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Mid-infrared pulsed fiber laser with centered wavelength from 2 to 5 μm have attracted substantial attention owing to their potential applications in defence, laser microsurgery, material processing, nonlinear frequency conversion, etc. We demonstrated our recent achievements at 3 μm pulsed fiber lasers by utilizing Q-switching method. Firstly, a cascaded dual wavelength actively Q-switched Ho3+-doped ZBLAN fiber was reported by inserting an external electrically driven acoustic-optical modulator (AOM) into the cavity. The 3.0 μm and 2.07 μm pulse trains were achieved with a μs level time delay corresponding to the pulse energy of 29 μJ and 7 μJ, pulse duration of 380 ns and 260 ns, respectively. The narrower pulse width in this case compared to that in passively Q-switched fiber lasers can be attributed to the much higher modulation depth of AOM. Using a reversely designed semiconductor saturable mirror (SESAM) as the saturable absorber (SA), we presented a passively Q-switched Ho3+-doped ZBLAN fiber laser operating at ~2971 nm, the obtained maximum pulse energy of 6.65 μJ only limited by the maximum pump power was also the highest level from passively Q-switched fiber lasers at this wavelength range, and corresponding pulse repetition rate and duration were 47.6 kHz and 1.68 μs, respectively. Then using a Fe2+: ZnSe crystal with an initial transmission of 69 % as the SA, a passively Q-switched Ho3+-doped ZBLAN fiber laser operating at 2970.3 nm was also achieved. The obtained pulse duration and repetition rate were 1.92 μs and 62.74 kHz, respectively with an output power of 266 mW and a pulse energy of 4.24 μJ. The further performance improvements were possible because they were just limited by the maximum pump power. To sum up, the above achievements would be beneficial for further development of mid-infrared pulsed fiber lasers.
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