Energy scalable, offset-free ultrafast mid-infrared source harnessing self-phase-modulation-enabled spectral selection.

We demonstrate a high-power offset-free ultrafast mid-infrared (IR) laser source based on difference-frequency generation (DFG). Powerful signal pulses are obtained by filtering the rightmost spectral lobe of the optical spectra broadened by fiber-optic nonlinearities dominated by self-phase modulation. The resulting mid-IR pulses are tunable from 7 to 18 μm with up to 5.4 mW average power. We experimentally and numerically investigate power scaling of this DFG source and demonstrate that increasing the signal power is an efficient approach for generating high-power mid-IR pulses.