Fiber amplifier CPA system using divided-pulse amplification for multi-mJ extraction

Ytterbium-doped fiber chirped-pulse amplification (FCPA) systems have seen an unprecedented power development in recent years. Thus, nowadays they are capable of producing multi-GW peak powers at pulse energies beyond one millijoule [1]. In order to avoid both nonlinear pulse distortions and optically induced damage in these systems, the intensity inside of the signal core of the amplifying fiber has to be reduced by many orders of magnitude. This is achieved by employing fibers with extremely large mode-field diameters (MFDs) and by using largely stretched pulses. However, the scaling of the MFD is typically restricted by production tolerances of the particular fiber design. On the other hand, the geometrical dimension of the laser system typically restrict the attainable stretched pulse durations. The performance of femtosecond FCPA systems could be further improved by using spatially [2] or temporally separated amplification, the latter approach also known as divided -pulse amplification (DPA) [3]. Up to now in DPA the separation of the pulses was usually limited to a few picoseconds