The present invention relates generally to devices for the generation and amplification of electromagnetic energy. The present invention relates more particularly to optical fiber devices, such as lasers and amplifiers, useful for generating and amplifying optical energy. Accordingly, one aspect of the present invention is an optical fiber device for providing optical gain at a selected wavelength, the optical fiber device comprising: one or more sources of optical pump energy; a first length of optical fiber having a core comprising a first cross-sectional region within which the concentration of a rare earth does not fall below 50% of its highest concentration; and a second length of optical fiber comprising a core comprising a first cross-sectional region within which the concentration of the rare earth does not fall below 50% of its highest concentration, wherein the intensity of optical pump energy is higher in the first length of optical fiber than in the second, and the first cross-sectional region of the core of the second length of optical fiber is larger in area than the first cross-sectional region of the core of the first length of optical fiber.