Difference-Frequency Generation of Random Fiber Lasers for Broadly Tunable Mid-Infrared Continuous-Wave Random Lasing Generation

Random fiber lasers (RFLs) can generate flexible near-infrared lasing wavelengths with high power/high efficiency in simple configurations, which could be excellent candidates to realize low spatial and/or temporal coherence mid-infrared (MIR) random lasing via the difference-frequency generation (DFG) process. Here, we explore the feasibility, and demonstrate the proof of concept of MIR continuous-wave (CW) random lasing through DFG of RFLs in a new promising nonlinear optical crystal BaGa
₄
Se
₇
for the first time, to the best of our knowledge. The watt-level ytterbium-doped RFL with the tuning range covering 1038 to 1091 nm and the cascaded random Raman fiber laser at 1213 nm or 1281 nm serve as pump and signal sources, respectively for DFG in a 15 mm-long BaGa
₄
Se
₇
crystal. As a result, we experimentally demonstrate the MIR random lasing with the tuning wavelengths ranging from 5.5 μm to 9.5 μm. The output power of the MIR DFG at 5.6 μm is measured as 26.8 μW with a conversion efficiency of 8.4 μW/W
²
. This work proves that RFLs could provide a new compact and cost-effective platform to realize broadly tunable modeless CW MIR lasers, which can potentially extend the applications of RFLs such as temporal ghost imaging and speckle-free imaging to MIR region.