3 kW Passive-Gain-Enabled Metalized Raman Fiber Amplifier With Brightness Enhancement

Raman fiber lasers (RFLs) are currently promising and versatile light sources for a variety of applications. So far, operations of high power and brightness-enhanced RFLs have absorbed enormous interests along with rapid progress. Nevertheless, the stable Raman lasing at high power levels remains challenged by the thermal effects. In an effort to realize more effective thermal management in high power RFLs, here we demonstrate for the first time, an all-fiberized Raman fiber amplifier (RFA) based on metal-coated passive fiber enabling high power lasing. By employing aluminum to the coating of graded-index (GRIN) passive fiber, the thermal dissipation of the fiber is more sufficient to support low-temperature but high-power operation. The maximum output power reaches 3.083 kW at 1130 nm with a conversion efficiency of 78.7%. To the best of our knowledge, this is the highest power attained in the fields of Raman lasers based on merely nonlinear gain. Stokes emission in the GRIN fiber enables brightness enhancement (BE) of output laser. Accordingly, the beam quality parameter M
²
and BE value are 3.12 and ~9 when the signal power is 2.364 kW, which reach 5.72 and ~2.9 at maximum power, respectively. As far as we know, we have achieved the highest power record among all the brightness-enhanced Raman lasers in any kind of configurations.