Time and frequency domain characteristics of a quasi-continuous 2 μm thulium-doped fiber laser

Lasers with wavelengths around 2 mu m are located in the atmospheric transmission window and at the strong absorption peak of water, and have important applications in medicine, LIDAR, material processing, and pump sourc- es for mid-infrared lasers. The thulium-doped fiber laser (TDFL (TDFL) stands out as a critical light source capable of deliver- ing high power outputs at this wavelength. In this paper, to address the problems of relaxation oscillation and inter-mod- al four-wave mixing in a quasi-continuous wave (QCW (QCW) TDFL, the time and frequency-domain output characteristics of the laser are optimized by increasing the bias current, optimizing the length of the gain fiber, and changing the diame- ter of the fiber coiling, etc. The effects of different gain fiber structures on the fiber transmission modes are also investi- gated. The developed QCW-TDFL achieves a peak power of 894 W and an average power of 89. 4 W at a central wave- length of 1 939. 2 nm with a pulse width of 100 mu s, a repetition frequency of 1 kHz and a duty cycle of 10%, and ob- tains stable and controllable pulse output waveform and spectral characteristics.