Abstract-Cavity-based photoconductive sources for real-time terahertz imaging

J. Hawecker, V. Pistore, A. Minasyan, K. Maussang, J. Palomo, I. Sagnes, J.-M. Manceau, R. Colombelli, J. Tignon, J. Mangeney, and S. S. Dhillon

(a) Optical image (front) of the object. (b) Optical image (back of object) of hidden text. (c) Real-time image from the THz camera using the high average power from the quasi-cavity PC switch showing the hidden text. 

https://www.osapublishing.org/prj/abstract.cfm?uri=prj-8-6-858

Optically driven photoconductive switches are one of the predominant sources currently used in terahertz imaging systems. However, owing to their low average powers, only raster-based images can be taken, resulting in slow acquisition. In this work, we show that by placing a photoconductive switch within a cavity, we are able to generate absolute average THz powers of 181 μW with the frequency of the THz emission centered at 1.5 THz—specifications ideally adapted to applications such as non-destructive imaging. The cavity is based on a metal–insulator–metal structure that permits an enhancement of the average power by almost 1 order of magnitude compared to a standard structure, while conserving a broadband spectral response. We demonstrate proof-of-principle real-time imaging using this source, with the broadband spectrum permitting to eliminate strong diffraction artifacts.

© 2020 Chinese Laser Press

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-Engineered far-fields of metal-metal terahertz quantum cascade lasers with integrated planar horn structures

F. Wang, I. Kundu, L. Chen, L. Li, E. H. Linfield, A. G. Davies, S. Moumdji, R. Colombelli, J. Mangeney, J. Tignon, and S. S. Dhillon

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-24-3-2174

The far-field emission profile of terahertz quantum cascade lasers (QCLs) in metal-metal waveguides is controlled in directionality and form through planar horn-type shape structures, whilst conserving a broad spectral response. The structures produce a gradual change in the high modal confinement of the waveguides and permit an improved far-field emission profile and resulting in a four-fold increase in the emitted output power. The two-dimensional far-field patterns are measured at 77 K and are agreement in with 3D modal simulations. The influence of parasitic high-order transverse modes is shown to be controlled by engineering the horn structure (ridge and horn widths), allowing only the fundamental mode to be coupled out.

© 2016 Optical Society of America

Full Article  |  PDF Article

Abstact-Terahertz emission from multiple-microcavity exciton-polariton lasers

S. Huppert, O. Lafont, E. Baudin, J. Tignon, and R. Ferreira

https://journals.aps.org/prb/abstract/10.1103/PhysRevB.90.241302

Terahertz emission between exciton-polariton branches in semiconductor microcavities is expected to be strongly stimulated in the polariton laser regime due to the high density of particles in the lower state (final-state stimulation effect). However, nonradiative scattering processes depopulate the upper state and greatly hinder the efficiency of such terahertz sources. In this work, we suggest a scheme using multiple microcavities and exploiting the transition between two interband polariton branches located below the exciton level. We compare the nonradiative processes loss rates in single and double cavity devices and we show that a dramatic reduction can be achieved in the latter, enhancing the efficiency of the terahertz emission.

DOI: http://dx.doi.org/10.1103/PhysRevB.90.241302

• 
• 
• 

• Published 8 December 2014
• Received 9 September 2014
• Revised 6 November 2014

©2014 American Physical Society

Abstract-20 THz broadband generation using semi-insulating GaAs interdigitated photoconductive antennas

P. J. Hale, J. Madeo, C. Chin, S. S. Dhillon, J. Mangeney, J. Tignon, and K. M. Dani  »View Author Affiliations

http://www.opticsinfobase.org/oe/abstract.cfm?uri=oe-22-21-26358

Optics Express, Vol. 22, Issue 21, pp. 26358-26364 (2014)
http://dx.doi.org/10.1364/OE.22.026358

We demonstrate broadband (20 THz), high electric field, terahertz generation using large area interdigitated antennas fabricated on semi-insulating GaAs. The bandwidth is characterized as a function of incident pulse duration (15-35 fs) and pump energy (2-30 nJ). Broadband spectroscopy of PTFE is shown. Numerical Drude-Lorentz simulations of the generated THz pulses are performed as a function of the excitation pulse duration, showing good agreement with the experimental data.

© 2014 Optical Society of America

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.