies with high refractive indexes for example. I will focus on the different ways to excite resonators from free space propagating waves and also from guided waves with a Planar Goubau Line (PGL) . This work is done in collaboration with Prof. W. Padilla (Boston College). Several schemes of excitations will be described from simulations and measurements results up to 0.5THz. In the last part, I will present an original topology for THz microscopy based on PGL.
 All the articles published in the Focus Issue of the New Journal of Physics Focus on Terahertz Plasmonics.
 W.- C. Chen, J. J. Mock, D. R. Smith, T. Akalin and W. Padilla, "Controlling gigahertz and terahertz surface electromagnetic waves with metamaterial resonators", Physical Review Express, Vol.1, Issue 2, PRX-2011.