Design of a new family of narrow-linewidth mid-infrared lasers

We describe the design of a new family of high-spectral-brightness narrow-linewidth mid-infrared lasers—of <1  MHz anticipated linewidths—with potential for operation at any target wavelength between 2.5 and 9.5 μm. More specifically, we analyze the potential performance characteristics of mid-infrared distributed-feedback (DFB) Raman fiber lasers (RFLs) based on π-phase-shifted (PPS) fiber Bragg gratings written in appropriately chosen low-phonon-energy glass fibers. In particular, we calculate anticipated threshold pump powers for optimal laser designs and pump wavelengths for single-frequency (fundamental mode) operation of specific mid-infrared DFB-RFLs operating at chosen target wavelengths and show that these pump powers can be as low as a few milliwatts for MIR DFB-RFLs fabricated with appropriate low-loss small-mode-area single-mode fibers. As such, we clearly establish the PPS-DFB-RFL platform as a very practical approach for constructing a broad range of narrow-linewidth MIR coherent sources for numerous applications, including proximal and remote sensing of molecules and various high-spectral-brightness and long-coherence-length MIR applications.