  An ultrafast fiber chirped-pulse amplification laser system based on coherent
combination of 16 ytterbium-doped rod-type amplifiers is presented. It
generates 10 mJ pulse energy at 1 kW average power and 120 fs pulse duration. A
partially helium-protected, two-staged chirped-pulse amplification grating
compressor is implemented to maintain the close to diffraction-limited beam
quality by avoiding nonlinear absorption in air.
