At the fiber and waveguide lasers group we are constantly striving for further developments in laser technology and, in particular, in fiber lasers. From all the laser concepts, fiber lasers are the one which has experienced the most dramatic development in the last decade. Fiber lasers have evolved from laboratory curiosities to full-fledged high-power systems with a deep penetration in both scientific and industrial applications. Jens Limpert leads the Laser Development Group at the Institute of Applied Physics. Furthermore, he is a scientific member of the Helmholtz Institute Jena and a member of the directorate of the Fraunhofer Institute for Applied Optics and Precision Engineering, Jena.
In his research, Prof. Limpert investigates novel laser source concepts. Research thrusts include:
Prof. Limpert teaches courses in the fundamentals of laser physics both for the M.Sc. Photonics and for the M.Sc. Physics.
The laboratories run by Prof. Limpert offer a wide range of complex setups and characterization methods to establish and study novel optical components:
The Fiber and Waveguide Laser Group has demonstrated a significant performance scaling of fiber-based laser systems in recent years. Based on a fundamental knowledge of waveguide optics and laser physics, novel fiber designs such as the rod-type large pitch photonic crystal fiber have been invented. This fiber design is based on a novel mechanism, the delocalization of higher order transverse modes, and allows for single-mode extraction from a core size of ytterbium-doped fibers as large as 135 µm, 135 times larger than the guided wavelengths. This record mode area has enabled an enormous performance increase in ultrafast fiber laser systems. Gigawatt peak power, in combination with several 100 W of average power, constitutes unique laser parameters [1, 2].
To extract a performance which is beyond the capabilities of a single aperture emission, the approaches of spatially separated amplification, followed by the coherent addition of amplified femtosecond pulses, are pursued. These concepts are based on the idea of distributing the load or challenges, respectively, to more than just one amplifier channel. In this regard, an amplifying interferometer is constructed. Besides producing a careful numerical analysis, the group has been able to extract parameters beyond the capabilities of a single channel emission , demonstrating a new and promising scaling concept for ultrafast lasers. Based on this work, fiber based laser systems are now considered potential drivers for laser wake-field particle accelerators. Besides performance scaling fundamental effect in amplifying fibers are investigated. Among them thermally induced modal instabilities. This new affect is a serious issue for high average power fiber laser system. Over the recent years the group has contributed to the understanding of that effect and proposed most efficient mitigation strategies .
Transferring the performance of high-repetition rate fiber lasers to new wavelength regions would enable a number of novel applications. We have revealed an unprecedented potential of Thulium-doped fiber lasers most recently. The favorable scaling when shifting the emission wavelength to 2 µm of mode area and nonlinear effects are the basis for a push in obtainable peak power, whereas the higher thermal robustness of long-wavelength fiber lasers hold the promise for high average powers. In addition, the provided gain bandwidth of thuliumdoped silica would support pulses as short as 60 fs. In terms of optical cycles that would correspond to a 25 fs emission at 800 nm. The group has demonstrated multi-GW peak power and kW average power ultrafast thulium-based fiber laser systems [5,6]. Therefore, 2 µm fiber lasers might be considered as the long-wavelength counterpart of Titanium:Sapphire lasers in the future, but in an average-power scalable platform, which is most beneficial for an inexhaustible number of applications.
 Stutzki et al., Optica Vol. 1, 233 (2014).
 Limpert et al., Light: Science & Applications 1 (e8), 1 (2012).
 Klenke et al., Opt. Lett. 39, 6875 (2014).
 Jauregui et al., Nature Photon. 7, 861 (2013).
 Gaida et al., Opt. Lett. 41, 4130 (2016).
 Gaida et al., Opt. Lett. 43, 5853 (2018).
 Müller et al., OpT. Lett. 43, 3083 (2020).