We report on the feasibility of MIL-101(Cr) (MIL: Materials of Institute Lavoisier) and MIL-101(Cr)-NH2 as novel saturable absorbers for the development of passively Q-switched nanosecond mid-infrared fiber laser systems. The MIL101(Cr) and MIL-101(Cr)-NH2 are prepared using hydrothermal synthesis method and their modulation depths are measured to be 24.09% and 22.83%, respectively. We employ them separately as SAs to achieve passively Q-switched fiber lasers operating at 2.8 μm, for the first time, to the best of our knowledge. Stable Q-switched pulse operation is realized with the shortest pulse duration of 0.75 μs at a repetition rate of 162.58 kHz when using MIL-101(Cr) as a SA. It generates the maximum average output power of 524.4 mW, pulse energy of 2.72 μJ and peak power of 3.43 W at the launched pump power of 3.64 W. In addition, we replace the MIL-101(Cr) with MIL-101(Cr)-NH2 and nanosecond pulses with a pulse duration of 0.79 μs and average output power of 479.5 mW are obtained. The corresponding pulse energy and peak power are 2.27 μJ and 2.87 W, respectively. Our results show that the MIL-101(Cr) and MIL-101(Cr)- NH2 are promising stable SAs for nanosecond laser pulses generation at 3 μm.
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