A multimode Raman fiber amplifier and method for generating high levels of laser output power from arbitrary pump laser wavelengths using Stimulated Raman Scattering (SRS) in optical fibers of a dual clad design. The optical fibers are amplified in such a manner that facilitates high power, improves brightness conversion, increases conversion efficiency, effectuates lower laser pump brightness, and increases output beam quality. The invention includes a signal core which can support an arbitrary multimode signal from a pump laser, an SRS pump core, and low index outer cladding. The refractive indices of the aforementioned are designed to propagate SRS along the length of the optical fiber.