Existing material and other constraints preclude the creation of diffraction-limited continuous-wave fiber lasers or amplifiers with an output of greater than about 36 kW, according to a theoretical analysis done by researchers at Lawrence Livermore National Laboratory (Livermore, CA). The analysis, which relies on physical limits such as thermal limitations, nonlinear optical effects, output-end limitations, and pump-power limitations (and excludes multiple-laser schemes such as coherent beam combination), unavoidably includes assumptions and approximations, but should give a good idea of the scalability of various fiber-laser parameters (see Dawson et al., Optics Express, p. 13240, Aug. 18, 2008).
Assuming fused silica as the laser material and varying different parameters including core diameter, fiber length, fiber bend radius, pump wavelength, doping concentration, and others, the researchers considered two cases: broadband, for which stimulated Brillouin scattering (SBS) need not be considered, and narrowband, for which SBS is relevant. For broadband, the upper limit was 36.6 kW; for narrowband, 1.86 kW. The authors note that the derivation they developed is what they consider most important; the actual numbers may change with improvements in technology (such as fibers that can suppress stimulated Raman scattering). Contact Jay Dawson at [email protected].