  An ultrafast laser based on coherent beam combination of four ytterbium-doped
step-index fiber amplifiers is presented. The system delivers an average power
of 3.5 kW and a pulse duration of 430 fs at 80 MHz repetition rate. The beam
quality is excellent (M2<1.24x1.10) and the relative intensity noise is as low
as 1% in the frequency span from 1 Hz to 1 MHz. The system is turn-key operable
as it features an automated spatial and temporal alignment of the
interferometric amplification channels.
