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  2. Over 400 W average power, sub-two-cycle, carrier-envelope phase-stable fiber laser system

    Authors
    I. Seres, E. Shestaev, M. Tschernajew, P. Jójárt, C. Gaida, N. Walther, T. Bartyik, B. Gilicze, Z. Bengery, D. Hoff, M. Kienel, T. Eidam, J. Limpert, Á. Börzsönyi, K. Varjú, Z. Várallyay
    Year of publication
    Published in:
    High Power Laser Science and Engineering
    We report on the development of a carrier-envelope phase (CEP)-stable 1030 nm fiber-based laser system producing 6.2 fs pulses achieved via the multi-pass cell (MPC) post-compression technique with 402 W average power at 100 kHz repetition rate. This system employs an upgraded three-stage MPC compression scheme exhibiting excellent beam quality properties for this intensity region. Active stabilization locks the CEP noise below 430 mrad root mean square. This work represents the first demonstration of a coherently combined fiber laser system simultaneously achieving such exceptional average power, CEP stability and sub-two-cycle pulse durations. Similar to all other light sources of the Extreme Light Infrastructure Attosecond Light Pulse Source, this newly developed system is accessible to the international research community in peer-reviewed open user calls of the Extreme Light Infrastructure European Research Infrastructure Consortium.
    University Bibliography Jena:
    fsu_mods_00035153External link

  3. Transverse mode characterization in optical fibers using singular value decomposition

    Authors
    Y. Tu, C. Pfleghar, C. Jauregui, J. Limpert
    Year of publication
    Published in:
    Optics express
    What we believe to be a new scalar and data-driven approach to experimentally characterize the transverse modes of optical fibers is proposed in this paper. It retrieves the orthogonal modal base set of the fiber via singular value decomposition after collecting a large set of data under different coupling conditions. The results show good agreement with the simulated transverse modes. Due to its operating principle, this approach can characterize any fiber, regardless of its length or size, a prominent advantage compared to other experimental approaches.
    University Bibliography Jena:
    fsu_mods_00035538External link

  4. Unleashing HHG efficiency: the role of driving pulse duration

    Authors
    R. Klas, M. Gebhardt, J. Rothhardt, J. Limpert
    Year of publication
    Published in:
    PhotoniX
    High harmonic generation (HHG) is a crucial technology for compact, high-brightness extreme ultraviolet (XUV) and soft X-ray sources, which are key to advancing both fundamental and applied sciences. The availability of advanced driving lasers, with tunable wavelength, power, and pulse duration, opens new opportunities for optimizing HHG-based sources. While scaling laws for driving wavelengths are well understood, this work focuses on how pulse duration impacts HHG efficiency and introduces a unified framework that links microscopic dynamics to macroscopic performance. We establish a practical scaling law for the single-atom dipole moment under phase-matching conditions, demonstrating a τ-1 dependence at 515 nm wavelength. By connecting this microscopic scaling to macroscopic conversion efficiency, we provide clear guidelines for optimizing HHG output across different gases and driving wavelengths. Furthermore, we identify fundamental constraints, including the carrier-envelope-phase (CEP) walk-off, which limits efficiency at longer driver wavelengths and becomes especially significant for very short pulses. All predictions are based on simple, accessible formulas, eliminating the need for complex numerical simulations. Experiments confirm these predictions and highlight when short pulses are advantageous, particularly in scenarios where CEP walk-off and absorption effects are minimized. These findings offer practical principles for designing next-generation HHG sources, capable of Watt-level average power and extended spectral reach, enabling more versatile and powerful HHG-based XUV and soft X-ray sources.
    University Bibliography Jena:
    fsu_mods_00036364External link

  6. Polarization-maintaining, rod-type, ytterbium-doped, multi-core fiber for high power operation

    Authors
    Y. Khalil, C. Jauregui, A. Klenke, M. Bahri, J. Nold, N. Haarlammert, T. Schreiber, J. Limpert
    Year of publication
    Published in:
    Optics express
    It has been previously observed that each core in a multi-core fiber has its own birefringence properties. Therefore, obtaining a laser output with a well-defined polarization pattern from a multi-core fiber is challenging. In this work, we explain the origin of this core-dependent birefringence and present a polarization-maintaining, 35-core fiber design that is tested in an oscillator setup, delivering over 100W of power with a polarization contrast ratio close to 10dB. This is a significant improvement with respect to a comparable non-polarization-maintaining multi-core fiber.
    University Bibliography Jena:
    fsu_mods_00030211External link

  7. 117-mJ pulse energy, high average power, Q-switched Yb-doped 49-core fiber amplifier

    Authors
    M. Bahri, C. Jauregui, A. Klenke, M. Lenski, J. Nold, N. Haarlammert, T. Schreiber, J. Limpert
    Year of publication
    Published in:
    Optics express
    This work presents the simultaneous scaling of the average power and pulse energy emitted by multicore fiber laser systems. This is achieved through two series of experiments that use a generation of Yb-doped multicore fiber amplifiers with 49 cores, seeded by a Q-switched multicore fiber laser. One of the main results of these experiments is a total pulse energy of up to 117 mJ at a repetition rate of 5 kHz in quasi-continuous pumping operation. In a different experiment with a smaller core size multicore fiber, an average power of 400 W was achieved at a repetition rate of 5 kHz, corresponding to a pulse energy of 80 mJ in continuous pumping. The experimental results match our simulation predictions, providing valuable insights into the further energy scalability of Yb-doped multicore fibers.
    University Bibliography Jena:
    fsu_mods_00030210External link

  8. Single-frame randomized probe imaging in the EUV using a high-order harmonic source

    Authors
    S. Chew, W. Eschen, C. Liu, M. Abdelaal, J. Limpert, J. Rothhardt
    Year of publication
    Published in:
    Optics express
    We report the demonstration of single-frame randomized probe imaging (RPI) using a 13.5 nm extreme ultraviolet (EUV) beam from a table-top high-harmonic generation (HHG) source. Three types of beams—a smooth, vortex, and speckle beam—were used to investigate the effect of different illuminations on image quality. Single-frame RPI reconstructions were successfully achieved for all beam types, with the highest resolution of 110 nm obtained using the EUV speckle beam. Comparisons with ptychography reconstructions confirm the advantages of structured illuminations over a smooth beam, showing improved convergence and image fidelity. Furthermore, averaging a small number of RPI images reconstructed from individual diffraction patterns significantly improves the resolution to sub-100 nm. These results demonstrate the capability of single-frame RPI to deliver rapid, high-resolution EUV imaging, offering a promising approach for applications limited by acquisition time, such as ultrafast pump-probe studies and real-time feedback.
    University Bibliography Jena:
    fsu_mods_00034896External link

  9. Experimental investigations on the relative phase stability in amplifying multicore fibers

    Authors
    F. Wanitschke, C. Jauregui, A. Klenke, Y. Khalil, M. Bahri, J. Limpert
    Year of publication
    Published in:
    Fiber lasers XXIII: technology and systems
    University Bibliography Jena:
    fsu_mods_00036538External link

  10. Recent developments in the understanding and passive mitigation of transverse mode instability

    Authors
    C. Jauregui, Y. Tu, S. Kholaif, F. Möller, G. Palma-Vega, N. Haarlammert, T. Walbaum, T. Schreiber, J. Limpert
    Year of publication
    Published in:
    Optical Fiber Technology: Materials, Devices, and Systems
    In this article we look at the newest developments in the understanding and mitigation of TMI in single-core fibers. This includes recent quantitative measurements that reveal the dependence of the TMI threshold on the modal content of the seed, systematic measurements on the dependence of the TMI threshold on the fiber core size, as well as the study of TMI in PM fibers including a novel passive mitigation strategy and the static modal energy transfer recently observed in these fibers.
    University Bibliography Jena:
    fsu_mods_00029154External link

  11. Multicore-fiber-based, high-power femtosecond CPA laser system with fast dynamic beam shaping capabilities

    Authors
    A. Klenke, F. Wanitschke, M. Bahri, Y. Khalil, C. Jauregui, J. Nold, N. Haarlammert, T. Schreiber, J. Limpert
    Year of publication
    Published in:
    Fiber lasers XXIII: technology and systems
    University Bibliography Jena:
    fsu_mods_00036537External link

  12. Power and energy scaling of efficient in-band pumped Tm-doped fiber lasers

    Authors
    M. Lenski, F. Wanitschke, F. Bontke, C. Gaida, P. Gierschke, M. Bahri, W. Röder, T. Heuermann, C. Jáuregui, J. Limpert
    Year of publication
    Published in:
    Fiber lasers XXIII: technology and systems
    University Bibliography Jena:
    fsu_mods_00036540External link
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