High-pulse-energy actively Q-switched Tm3+-doped photonic crystal fiber laser operating at 2050 nm with narrow linewidth

An actively Q-switched diode-pumped Tm3+-doped fiber laser (TDFL) operating at 2050 nm is reported based on a flexible photonic crystal fiber (PCF) with a core diameter of 50 mu m. Using a fiber length of 3 m, the TDFL delivers Gaussian-shaped pulses with a maximum pulse energy of 1.5 mJ, corresponding to a peak power of 16 kW and a pulse width of 88 ns. The measured output spectrum shows a single peak at 2050 nm with a 3-dB-linewidth of 100 pm and a 10-dB-linewidth of 270 pm. For a longer fiber length of 7 m, the effective gain is redshifted by reabsorption, increasing the achievable pulse energy up to 1.9 mJ. The average output power of the pulsed TDFL can be scaled to more than 100 W with a slope efficiency of 46 %. In all configurations, the TDFL delivers nearly diffraction-limited beam quality (M-2 <1.3).