Fig. 1. Experimental setup for the mid-infrared difference-frequency generation based on the synchronous pulse induction. The pump source was provided by an Yb-doped fiber laser, which could deliver all-polarization-maintaining ultrashort pulses due to the passively mode-locked mechanism based on the nonlinear amplifying loop mirror. The pulse energy was improved using cascaded fiber amplifiers. A small portion of the output was detected by a fast photodiode to generate the synchronous electrical signal, which drove the electro-optic modulator to implement the intensity modulation on a continuous-wave laser at the telecom wavelength. Finally, the temporally synchronized pump and induction pulses were combined and then focused into the nonlinear crystal, thus leading the generation of the MIR ultrashort pulses via the nonlinear DFG

Fig. 2. (a) Output spectra for the Yb-doped fiber laser at various average powers; (b) Autocorrelation trace for the pump pulse at the average power of 6.2 W; (c) Output spectra of continuous-wave laser with a tuning rage of 1527-1565 nm; (d) Temporal envelope of the generated induction pulse from the fast intensity modulator; (e) MIR laser spectra for different pump average powers, the power of the induction pulse was fixed at 500 mW; (f) Cross-correlation trace between the pump and induction pulses via nonlinear difference-frequency generation

Fig. 3. (a) MIR average power and conversion efficiency as a function of the pump power; (b) Long-term stability for the MIR output power, σ denotes the relative fluctuation

Fig. 4. (a) MIR power as a function of the pump intensity for various seed pulse powers; (b) Dependence of the MIR power on the seed pulse intensity at various pump powers

Fig. 5. By changing the output wavelength of the continuous-wave laser, the central wavelength of the MIR source could be continuously tuned from 3000 to 3175 nm