Analysis of Raman and thermal effects in kilowatt fiber lasers

A theoretical analysis of Raman and thermal effects in kilowatt ytterbium-doped double-clad (YDDC) fiber lasers is presented. Solutions to suppress these detrimental effects in the YDDC fiber lasers under bidirectional end pump and distributed pump are discussed. The quantitative analysis shows that the Raman effects can be suppressed by using large-mode-area fibers, shortening the cavity length, adopting a longer lasing wavelength, and reducing reflections at the Raman–Stokes wavelengths; and the thermal effects can be effectively eliminated by utilizing the distributed pump and optimizing the arrangement of pump powers, pump absorption coefficients, and fiber lengths.