Analysis of the beam characteristics and the propagation model of spectral combining systems for Yb-doped fiber lasers

The propagation model for the spectral combining systems including Yb-doped fiber laser arraystransform lensgrating and output coupler has been built up. By taking into considerotion the grating angle dispersionthe fabrication errors of groove angle and the diffraction efficiency of the gratingthe formula for the phase change of the Gaussian beam unparallelly oblique incidence on the grating and the analytical expression for the intensity distribution of the combining beam have been derived by using the ray tracing methodthe diffraction integral methodthe principle of incoherent superposition of laser beams and the intensity second-order moments method. Consequentlythe effects of the angle dispersionthe diffraction efficiency and the fabrication errors of groove angle of the grating on the beam characteristics of the spectral combining system have been analyzed for the case of Gaussian beam unparallelly oblique incidence on the grating. The results show that the beam quality of the combined beam remains almost the same as that of a single fiber laser. The effect of the angle dispersion of the grating on the beam quality of combined beam can be neglected. The beam quality of combined beam degrades with the increasing of the fabrication errors of groove angle of the grating. For the case of the large fabrication errors of groove angle of the gratingthe effect of the diffraction efficiency of the grating on the beam characteristics of the combined beam should be considered.