Fig. 1. (a) The experiment device diagram of the compact 3 μm gain-switched laser with an all-fiberized structure. Inset: actual photo of the fiber end-facet mirror M. (b) Measured transmission optical spectrum of the M.

Fig. 2. Under various pump powers and a fixed 20 kHz repetition rate, measured (a) stable gain-switched multi-pulse trains, (b) typical output optical spectra, (c) broadband RF output spectra, and (d) RF spectra at the fundamental frequency peak from the 2 m long fiber laser.

Fig. 3. Temporal pump and gain-switched multi-pulses in one period produced by 2 m long fiber laser under different pump powers of (a) 79 mW, (b) 100 mW, (c) 238 mW, (d) 286 mW, (e) 342 mW, (f) 429 mW, (g) 504 mW, (h) 597 mW.

Fig. 4. Measured (a) stable gain-switched multi-pulse trains and (b) broadband RF output spectrums. (c) Optical spectrums at a 20 kHz pump repetition rate from the 0.25 m long fiber laser. (d) The relationships between average output power and pump power of two kinds of cavities.

Fig. 5. Output characteristics from the 2 m long cavity. Stable gain-switched single-pulse trains at (a) "1-1" state and (b) "2-1" state was generated with increased pump repetition rate. (c) The required pump power and pulse energy threshold varied with the pump repetition rate at different temporal states, respectively. (d) Output optical spectrums at different laser repetition rates, where dash lines represent "2-1" state and solid lines represent "1-1" state.

Fig. 6. Performance characteristics from the 0.25 m long cavity.(a) With increasing pump repetition rate, stable gain-switched single-pulse trains were generated at "1-1" state. (b) Measured pump power threshold and calculated pump pulse energy under various pump repetition rate at "1-1" state, respectively. (c) Output optical spectrums at different laser repetition rates.

Fig. 7. Output characteristics obtained from 2 m and 0.25 m long cavities, respectively.Both (a) and (c) are pulse durations, (b) and (d) are average output powers, single pulse energies, peak powers measured with different pump repetition rates, Inset: single pulse waveform in one period.

Fig. 8. Output single pulse waveforms with or without the output coupler for different fiber lengths and repetition rates of (a) 2 m, 20 kHz, (b) 2 m, 16 kHz, (c) 0.25 m, 20 kHz, (d) 0.25 m, 10 kHz.

Fig. 9. Optical spectrums measured from the MIR gain-switched laser for different fiber lengths and pump powers of (a) 2 m, 110 mW, (b) 0.25 m, 670 mW, under 20 kHz pump repetition rate.