 Much progress has been made in the power scaling Lasers and Amplifiers produced with ytterbium ( Yb ) doped optical fibers . Power levels have increased from the 1 kW regimes due to the advancements in components as well as the Yb doped fibers themselves . Fabrication of Low NA , Large Mode Area ( LMA ) fibers enable achievement of near perfect beam qualities ( M2 < 1 @.@ 1 ) at power levels of 1 @.@ 5 kW to greater than 2 kW at ~ 1064 nm in a broadband configuration . Ytterbium @-@ doped LMA fibers also have the advantages of a larger mode field diameter ( MFD ) which negates the impacts of nonlinear effects such as stimulated Brillouin scattering ( SBS ) and stimulated Raman scattering ( SRS ) , which limit the achievement of higher power levels , and provides a distinct advantage over single mode ytterbium @-@ doped fibers . 
