Brightness enhancement in random Raman fiber laser based on a graded-index fiber with high-power multimode pumping
Yizhu Chen, Chenchen Fan, Tianfu Yao, Hu Xiao, Jinyong Leng, Pu Zhou, Ilya N. Nemov, Alexey G. Kuznetsov, Sergey A. Babin
Abstract
A brightness-enhanced random Raman fiber laser (RRFL) with maximum power of 306 W at 1120 nm is demonstrated. A half-open cavity is built based on a graded-index (GRIN) passive fiber and single high-reflective fiber Bragg grating written in it directly. Due to the beam cleanup effect in the GRIN fiber enhanced in the half-open RRFL cavity, the output beam quality factor <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:msup> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mi mathvariant="normal">M</mml:mi> </mml:mrow> <mml:mn>2</mml:mn> </mml:msup> </mml:mrow> </mml:math> is improved from 9.15 (pump) to 1.76–2.35 (Stokes) depending on power, while the pump–Stokes brightness enhancement (BE) factor increases proportionally to output power reaching 6.1 at maximum. To the best of our knowledge, this is the highest power GRIN RRFL with BE.