Fig. 1. Experimental setup of the all-fiber gain-switched TDFL and the associated PAM system. COL, collimator.

Fig. 2. (a) Output power evolution of the lasers with regards to the enhancement of the pump power. (b) Superimposed optical spectra of the gain-switched TDFLs at 1700, 1725, and 1750 nm under the maximum pump power of 3 W; inset: zoom-in spectrum of the 1725 nm laser.

Fig. 3. (a) Pulse waveform of the 1725 nm laser with maximum output power. (b) Pulse waveform, (c) pulse train over 1 ms, and (d) histogram of around 2000 pulses after 60 MHz low-pass filtering; inset of (d): corresponding pulse train over 0.2 s.

Fig. 4. Measured (a) lateral and (b) axial resolution of the PAM system by scanning the edge of a black tape, of which the thickness is 100 μm.

Fig. 5. (a) Fat beef slice used for PAM imaging. (b) The obtained 3D imaging and (c) MAP imaging by scanning the box section in (a).