Fiber & Waveguide Lasers
Prof. Dr. Jens LIMPERT
Fiber lasers lab.
Image: Tobias Tieß and Charles Loussert
Prof. Dr. Jens Limpert
Image: PrivateProf. Dr. Jens LIMPERT
Email: jens.limpert@uni-jena.de
Phone: +49 3641-9-47811
Prof. Jens Limpert heads the Fiber & Waveguide Lasers Group at the Institute of Applied Physics of Friedrich Schiller University Jena. He is also affiliated with the Helmholtz Institute Jena and the Fraunhofer Institute for Applied Optics and Precision Engineering IOF.
His research focuses on the development of high-performance fiber and waveguide laser systems, with particular emphasis on scaling ultrafast lasers to extreme average powers and pulse energies while maintaining excellent beam quality. Central research directions include coherent beam combining, multicore and large-mode-area fibers, high-power lasers around 1 µm and 2 µm, few-cycle pulse generation, and fiber-laser-driven secondary photon sources extending into the extreme-ultraviolet spectral range.
Research Areas
Prof. Limpert's research focuses on power and energy scaling of fiber-based laser systems and on the development of novel photonic architectures that overcome the thermal and nonlinear limitations of individual laser channels. Research interests include:
- High-power and high-energy ultrafast fiber lasers
- Coherent beam combining of multiple laser amplifiers
- Multicore and large-mode-area active fibers
- Novel fiber and waveguide designs for power scaling
- Transverse mode instabilities and nonlinear limitations in high-power fibers
- High-power thulium-doped fiber lasers in the 2 µm wavelength range
- Few-cycle and carrier-envelope-phase-stable laser systems
- Nonlinear pulse compression and temporal pulse shaping
- High-order harmonic generation and coherent EUV sources
- High-average-power drivers for attosecond science, imaging and strong-field applications
Teaching Fields
Prof. Limpert teaches courses in the fundamentals of laser physics both for the M.Sc. Photonics and for the M.Sc. Physics, including:
- Fundamentals of laser physics
- Fiber and waveguide lasers
- High-power laser physics
- Ultrashort-pulse laser technology
- Nonlinear optics
Research Methods
The group develops advanced fiber and waveguide laser architectures and combines laser-system engineering with detailed spatial, temporal and spectral characterization. Methods include:
- Design and fabrication of large-mode-area and multicore active fibers
- Chirped-pulse amplification in fiber-based laser systems
- Coherent spatial and temporal beam combining
- Active and passive phase stabilization of multi-channel laser systems
- High-power pump architectures and thermal-management concepts
- Nonlinear pulse compression and few-cycle pulse generation
- Carrier-envelope-phase stabilization
- Spatial and temporal pulse shaping
- Beam-quality, wavefront and modal-content characterization
- Measurement and mitigation of transverse mode instabilities
- Fiber-based nonlinear frequency conversion
- High-order harmonic generation driven by high-average-power fiber lasers
Recent Research Results
Coherent beam combining has become a central strategy for scaling ultrafast fiber lasers beyond the limitations of individual amplifier channels. By distributing amplification across multiple parallel fibers and coherently recombining their outputs, high pulse energy and high average power can be achieved simultaneously. A coherently combined system based on 16 ytterbium-doped fiber amplifiers demonstrated 1 kW average power, 10 mJ pulse energy and 120 fs pulse duration while maintaining near-diffraction-limited beam quality [1].
Current research extends this concept towards multicore active fibers, in which several amplifier channels are integrated into a single fiber structure. In 2026, a 3 × 3 ytterbium-doped multicore fiber amplifier reached 3.2 kW total output power with excellent stability and a slope efficiency exceeding 86%, demonstrating the potential of core-count scaling for future multi-kilowatt fiber laser architectures [2].
A second major research direction is the development of high-power fiber lasers around 2 µm. Thulium-doped silica provides favourable scaling of thermal and nonlinear effects and enables access to a wavelength range attractive for nonlinear optics, strong-field physics and secondary-source generation. Using in-band pumping, recent systems have reached 9 mJ pulse energy at 540 W average power and up to 1.4 kW in continuous-wave operation from a single fiber channel [3].
The group also investigates the generation of extremely short pulses at high average power. Fiber-based systems combined with nonlinear post-compression have recently enabled carrier-envelope-phase-stable, sub-two-cycle pulses with more than 400 W average power [4].
High-performance fiber lasers furthermore serve as drivers for nonlinear frequency conversion and high-order harmonic generation. Together with the X-ray Spectroscopy and Microscopy group, coherently combined femtosecond fiber lasers have enabled compact coherent EUV sources with exceptionally high photon flux and nanoscale lensless imaging, establishing a direct link between fiber-laser power scaling and advanced short-wavelength photonics [5].
[1] Stark et al., Opt. Lett. 46, 969 (2021).
[2] Khalil et al., Opt. Lett. 51, 1677 (2026).
[3] Lenski et al., Opt. Express 34, 35811 (2026).
[4] Seres et al., High Power Laser Sci. Eng. 14, e11 (2026).
[5] Lenski et al., Opt. Lett. 49, 4042 (2024).