Thulium-doped all-fiber laser oscillator with more than 100 W of output power at 1940 nm and study of self-pulsing behaviour

We report on the generation of -117 W of CW output power directly from an all-fiber Thulium-doped fiber (TDF) laser oscillator at -1940 nm with a slope efficiency of -53.8%. Optimization of the length of the gain fiber to obtain stable CW output power at 1940 nm has been done by performing self-pulsing studies in different cavity configurations. It has been found that the intensity of the self-pulses are higher in longer length of the TDF, which results in catastrophic damage of the gain fiber, whereas in smaller lengths of the gain fiber, the self-pulses get completely vanished at sufficiently high value of the pump power. Experimental results show that the higher signal re-absorption near 1940 nm along the length of the TDF is responsible for self-pulsing behavior. Optimization of cavity configuration for removal of self-pulses, proper thermal management of TDF and splice joints paved the way for generation of more than -100 W of output power at -1940 nm. This all-fiber Tm-doped fiber laser is promising for medical field applications and plastic welding.