Fig. 1. Experimental setup of the Fe2+:ZnSe crystal passively Q-switched Er3+-doped ZrF4 fiber laser tunable around 3.5 μm. DM1–DM4, four DMs; L1–L6, six lenses.

Fig. 2. Q-switched pulse train and single pulse waveform (inset) at different launched 1981 nm pump powers. (a) 2.24 W, (b) 2.78 W, (c) 4.19 W, and (d) 5.25 W. (Plaunched 976 nm=2.47  W.)

Fig. 3. (a) Optical and (b) RF spectra at the launched 1981 nm pump power of 5.25 W. (Plaunched 976 nm=2.47  W.)

Fig. 4. (a) Repetition rate and pulse width; (b) average power and pulse energy as functions of the launched 1981 nm pump power. (Plaunched 976 nm=2.47  W.)

Fig. 5. Optical spectrum and output average power with the tuned wavelength. (Plaunched 1981 nm=5.25  W, Plaunched 976 nm=2.47  W.)

Fig. 6. (a) Repetition rate and pulse width; (b) peak power and pulse energy as functions of the tuned wavelength. (Plaunched 1981 nm=5.25  W, Plaunched 976 nm=2.47  W.)