Towards coherent combination of 61 fiber amplifiers

Abstract

The XCAN project aims at the coherent combination of 61 ber ampli ers in the femtosecond regime. An important intermediate step towards this goal is the implementation of a seven ber test setup, which allows to address key scienti c and technical challenges which might occur in the scaled version of 61 bers. This work includes the design and characterization of a support unit able to hold 61 bers with the high precision required for an ecient coherent combination in tiled aperture con guration. This con guration, in combination with an interferometric phase measurement and active phase control, is particularly well suited for the coherent combination of a very large number of beams. Our rst preliminary results with seven bers include a combination eciency of 30% and a residual phase error between two bers as low as /40 rms. Experiments conducted with three bers in order to evaluate technical improvements revealed an increase of eciency to 54 %. The combined beam was temporally compressed to 225 fs, which is Fourier transform limited with respect to the measured spectrum.