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- ItemA stimulated Stokes Raman scattering-based approach for continuous wave supercontinuum generation in optical fibers(Philadelphia, Pa. : IOP Publ., 2019) Arshad, Muhammad Assad; Hartung, Alexander; Jäger, MatthiasWe report on a new and simple approach for continuous wave supercontinuum generation in optical fibers. Our new approach uses the effect of stimulated Stokes Raman scattering in a low loss fiber ring laser. By continuously pumping this ring laser with up to 19 W optical power we excited up to six Stokes orders and covered a wavelength range of 500 nm. Due to the feedback mechanism of the ring layout additional nonlinear effects occurred next to the plain generation of individual Stokes peaks. Eventually, these effects broaden and merge the separated Stokes peaks and create a single, connected continuous supercontinuum. By using the effect of stimulated Stokes Raman scattering, we do not rely on anomalous dispersion and modulation instability as typically required for continuous wave supercontinuum generation. © 2019 Astro Ltd.
- ItemIntra-cavity measurement concept of dispersion properties with a tunable fiber-integrated laser(Philadelphia, Pa. : IOP Publ., 2019) Tiess, Tobias; Hartung, Alexander; Becker, Martin; Chojetzki, Christoph; Rothhardt, Manfred; Bartelt, Hartmut; Jäger, MatthiasThe dispersion properties of fibers depict a key characteristic to model the propagation of ultra-short pulses in waveguides. In the following, a new method is presented to directly measure the dispersion properties of fibers and optical components in the time domain. The analysis is based on pulse shape variations along the tuning range of a theta cavity fiber laser (TCFL) depending on the adjusted repetition rate. The automated measurement procedure, evaluating pulse symmetry, achieves a temporal sensitivity below 5 ps surpassing the resolution of the acquisition electronics. Exemplarily, two samples of Nufern PM980-XP fiber are investigated with an Yb-doped tunable TCFL retrieving the mean dispersion parameter D? by comparative measurements. The obtained results are compared to a reference method based on spectral interferometry. With deviations in D? between either approach of 0.3% and 1.3%, respectively, the results agree well within the measurement errors of the TCFL, verifying the presented concept. Due to the pulse formation process extending over multiple round trips, this approach achieves an enhanced sensitivity compared to competing direct temporal methods. Together with an alignment free operation, the fiber-integrated TCFL depicts a simple and robust concept showing potential in specific measurement scenarios such as in quality management. © 2019 Astro Ltd.
- Item2 MW peak power generation in fluorine co-doped Yb fiber prepared by powder-sinter technology(Washington, DC : Soc., 2020) Leich, Martin; Kalide, André; Eschrich, Tina; Lorenz, Adrian; Lorenz, Martin; Wondraczek, Katrin; Schönfeld, Dörte; Langner, Andreas; Schötz, Gerhard; Jäger, MatthiasWe report on the first, to the best of our knowledge, implementation of a fluorine co-doped large-mode-area REPUSIL fiber for high peak power amplification in an ultrashort-pulse master oscillator power amplifier. The core material of the investigated step-index fiber with high Yb-doping level, 52 µm core and high core-to-clad ratio of 1:4.2 was fabricated by means of the REPUSIL powder-sinter technology. The core numerical aperture was adjusted by fluorine codoping to 0.088. For achieving high beam quality and for ensuring a monolithic seed path, the LMA fiber is locally tapered. We demonstrate an Yb fiber amplifier with near-diffraction-limited beam quality of M2 = 1.3, which remains constant up to a peak power of 2 MW. This is a record for a tapered single core fiber. © 2020 Optical Society of America
- Item(INVITED)Tm:YAG crystal-derived double-clad fibers – A hybrid approach towards high gain and high efficiency Tm lasers(Amsterdam : Elsevier, 2022) Leich, Martin; Müller, Robert; Unger, Sonja; Schwuchow, Anka; Dellith, Jan; Lorenz, Adrian; Kobelke, Jens; Jäger, MatthiasThe hybrid approach of combining a Tm:YAG laser crystal with an amorphous fused silica tube is investigated to evaluate the suitability of the resulting crystal-derived fibers for efficient double-clad fiber lasers. The fabrication process and fiber properties of these Tm fibers are investigated, focusing on the dependence of the active fiber properties on the incorporated Tm3+ concentration. Crystal rods with different doping concentrations (TmxY1-x)3Al5O12 (x = 0.02, 0.05 and 0.08) were used as starting core material for fiber drawing. The investigated fibers are mechanically stable and result in a fairly homogenous and amorphous core glass with optical absorption and emission spectra that are similar to conventional Tm:Al doped silica fibers. Regarding laser properties with 790 nm cladding pumping, we could achieve a maximum slope efficiency of 47% with an output power of 4 W. The fiber laser results are compared to a conventionally fabricated double-clad Tm fiber prepared by Modified Chemical Vapor Deposition and solution doping. To the best of our knowledge, we demonstrate the highest laser output and the highest efficiency obtained from a Tm:YAG crystal-derived fiber.
- ItemObservation of direction instability in a fiber ring laser([London] : Macmillan Publishers Limited, part of Springer Nature, 2021) Arshad, Muhammad Assad; Hartung, Alexander; Pratiwi, Arni Candra; Jäger, MatthiasWe report on the observation of a new phenomenon occurring in a fiber ring laser. This phenomenon is about the transition from an initially bidirectional emission of a reciprocal fiber ring laser to a unidirectional emission at a certain pump power threshold. In addition, the final direction is not predefined but appears to be randomly chosen every time the threshold is exceeded. Therefore, we term this new phenomenon direction instability. Furthermore, we provide a first discussion of how the instability threshold is influenced by the length and the loss of the cavity. We show that the threshold follows a power times length scaling, indicating a nonlinear origin.