1.2 μm cascaded Raman fiber oscillator exceeding 1.3 kW

High-power fiber lasers operating in the 1.2 μm wavelength region are critical for mid-infrared pump sources and nonlinear frequency conversion applications. However, generating coherent emission at this specific wavelength using rare-earth (RE) doped fiber lasers encounters notable technical obstacles. Among the diverse approaches explored, cascaded Raman fiber lasers (CRFLs) emerge as a particularly promising strategy. This study demonstrates cascaded Raman lasing in a purely passive graded-index (GRIN) fiber configuration, leveraging two pairs of fiber Bragg gratings and cascaded Raman gain under 1080 nm pumping. The output power of the second Stokes component at 1185 nm with a 3-dB linewidth of 1.65 nn has exceeded 1.3 kW, marking the first kilowatt-level cascaded Raman fiber oscillator demonstrated in the 1185 nm wavelength band. Beam quality analysis confirms >80 % fundamental mode content at 1.3 kW, enabling high-brightness applications despite multimode fiber architecture. This achievement not only validates the feasibility of cascaded Raman conversion for realizing high-output power fiber lasers in the 1.2 μm band but also provides a viable approach and significant reference for developing high-power laser sources in other extended wavelength regions.