Frequency-tunable vertical external cavity terahertz quantum cascade laser – TERASEL

Context – THz waves (1-10 THz) are non-ionizing radiation that can potentially find applications in a variety of domains. The most promising at this time are THz imaging and spectroscopy. Quantum cascade lasers (QCL) have emerged as one of the rare compact and powerful THz sources that potentially suit such applications. They can operate at 50/80K with compact Stirling coolers systems or at liquid nitrogen temperature. Beside the available optical power which is an important parameter, what is really limiting the widespread commercial success of THz QCLs is the lack of frequency tunability.

Objectives – The goal of the project TERASEL is to develop a highly tunable THz Quantum Cascade Vertical External Cavity Surface Emitting Laser (QC-VECSEL). It will consist of an active medium made of an electrically pumped semiconductor/metal microstructures, providing a reflective gain thanks to THz intersubband transitions. The laser will be frequency tunable thanks to the use of a frequency-selective adjustable external mirror. We target the 2.5-4.5 THz range, with operating temperatures in the 50-80K range and CW output powers larger than 10 mW.
An additional objective of the project will be to demonstrate a free-space optical amplifier for THz waves which currently does not exist. Such a device would be useful for extending the practical frequency range of TDS systems above 2 THz or for broadband amplification of THz pulses from mode-locked QCLs.

Team – The consortium consists of 3 complementary research groups which are major national and international actors in the domain of QCLs: IES (molecular beam epitaxy of QCLs), C2N (THz photonic microstructure and devices) and LPA (TDS, pulsed QCL, dynamic gain).

Relevance – The concept of THz QC-VECSEL is novel, original and very promising. This idea has been recently shown by a USA research team at UCLA. Our proposal builds on this extremely recent development and aims at contributing to this emerging field with state of the art results thanks to an early start and the mobilization of a complimentary and expert consortium.
The project innovates in at least 3 aspects: first, we aim at demonstrating a practical THz VECSEL with large frequency tunability (10%); second, we aim at improving considerably the output power performance of the tuneable laser compared to the state-of-the-art; third, we plan to use the envisioned devices as amplifiers of THz pulses from TDS systems and MOPA for mode-locked QCLs.
An additional important point is the timeliness of this proposal relative to this emerging hot topic, but also relative to the national structuration of the research in the field. For the first time, the complete fabrication chain (quantum and optical design, growth, characterizations) is available in France, thanks to the state of the art growth of THz QCLs at IES. An important objective of this project is therefore to rapidly capitalize on this situation by demonstrating advances with strong applicative potential.