Master oscillator power amplifier (MOPA) systems based on double clad (DC) fiber amplifiers are used to generate diffraction-limited laser radiation with a high average power. A fundamental limit to a further increase in power is stimulated Raman scattering (SRS).
To suppress Raman scattering in DC fiber amplifiers, long-period gratings (LPGs) are structured along a fiber. As a result, the Stokes wavelength from the core is injected into the cladding.
The use of one LPG per meter of fiber results in effective attenuation of the Stokes wavelength of 20 dB.
LPGs represent an effective way to increase the power of laser systems. They enable more compact and efficient high-performance lasers for industrial materials processing and in information technology.
D. Nodop, C. Jauregui, F. Jansen, J. Limpert, and A. Tünnermann, "Suppression of stimulated Raman scattering employing long period gratings in double-clad fiber amplifiers," Opt. Lett. 35, 2982-2984 (2010)