Abstract-Diffraction-limited ultrabroadband terahertz spectroscopy.

Baillergeau M1, Maussang K1, Nirrengarten T1, Palomo J1, Li LH2, Linfield EH2, Davies AG2, Dhillon S1, Tignon J1, Mangeney J1.

http://www.ncbi.nlm.nih.gov/pubmed/27142959

• 1Laboratoire Pierre Aigrain, Ecole Normale Supérieure, CNRS (UMR 8551), Université P. et M. Curie, Université D. Diderot, 75231 Paris Cedex 05, France.
• 2School of Electronic and Electrical Engineering, University of Leeds, Woodhouse Lane, Leeds LS29JT, UK.

Diffraction is the ultimate limit at which details of objects can be resolved in conventional optical spectroscopy and imaging systems. In the THz spectral range, spectroscopy systems increasingly rely on ultra-broadband radiation (extending over more 5 octaves) making a great challenge to reach resolution limited by diffraction. Here, we propose an original easy-to-implement wavefront manipulation concept to achieve ultrabroadband THz spectroscopy system with diffraction-limited resolution. Applying this concept to a large-area photoconductive emitter, we demonstrate diffraction-limited ultra-broadband spectroscopy system up to 14.5 THz with a dynamic range of 10(3). The strong focusing of ultrabroadband THz radiation provided by our approach is essential for investigating single micrometer-scale objects such as graphene flakes or living cells, and besides for achieving intense ultra-broadband THz electric fields.

Abstract-Diffraction-limited ultrabroadband terahertz spectroscopy

• M. Baillergeau
• , K. Maussang
• , T. Nirrengarten
• , J. Palomo
• , L. H. Li
• , E. H. Linfield
• , A. G. Davies
• , S. Dhillon
• ,J. Tignon
•  & J. Mangeney
• 
  

http://www.nature.com/articles/srep24811

Diffraction is the ultimate limit at which details of objects can be resolved in conventional optical spectroscopy and imaging systems. In the THz spectral range, spectroscopy systems increasingly rely on ultra-broadband radiation (extending over more 5 octaves) making a great challenge to reach resolution limited by diffraction. Here, we propose an original easy-to-implement wavefront manipulation concept to achieve ultrabroadband THz spectroscopy system with diffraction-limited resolution. Applying this concept to a large-area photoconductive emitter, we demonstrate diffraction-limited ultra-broadband spectroscopy system up to 14.5 THz with a dynamic range of 103. The strong focusing of ultrabroadband THz radiation provided by our approach is essential for investigating single micrometer-scale objects such as graphene flakes or living cells, and besides for achieving intense ultra-broadband THz electric fields. 

Figure 1: THz radiation properties under plane wave-front optical excitation of the emitter at selected frequencies higher than c/(2πwTHz).

Abstract-Room temperature broadband coherent terahertz emission induced by dynamical photon drag in graphene

J. Maysonnave, S. Huppert, F. Wang, S. Maero, C. Berger, W. de Heer, T.B. Norris, L.A. De Vaulchier, S. Dhillon, J. Tignon, R. Ferreira, J. Mangene

http://arxiv.org/abs/1405.6361

Nonlinear couplings between photons and electrons in new materials give rise to a wealth of interesting nonlinear phenomena. This includes frequency mixing, optical rectification or nonlinear current generation, which are of particular interest for generating radiation in spectral regions that are difficult to access, such as the terahertz gap. Owing to its specific linear dispersion and high electron mobility at room temperature, graphene is particularly attractive for realizing strong nonlinear effects. However, since graphene is a centrosymmetric material, second-order nonlinearities a priori cancel, which imposes to rely on less attractive third-order nonlinearities. It was nevertheless recently demonstrated that dc-second-order nonlinear currents as well as ultrafast ac-currents can be generated in graphene under optical excitation. The asymmetry is introduced by the excitation at oblique incidence, resulting in the transfer of photon momentum to the electron system, known as the photon drag effect. Here, we show broadband coherent terahertz emission, ranging from about 0.1-4 THz, in epitaxial graphene under femtosecond optical excitation, induced by a dynamical photon drag current. We demonstrate that, in contrast to most optical processes in graphene, the next-nearest-neighbor couplings as well as the distinct electron-hole dynamics are of paramount importance in this effect. Our results indicate that dynamical photon drag effect can provide emission up to 60 THz opening new routes for the generation of ultra-broadband terahertz pulses at room temperature.

Abstract-Terahertz Radiation from Magnetic Excitations in Diluted Magnetic Semiconductors

R. Rungsawang¹, F. Perez^2,*, D. Oustinov¹, J. Gómez^2,†, V. Kolkovsky³, G. Karczewski³, T. Wojtowicz³, J. Madéo¹,N. Jukam¹, S. Dhillon¹, and J. Tignon^1 
1Laboratoire Pierre Aigrain, Ecole Normale Supérieure, CNRS (UMR 8551), Université Pierre et Marie Curie, Université D. Diderot, 75231 Paris Cedex 05, France
²Institut des Nanosciences de Paris, CNRS (UMR7588), Université Paris VI, Paris 75005, France
³Institute of Physics, Polish Academy of Sciences, 02-668 Warsaw, Poland


http://prl.aps.org/abstract/PRL/v110/i17/e177203

We probed, in the time domain, the THz electromagnetic radiation originating from spins in CdMnTe diluted magnetic semiconductor quantum wells containing high-mobility electron gas. Taking advantage of the efficient Raman generation process, the spin precession was induced by low power near-infrared pulses. We provide a full theoretical first-principles description of spin-wave generation, spin precession, and of emission of THz radiation. Our results open new perspectives for improved control of the direct coupling between spin and an electromagnetic field, e.g., by using semiconductor technology to insert the THz sources in cavities or pillars.

© 2013 American Physical Society

Abstract-Terahertz radiation from magnetic excitations in diluted magnetic semiconductors

R. Rungsawang, F. Perez, D. Oustinov, J. Gómez, V. Kolkovsky, G. Karczewski, T. Wojtowicz, J. Madéo, N. Jukam, S. Dhillon, and J. Tignon
http://prl.aps.org/accepted/c1072Y88G3019b3ce3be8a80c1ecd8d7ec5bd5683
We probed in the time domain, the THz electromagnetic radiation originating from spins in CdMnTe diluted magnetic semiconductors quantum wells containing high mobility electron gas. Taking advantage of the efficient Raman generation process, the spin precession was induced by low power near-infrared pulses. We provide a full theoretical first-principles description of spin-waves generation, spin precession and of emission of the THz radiation. Our results open new perspectives for improved control of the direct coupling between spins and electromagnetic field, e.g. by using semiconductor technology to insert the THz sources in cavities or pillars.