Research

The terahertz (THz) field lies at the intersection of photonics and electronics. THz waves are characterized by a frequency ranging from 100 GHz to 10 THz, corresponding to the natural vibration frequencies of many molecules; a wavelength ranging from 30 µm to 3 mm, which gives them strong penetrating power; and low energy (0.4 to 4 meV), making them completely harmless, particularly to living organisms. Furthermore, a large number of materials are transparent to THz radiation, also known as T-rays. However, these rays are reflected by metals and absorbed by polar liquids, including water. These specific properties give rise to a wide range of applications for THz spectroscopy and THz imaging in fields as diverse as cosmology, non-destructive testing, security, and heritage studies…

But THz spectroscopy also makes it possible to probe a wide range of fundamental physical phenomena in condensed matter and living matter. Indeed, the energy of THz waves corresponds to that of many elementary excitations, such as plasmons, magnons, phonons, Landau inter-level transitions, and electron spin resonances.

The TOP platform’s activities encompass both fundamental research based on THz spectroscopy techniques and research focused on the development of new sensors and emitters, as well as more applied research that combines THz imaging and spectroscopy with agronomy, for example.

THz research at the Montpellier site began in 1983 with the publication of a theoretical article by M. Dyakonov [1], a professor at the University. In 2002, W. Knap reported the first detection of THz radiation by a nanotransistor [2]. The team, consisting of F. Teppe, N. Dyakonova, D. Coquillat, and W. Knap, subsequently developed this research at the site from 2003 to 2013. Following the filing of several patents related to the development and integration of THz sources and detectors, the startup T-Waves Technologies—which has since become Terakalis—was founded in 2013. Terakalis develops non-destructive testing systems for industrial materials, based on THz imagers derived from the team’s patents.

At the same time, the Institute of Electronics and Systems (IES UMR 5214) launched a program in 2001 [3] to simulate physical phenomena in electronic components in the THz frequency range. The development of an experimental program at the IES, initially led by L. Chusseau and J. Torres, helped bring the two laboratories closer together, notably through the creation of a Scientific Interest Group called “TeraLab” in 2010. With support from the CNRS, the University of Montpellier, and the Occitanie region; and in a spirit of unifying and structuring the regional cluster; the Occitanie Terahertz Platform (Terahertz Occitanie Platform – TOP), at the interface between the L2C and the IES, was created in 2017.

Since 2012, new research activities have been developing within the framework of the TOP platform. In solid-state physics, a magneto-spectroscopy system capable of probing the band structure of topological and Dirac materials was developed by S. Ruffenach and F. Teppe [5]. More recently, a Landau spectroscopy system—unique in Europe and developed in 1993 by W. Knap—was recommissioned by C. Consejo and F. Teppe to study cyclotron emission in Dirac materials [6, 7]. And most recently, a THz magneto-photoconductivity spectroscopy system was developed by C. Bray, C. Consejo, K. Maussang, and F. Teppe [8] to study electronic spin resonances in two-dimensional materials such as graphene. In biophysics, S. Ruffenach, L. Varani, and J. Torres are developing near-field THz spectroscopy systems to study quantum electrodynamic interactions between proteins [9]. Finally, C. Bray, N. Diakonova, and D. Coquillat have developed an imaging system to study plants [10].

All of these tools—transmitters, detectors, and spectrometers—were pooled together when the Terahertz Occitanie Platform (TOP) was established.

[1] M. Dyakonov and M. Shur, Phys. Rev. Lett. 71, 2465 (1993).
[2] W. Knap et al., Appl. Phys. Lett. 81, 4637 (2002).
[3] E. Starikov et al. J. Appl. Phys. 89, 1161 (2001).
[4] V. Gruzinskis et al., Phys. Stat. Sol. (b) 204, 77 (1997).
[5] F. Teppe et al. Nature Communications 7, 12576 (2016).
[6] D. But et al., Nature Photonics 13, 783–787 (2019).
[7] S. Gebert, C. Consejo et al., Nature Photonics 17, 244–249 (2023).
[8] C. Bray, K. Maussang et al., Phys. Rev. B 106, 245141 (2022).
[9] M. Lechelon, et al., Science Adv. 8(7): eabl5855 (2022)
[10] Y. Abautret, et al., OPTICS EXPRESS 28, 35018–35037 (2020).