Passive coherent beam combining of two femtosecond fiber chirped-pulse amplifiers.

We propose and demonstrate an architecture that achieves passive coherent combination of two femtosecond fiber chirped-pulse amplifiers. The setup consists in the use of a well-balanced amplifying Sagnac interferometer. The experiment shows that the temporal, spectral, and spatial qualities of each beam are retained, with the generation of 250 fs pulses at 35 MHz repetition rate, an uncompressed average power of 10 W, and a combining efficiency of 96%. The behavior of this architecture in the presence of high accumulated nonlinear phase is investigated.