Experimental research on overshoot pump modulated quasi-CW thulium-doped fiber laser around 1940 nm

Thulium-doped fiber lasers have been of interest in many fields including medical surgery, remote sensing and material processing. Because of the nonlinear effect and photodarkening effect, it is difficult to achieve high power laser output in the monolithic laser cavity under continuous wave (CW) mode. In a laser diodes (LDs)-pumped monolithic fiber laser, a pulse laser with a higher peak power than that in CW mode can be realized through the key technique of “overshoot pump modulation”. By applying overshoot pump modulation to 6 LDs at 793 nm to pump the thulium-doped fiber in the laser resonator, we obtained a pulse laser output with a frequency of 10 Hz and a pulse duration of 10 ms. Spectral data revealed that the laser wavelengths in CW mode and pulse mode are both around 1940 nm. On this basis, a peak output power of 515 W in the pulse mode and an average output power over 50 W in the CW mode can be experimentally reached. The output laser pulse waveform is basically consistent with the pump waveform of the diodes, and there is a small delay between them. In this work, the frequency and pulse duration of quasi-CW thulium-doped fiber laser around 1940 nm will be continuously improved anyway as the next step.