Power and energy scaling of Tm-doped fiber lasers enabled by in-band pumping

This is the authors' abstract. We don't add key points for this paper.

In this work, we report on the average-power scaling of high-energy, Tm-doped fiber laser systems using in-band pumping at 1650 nm. Compared to conventional 790 nm pumping, the in-band pumping approach significantly reduces the quantum defect and, consequently, the thermal load. This allows for achieving previously unattainable combinations of high pulse energy and high average power with excellent beam quality and high slope efficiency from a Tm-doped fiber. To illustrate this, we demonstrate 9 mJ pulse energy (with 81 ns pulses) at 60 kHz repetition rate (corresponding to 540 W average power) with 75% slope efficiency from a rod-type, Tm-doped fiber amplifier—a new performance record for this architecture. Additionally, we also reached 1.2 kW of average power with 3 mJ pulse energy (using 800 ns pulses) and 80% slope efficiency using a bendable, Tm-doped, photonic-crystal fiber. Moreover, using this same fiber in pure continuous-wave operation, we achieved a pump-power-limited output power of up to 1.4 kW, also with 80% slope efficiency. This is the highest output power reported so far from any single-channel fiber laser system in the 2 µm wavelength region.