Efficient even without cooling

At the 11^th EPS-QEOD (Europhoton) in Vilnius (Lithuania), PhD student Mathias Lenski of the AG Fiber and Waveguide Lasers de was honored for his presentation on In-band pumping of 2 µm Tm:fiber.

His contribution “High-power, air-cooled Thulium doped fiber amplifier with 71 % slope efficiency” received the “QEOD-EPS, Runner-up Best Student ORAL presentation” award. The presentation focused on the benefits of shifting the pump wavelengths due to the quantum efficiency in the active amplification process. The underlying process was discussed theoretically and demonstrated experimentally:

Normally, thulium-doped fibers (Tm fibers) at a pump wavelength of 793 nm have to be cooled, i.e. thermally tethered, at an output power of already 1 W due to the temperature dependence of the absorption and emission cross sections. In the presented experimental setup, however, the Tm-doped fiber, i.e. an optical amplifier, was placed directly in air without thermal management, on three small support points, and due to the lower quantum defect when using an optical pump with a central wavelength of 1692 nm, the heat load in the amplifier fiber could be significantly reduced and a slope efficiency of over 71 % with an average output power of 80 W could be achieved. 

In the theoretical part of his presentation, Mathias Lenski further demonstrated the output power scalability of in-band pumped Tm-doped fiber lasers to multi-kW compared to 793 nm for a specific case.

Mathias Lenski is delighted with the response: “I am really happy about this award and also about the feedback I received during the conference. I share this appreciation with my colleagues, as such results are always a team effort! Together with the award for Jens Limpert and Jan Rothhardt, also here at this conference, this confirms our successful course of setting topics in the international research community.”

Publication:

M. Lenski, T. Heuermann, Z. Wang, C. Aleshire, C. Gaida, C. Jáuregui, and J. Limpert, "In-band pumped, Q-switched thulium-doped fiber laser system delivering 140 W and 7 mJ pulse energy," Opt. Lett. 49, 4042 (2024).External link