Coherent combination of two Tm-based fiber amplifiers at sub-ps pulse duration

Any ultrafast laser or amplifier architecture comprises power-scaling limitations, which often originate from thermal or nonlinear effects. Instead of surmounting these issues within a single amplifier or laser design, the spatial separation of the amplification process to individual amplifier channels and the subsequent coherent combination can enable peak and average powers far beyond the limits of a single amplifier. In the context of ultrafast fiber lasers and amplifiers the achievable peak power is limited by the onset of detrimental nonlinear effects and the maximum achievable average power appears to be limited by mode instabilities. Parallelization of multiple fiber amplifiers and coherent combination has already led to a record peak power of 22 GW in combination with 230 W average power from a fiber-based CPA system in the 1 µm wavelength regime [1].