Spontaneous Raman emission: an avenue for generating high-power incoherent light sources

Spontaneous Raman emission (SpRE), traditionally viewed as a detrimental effect, impairing spectral purity and imposing fundamental limits on power scaling in conventional fiber lasers, is being harnessed as a novel mechanism to realize high-power incoherent light sources. Compared to previous methods that rely on rare-earth-doped amplified spontaneous emission (ASE), this approach offers superior cost-effectiveness and inherent wavelength flexibility, enabling access to unconventional spectral regions critical for emerging applications like photonic computing and optical coherence tomography (OCT). As a demonstration, we first generate SpRE in a passive fiber segment, and then efficiently amplify this incoherent seed via stimulated Raman scattering to achieve high-power output. The resulting fiber source operates at 1116 nm with 23.03 W output power, 8.24 nm 3 dB bandwidth, and 60.6% optical-to-optical efficiency while exhibiting high temporal stability. The incoherent nature eliminates interference artifacts and makes this source highly favorable for applications such as laser-driven inertial confinement fusion, photonic computing, and OCT.