Highly tuneable, high power, efficient terahertz source based on dual-frequency-synchronous Tm-doped fibre-laser source – TERATUNE

The terahertz frequency domain (0.1 – 10 THz) is enjoying great interest justified by the unique properties of these electromagnetic waves, enabling many new applications in the security sector, biology, medicine, and communication. Indeed, THz fields interact with many molecules, which results in readily identifiable absorption peaks. They are weakly absorbed by non-metallic and non-polarizing materials (such as textiles, ceramics, plastics and semiconductors, etc.), which makes these materials transparent while they are opaque in the visible range. Besides, THz radiations are non-ionizing making their use safe for biological and medical environments. All these remarkable properties make THz spectroscopy and THz multi-spectral imaging very promising and powerful techniques for analyzing substances, materials, devices and products.
Even if few commercial systems are now available, large efforts in THz source developments are still required for fully exploiting the properties of THz waves in daily applications. Regardless of a great variety of techniques for generating THz radiation, none of them provides a THz source which is simultaneously compact, highly efficient (large output power), broadly tunable, and works at room temperature. THz sources based on difference frequency generation by nonlinear optical effects are very appealing because this technique allows the coverage of the whole THz spectral domain, is power scalable, and can capitalize on swift progress of diode-pumped lasers, especially fiber lasers, which would allow making high power and compact THz sources. However, even if the emerging THz sources based on fiber laser technology demonstrate high performances, compactness, robustness, and simple construction, they are facing the lack of frequency tunability essential for THz spectroscopy and multi-spectral imaging applications.

In the ambitious project TERATUNE, we aim to tackle this bottleneck by exploiting a novel laser architecture developed by IPHT and XLIM’s expertise in novel resonator architectures as well as in specialty active fibers for high power fiber lasers and amplifiers. IPHT has recently developed a novel tuning concept for (nanosecond) pulsed fiber lasers that enables the broadest wavelength tunability (74 nm in the Ytterbium band) with very fast tuning operation in the millisecond range. This novel tuning principle can be further enhanced by an innovative operation mode emitting multiple synchronized pulses with freely adjustable peak wavelengths respectively, offering the unique possibility for generating pulsed THz radiations with frequency tunability. On the other hand, XLIM has recently proposed a novel concept of Very Large Mode Area (VLMA) active fibers that exhibit unique confinement properties for high power single transverse mode amplifiers/lasers. The VLMA fiber unique properties are of great interest to fight off nonlinear drawbacks in the fiber and provide unprecedented peak-power level and suitable spectral and spatial properties for the efficient generation of high power THz radiations with a nonlinear crystal.
TERATUNE aims to exploit these novel technologies for developing the first frequency tunable THz source based on fiber laser technology. The project targets two classes of efficient high-power THz sources: (i) continuously tunable over the frequency range 0.3 – 1 THz for offering an efficient THz source adapted to most THz applications, (ii) ultra-broad band tunability (not continuously) over the THz spectral range for allowing an easier access to the whole THz domain. The success of this ambitious project demands a high-level of scientific expertise in, photonic technology, specialty laser architecture and novel fibers for ultra-high power optical amplifier systems. These skills come together in the collaboration of IPHT and XLIM with complementary competences, providing a stimulating collaborative research environment for students and researchers from both countries.