Efficient Frequency Comb Generation in the 9- m Region Using Compact Fiber Sources

We demonstrate a midinfrared (mid-IR) frequency comb spanning from 7.5 to 11.6 μm at a -20-dB level using difference frequency generation in a AgGaS₂ crystal with a compact all-fiber source based on Tm³⁺ and Er³⁺-amplifiers. The power of the mid-IR signal is measured to be 1.55 mW and the photon conversion efficiency is 16%. The pulse duration achieved in the mid-IR range is estimated to be ~80 fs, which corresponds to 2.6 optical cycles at the 9.2-μm center wavelength. The current approach allows simple power scaling by further amplification of the pump and signal pulses using established fiber amplifier technologies.