Raman suppression within the gain fiber of high-power fiber lasers.

We report the effective suppression of Raman emission in a monolithic ytterbium-doped fiber laser by the insertion of a chirped and tilted fiber Bragg grating (CTFBG) directly within the gain fiber of the laser. In comparison with a non-compensated filtered laser cavity for which the Raman threshold occurs at an output power of 1.54 kW, the insertion of a CTFBG within the gain medium leads to an increase in the Raman threshold by 260 W. We also demonstrate that the insertion of a CTFBG in between a laser cavity and a passive beam delivery fiber leads to an increase in the Raman threshold by 100 W with respect to the non-compensated case.