Highly tunable, high power, efficient terahertz source based on dual-frequency synchronous Thulium-doped fiber laser source

• Applicant: Dr. Matthias Jäger, Ph.D.
• Subject Area: Optics, Quantum Optics and Physics of Atoms, Molecules and Plasmas
• Term: from 2015 to 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 283997287

Terahertz radiation (0.1 - 10 THz) has attracted great interest due to its unique properties, enabling many new applications in the security sector, biology, medicine, and in communications. While THz radiation is weakly absorbed by non-metallic non-polarizing materials, it acts non-ionizing on biological tissue and interacts with many molecules, resulting in readily identifiable absorption peaks. These remarkable properties make THz spectroscopy and multi-spectral imaging very promising and powerful techniques for analyzing substances, materials, devices and products.Even if first commercial systems emerge, large efforts in THz source developments are still required for fully exploiting the properties of THz waves in daily applications. So far, none of numerous THz generation techniques provides a source, which is simultaneously compact, highly efficient (high power), broadly tunable, and works at room temperature. THz sources based on difference frequency generation (DFG) in a nonlinear crystal pumped by diode pumped fiber laser systems are highly attractive since they combine power scalability with the inherent advantages of fiber-integrated setups. However this powerful approach has not been merged yet with frequency tunability essential for THz spectroscopy and multi-spectral imaging applications.This ambitious project aims to tackle this bottleneck by exploiting a novel fiber laser architecture developed by IPHTs and XLIMs expertise in innovative designs for high-power fiber lasers and amplifiers. Using a configurable fiber Bragg grating array with tailored tuning characteristics, the IPHT has recently demonstrated a record tuning bandwidth (74nm in the Yb band) in an electronically tunable nanosecond fiber laser. In a novel resonator design, the IPHT has enhanced this principle towards spectrally independent pulse round trip times enabling a unique dual-frequency operation regime. For the first time, a single fiber-integrated resonator enables a synchronous emission of 2 pulses with tunable emission wavelengths. Together with novel Very Large Mode Area active fibers developed by XLIM, exhibiting unique confinement properties for high power single transverse mode amplifiers while suppressing nonlinear distortions in the system, these techniques enable a pulsed broadly tunable high-power THz source using DFG in a nonlinear crystal.TERATUNE aims to exploit this concept based on a Tm-doped fiber laser and amplifier scheme for developing two classes of high-power THz sources: (i) continuously tunable over the frequency range 0.3 - 1 THz adapted to most THz applications, (ii) discretely tunable covering almost the entire THz regime. 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.

• DFG Programme: Research Grants
• International Connection: France
• Partner Organisation: Agence Nationale de la Recherche / The French National Research Agency
• Cooperation Partners: Dr. Georges Humbert; Dr. Philippe Roy