3.5 kW four-channel coherently combined ultrafast fiber laser

Power scaling of ultrafast fiber lasers has been accelerated by coherent beam combination [1]. Persisting challenges regarding the average power, i.e. mode instabilities, or regarding the peak power, i.e. high nonlinear phase, can be easily overcome by using several parallel amplifiers in a stabilized interferometer configuration. In this contribution, we present a new record average power for ultrafast laser systems enabled by coherent beam combination and the use of partially-reflective dielectric mirrors as high-power compatible combining element.