Coherently combined fiber laser system delivering 120 μJ femtosecond pulses

We report on the coherent combination of two chirped pulsed fiber lasers. The beams coming from two 100 mu m core diameter ytterbium-doped rod-type fibers were coupled in a Mach-Zehnder-type interferometer by means of a polarization beam splitter. Active stabilization of the interferometer was achieved by using a piezo-mounted mirror driven by a Hansch-Couillaud polarization detection system. Pulses with 120 mu J energy and a compressed duration of 800 fs were obtained. This, compared with the 66 mu J coming from each single amplifier, results in a combining efficiency as high as 91%. (C) 2011 Optical Society of America