Effects of angle dispersion and fabrication errors of gratings on beam characteristics of spectral combining systems
Considering the beam divergence,the angle dispersion and the fabrication errors of groove angle of the grating and using ray tracing method,the calculation model for the phase change of the laser beam obliquely incident on the grating has been built up.Then,making use of the diffraction integral method and the principle of incoherent superposition of laser beams,the analytical expression for the output intensity distribution of each emitter after passing through the spectral beam combining system has been derived.Finally,according to the intensity second-order moments method,the M2-factor of the combined beam has been calculated and the efffects of the angle dispersion and the fabrication errors of grating groove angle on the beam characterristics of the spectral combining system have been analyzed quantitatively.The results show that the angle dispersion and the fabication errors of grating groove angle will both degrade the beam quality of combined beam,and the effect of the latter on the beam quality of combined beam is more obvious than that of the former.