Fig. 1. Principle diagram of 3.8 μm laser output by using DFG

Fig. 2. Principle diagram of cladding-pumped all-polarization Yb-doped fiber mode-locked laser

Fig. 3. Principle diagram of 1094 nm laser pump source obtained by two stage amplification of gain modulated self-seeded LD output pulse

Fig. 4. Output power dependence of 3.8 μm laser on the 1094 nm pump power at optimum operating temperature of 51 ℃. (a) Mode-locked pulse seed; (b) gain modulated LD pulse seed

Fig. 5. Pulse waveform of laser output. (a) 1094 nm from direct mode-locked output; (b) 1094 nm after fiber amplification; (c) 1535 nm before DFG; (d) 1535 nm after DFG