Revising power scaling limits of diffraction-limited fiber amplifiers

An empirical TMI threshold formula is derived based on a recently developed model and used to analyze the power-scaling performance of ytterbium-doped silica glass and YAG (Y₃Al₅O₁₂) and Lutetia (Lu₂O₃) single-crystalline fiber amplifiers. Overall, the single-crystalline fiber lasers are found to scale potentially to higher average powers mostly due to their higher thermal conductivities compared to silica glass. This work serves as a useful extension to earlier works and shines significant new light on optimal fiber and amplifier designs for maximum average output power with TMI considered.