Successful in San Francisco

Three of our researchers received "Best Student Presentation Awards" at this year's SPIE Photonics West in San Francisco for the particular scientific relevance and quality of their presentations, two of them doing research at the "Waveguide & Fiber Lasers" working group, the other winner is working at our partner institute Fraunhofer IOF.

The annual highlight for the international optics and photonics community is undoubtedly the largest conference in this field - SPIE Photonics West. In addition to the presentation of the latest scientific achievements, it has its appeal due to the friendly weather at the end of January (30 January to 1 February 2024) and surely the city of San Francisco itself. In this positive climate, numerous representatives from science and industry from all over the world exchange ideas not only at a trade fair but also at sub-conferences, such as "Frontiers in Ultrafast Optics: Biomedical, Scientific, and Industrial Applications XXIV" and "Fiber Lasers XXI: Technology and Systems", at which our researchers from the Leistungszentrum Photonik were represented.

The outstanding scientific results and their presentation by Maximilian Karst (IAP), Friedrich Möller (IOF) and Mathias Lenski (IAP) impressed the conference committees and were honoured accordingly with "Best Student Presentation Awards".

Innovative research results in the field of fibre lasers and ultrafast optics

Maximilian Karst presented in "Pulse quality improvement in multipass cells through dispersion engineering" an experimental demonstration of enhanced-frequency-chirping (EFC) in a multipass cell (MPC) based post-compression scheme through dispersion engineering. The transfer of the nonlinear interaction into the EFC regime enables a smooth spectrum void of strong modulations as they occur in regular self-phase modulated spectra. The resulting 32 fs pulses exhibit minimal side features, with more than 96 % of energy contained in the temporal main feature. The experiments were performed with an mJ-class Yb:fibre laser with a repetition rate of 50 kHz at average power of 70 W. The results show the extended possibilities for dispersion-tailored pulse propagation in MPCs [1]. The doctoral student from Prof Jens Limpert's working group thus took first place in the "Frontiers in Ultrafast Optics Best Student Paper Competition".

Second place in the "Fiber Lasers Best Student Oral Paper Competition" went to Friedrich Möller, researcher in the Laser and Fiber Technology department at Fraunhofer IOF, on the topic of "Spectral beam combining of kW-class thulium-doped fiber lasers". His work presents an approach to significantly increase the power of kW-class thulium-doped fiber amplifiers (2030-2050 nm) around 2 μm wavelength by use of dual-grating spectral beam combining (SBC). The amplifiers consist of three stages and are pumped with non-stabilized, fiber-coupled diode lasers at 790 - 795 nm. Singlemode, TMI-free output powers exceeding 800 W, with narrow linewidths of FWHM ⪅115 pm, were achieved and subsequently combined using highly efficient in-house fabricated reflection gratings. With an overall combining efficiency of 90 % and a thermal slope of the combining grating measured as 6.8 K/kW, scalability to kW-level powers is enabled. The combined output power achieved a record-breaking 1.91 kW with good beam quality (M2 ⪅2) and potential for further optimization. [2].

At the same symposium, Mathias Lenski achieved third place with his research results on the topic of "Highly efficient, in-band pumped, thulium-doped, Q-switched fiber laser". High-power laser sources in the 2 μm wavelength range and emitting ns pulses are at the center of research here, as these have great potential for numerous applications in materials processing, biology and for laser plasma sources targeting the extreme ultraviolet range. Thulium (Tm)-doped fibers represent a very attractive platform for Q-switched systems emitting ns pulses in the 2 μm wavelength range. Usually, high-power, Tm-doped fiber amplifiers are pumped at 790 nm. By exploiting Cross-Relaxations (CR) the slope efficiency can be significantly increased beyond the Stokes limit. However, in those fiber systems targeting mJ pulse energy, the slope efficiency is barely above 35 %. Due to the large quantum defect of approximately 60 % such systems face considerable thermal challenges. In this contribution an in-band pumped Q-switched oscillator is demonstrated. This source is used to seed an in-band pumped, Tm-doped, rod-type amplifier which delivers up to 6.1 mJ pulse energy and up to 128 W average power with 77% slope efficiency [3].

[1]    Maximilien Karst (IAP): “Pulse quality improvement in multipass cells through dispersion engineering”External link1st place at Subconference "Frontiers in Ultrafast Optics: Biomedical, Scientific, and Industrial Applications XXIV”

[2]    Friedrich Möller (IOF): „Spectral beam combining of kW-class thulium-doped fiber lasers“External link, 2nd place at Subconference “Fiber Lasers XXI: Technology and Systems”

[3]    Mathias Lenski (IAP): „Highly efficient, in-band pumped, thulium-doped, Q-switched fiber laser”External link, 3rd place at Subconference "Fiber Lasers XXI: Technology and Systems”, 

Further information about the Fraunhofer IOF can be found at: www.iof.fraunhofer.deExternal link