Optimization of pulsed thulium fiber pre-amplifier with wavelength of 1908.06 nm

We researched and optimized the output characteristics of the pulse seed laser and the pre-amplifier. Based on acoustooptic external modulation technology, the effects of forward, backward, and bidirectional pumping modes on the output power and Amplified Spontaneous Emission(ASE) suppression of the pre-amplifier stage are studied. Using optimum fiber lengths of 3.0 m and 1.5 m in seed laser and pre-amplifier, the maximum laser output power of 1.41 W and the slope efficiency of ~16.3% operated at 1908.06 nm are achieved at a repetition rate of 1 MHz and a duty cycle of 80%, respectively. The ASE suppression ratio of 40.0 dB with the input pumping power of 10.88 W is achieved. In the pre-amplifier laser, no self-oscillation or nonlinear effects were observed, indicating that the incorporation of the pre-amplification structure can effectively suppress ASE. The dependence of the amplifier performances on optimum fiber length are also discussed in this paper.