Optical characterizations and thermal analyses of HfO₂/SiO₂ multilayered diffraction gratings for high-power continuous wave laser

Spectral beam combining technique is a simple and straightforward method to obtain a high-power laser beam. The beam combining system typically consists of three parts: fiber laser array, transform optical system and diffraction grating. Performance of the system (diffraction efficiency and laser induced damage threshold) is mainly determined by the diffraction grating. This paper describes a multilayer dielectric diffraction gating with high diffraction efficiency and low laser-induced damage threshold, which can be potentially used to obtain a high-power laser by combing laser beams. The diffraction grating is designed by coupled-wave analysis, and single-beam laser interference lithography is used to fabricate diffraction gratings. To verify the optical and thermal characteristics of the beam, we measure diffraction efficiency and the threshold for laser-induced damage. Finite element method simulation accurately represented temperature distribution in the grating during laser irradiation. This work provides integrated methods that include design of multilayer dielectric gratings, thermal analysis and device characterization using high-power laser.