Influence of thermal deformation of a multilayer dielectric grating on a spectrally combined beam.

In spectral beam combining (SBC) systems, temperature rise inevitably happens to the multilayer dielectric grating (MDG) due to irradiation of the high-power continuous-wave (CW) laser, resulting in thermal deformation of the MDG and degradation of the characteristics of the combined beam due to thermal deformation of the grating. The calculation model of thermal deformation of the MDG has been proposed, and the distributions of temperature field and thermal deformation of the grating have been analyzed. On this basis, a propagation model of a SBC system has further been built up. By utilizing the diffraction integral method and the principle of incoherent superposition, the intensity distribution and the beam quality of the combined beam with different power densities based on the MDG have been numerically calculated and analyzed in detail. The results show that both the maximum temperature rise and the thermal deformation of the MDG increase dramatically with the increasing power density of the incident laser beam. Side lobes appear in the intensity distribution of the combined beam due to thermal deformation of the MDG. Furthermore, the side lobes of the combined beam become increasingly obvious with increasing power density. Additionally, the beam quality of the combined beam degrades significantly with increasing power density of the incident laser beam.