Multifilament-core fibers for high energy pulse amplification at 1.5 microm with excellent beam quality.

We report on what we believe to be the first demonstration of an erbium-ytterbium-doped multifilament-core (MFC) fiber for single-mode amplification of narrow linewidth high peak power pulses. A master-oscillator-power-fiber-amplifier laser source has been demonstrated using a 37-filament MFC fiber in the last amplification stage. Pulses with 750 microJ (940 W peak power) and laser linewidth<1 MHz have beam generated with M2 approximately 1.3. This value is close to the theoretical value M2 approximately 1.5.