3.1–5.2 μm Coherent MIR Frequency Comb Based on Yb-Doped Fiber Laser

An offset-free, wavelength-tunable, and midinfrared frequency comb working at 184 MHz based on difference frequency generation (DFG) in a PPMgSLT crystal was demonstrated. A coherent Raman soliton pulse and Yb-fiber laser output were used as the seed pulses of DFG, and wavelength tunability in the range 3.1-5.2 μm was realized. A quantum cascade laser stabilized by the absorption line of N ₂ O was used to measure the beat signal with an MIR comb. The MIR comb had a good spatial beam profile, and a high signal-to-noise ratio (SNR) of 70 dB at a wavelength of 4.52 μm was confirmed. A stable and sharp beat signal was observed in the MIR region with a linewidth of 160 kHz, and the SNR was larger than 20 dB.