Highly tunable, high power, efficient terahertz source based on dual-frequency synchronous Thulium-doped fiber laser source
Final Report Abstract
Terahertz radiation and THz sources are currently a ‘hot’ research topic due to their unique properties that are enabling new applications in the security sector, biology, medicine, and communications. Besides applications relying on the transparency of many materials in the THz region, THz spectroscopy and multispectral imaging are very powerful techniques for analyzing substances, materials, and devices. One of the required key components for these approaches are a tunable THz sources. The goal of this TERATUNE project as a DFG-ANR collaboration of the Leibniz Institute of Photonic Technology (IPHT) and the XLIM institute of the University of Limoges (France) is the research towards such a tunable THz source. The proposed route is Difference Frequency Generation (DFG) in a nonlinear crystal, which requires in turn a special laser system offering tunable dual-wavelength emission with very high peak power. The research towards such a novel laser source is based on a proposal of the IPHT, which was filed for a patent prior to this project and has meanwhile been granted. A further work package of the Leibniz IPHT involves the investigation of a preamplifier with very large spectral coverage and the joint work towards further power scaling and investigation of alternative laser sources. While all of the IPHT goals have been achieved during the course of the project, the THz work is still ongoing at the XLIM institute. The proposed and demonstrated all-fiber-integrated laser source is very unique in its performance, because the wavelength tuning is accomplished without any moving parts and is entirely based on an electronic signal applied to a acousto-optic modulator. Therefore, it also inherits all other advantages of fiber lasers like compactness, efficiency, robustness, beam quality, etc. The laser resonator has been initially investigated in the single-wavelength mode with a focus on the spectral coverage offered a tunability of 109 nm. But the tuning concept proposed by the IPHT allows even the generation of two (or more) synchronized and independently tunable wavelengths, which is essential for THz generation via difference frequency generation. Dual-frequency generation was eventually achieved with the same wide spectral coverage. By incorporating a temperature-based fine tuning of the fiber gratings, the IPHT could demonstrate a continuous tuning of the frequency difference 0.16 to 6.00 THz. The preamplifier (work package 2) is by comparison more straightforward in terms of the power scaling concept, but the challenge is to maintain the wide spectral coverage and match it to the seed laser. By thorough characterization and careful design, the dual wavelength emission could be amplified with the spectral coverage exceeding 100 nm. In joint experiments in Limoges (work package 3), the peak power in the pulses could be demonstrated up to 10 kW, despite the onset of undesired nonlinear optical effects in the fiber (e.g. spectral broadening and four wave mixing). The THz generation in nonlinear crystals (work package 4) has not been successful yet, but the experiments will be continued at the XLIM institute. In conclusion, the stimulating and collaborative research environment within TERATUNE lead to a vast progress in the field of tunable Thulium-doped fiber-based MOPA systems, uniquely enabling synchronized dual-wavelength emission at peak powers approaching 10kW. Additionally, these dual emission laser sources present real qualities for further fields of applications, such as differential absorption LIDARS (DIAL) for the detection of pollutants for example or the precise measurement of composition of the atmosphere. Another important application of tunable fiber lasers in the 2µm wavelength region is the laser material processing of plastics. Prior to the Teratune project, the IPHT has successfully applied for a patent on the theta cavity in early 2015, which was granted in Mai 2018. Based on this patent and the Teratune results, the IPHT has jointly applied for the industry-led BMBF-funded project “PolyLas”. The goal of this “KMU Innovativ” project is the investigation of polymer welding processes using a novel fiber laser with adjustable wavelength and pulse duration as newly selectable process parameters. The projects partners are five small and medium enterprises (SME) from Germany.
Publications
- “Dual-Wavelength fiber laser based on a theta ring cavity and an FBG array with tailored tuning range for THz generation,” Laser Congress (OSA) Advanced Solid State Lasers (ASSL), Nagoya (2017)
T. Tiess, M. Sabra, M. Becker, M. Rothhardt, G. Humbert, P. Roy, H. Bartelt, M. Jäger
(See online at https://doi.org/10.1364/ASSL.2017.JM5A.35) - “Tunable fiber lasers based on fiber Bragg grating arrays – a powerful platform for spectral and temporal pulse control and multi-wavelength emission,” 5th Workshop Specialty Optical Fibers and Their Applications WSOF, Limassol/Cyprus (2017)
T. Tiess, A. Hartung, M. Becker, M. Rothhardt, H. Bartelt, M. Jäger
- “Tunable all-fiber PM lasers with single-and dual-wavelength emission and extended tuning range at 1µm and 2µm,” Presentation at the Advanced Photonics Congress (OSA) – Specialty Optical Fibers Conference, Zurich (2018)
T. Tiess, M. Becker, M. Rothhardt, Hartmut Bartelt, M. Jäger
(See online at https://doi.org/10.1364/SOF.2018.SoTh2H.4) - “Flexible tuning concept for fiber-integrated lasers featuring multi-wavelength emission with fast switching speeds for DIAL”, Proc. SPIE 11127, Earth Observing Systems XXIV, 111272D (2019)
T. Tiess, M. Becker, M. Rothhardt, Hartmut Bartelt, M. Jäger
(See online at https://doi.org/10.1117/12.2529150) - “Widely Tunable Dual-Wavelength Fiber Laser in the 2 μm Wavelength Range” J. of Lightwave Technol. 37, 2307-2310 (2019)
M. Sabra, B. Leconte, D. Darwich, R. Dauliat, T. Tiess, R. Jamier, G. Humbert, M. Jäger, K. Schuster and P. Roy
(See online at https://doi.org/10.1109/JLT.2019.2902076) - “Widely tunable Q-switched dual-wavelength synchronous-pulsed Tmdoped fiber laser emitting in the 2 μm region,” Opt. Lett. 44, 4690-4693 (2019)
M. Sabra, B. Leconte, R. Dauliat, D. Darwich, T. Tiess, A. Schwuchow, R. Jamier, G. Humbert, K. Wondraczek, M. Jäger, and P. Roy
(See online at https://doi.org/10.1364/OL.44.004690) - “Tunable fiber laser concepts in the 2µm spectral range for tunable dual wavelength emission,” Proc. SPIE 11357, Fiber Lasers and Glass Photonics: Materials through Applications II, 1135741 (2020)
T. Tiess, A. Hartung, M. Becker, M. Rothhardt, R. Dauliat, B. Leconte, G. Humbert, P. Roy, M. Jäger
(See online at https://doi.org/10.1117/12.2559948)
