Multimode diode-pumped graded-index fiber Raman laser with pulsed generation in all-fiber scheme

We report on a pulsed regime of Raman laser with all-fiber cavity scheme based on a multimode graded-index fiber directly pumped by a CW multimode laser diode. The cavity was performed with 3.7 km 62.5/125 MM graded-index fiber with two FBGs on the both sides of it. Intra-cavity acousto-optic modulator pigtailed with 10/125 fiber allowed to obtain mode locking regime. At 27.19-kHz repetition rate corresponding to the laser cavity round-trip frequency (corresponding to mode-locking regime), stable nanosecond pulses with 6.3 W peak power have been observed at the 1st (1018 nm) Stokes order. The beam quality of generated pulses is greatly improved as compared to that for pump diode (M2<20) reaching M2=2.86 for the 1st Stokes and M2=2.08 for the 2nd Stokes beams.