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多层电介质反射式衍射光栅作为光谱合成系统的核心元件,在高功率激光辐照下的表面形变将导致其衍射特性改变,进而影响系统合成光束质量和衍射效率。搭建泰曼-格林干涉仪探测在高功率激光辐照下衍射光栅表面的干涉条纹,经图像处理及泽尼克多项式拟合实现光栅表面形貌的重建。采用高功率光纤激光辐照加热光栅,测量另一光束经过热畸变光栅后的光束质量和衍射效率演变。结果表明,在高功率激光辐照下光栅表面形变高度分布为高斯型,辐照功率密度3kW/cm~2时,干涉条纹对应区域内的光栅表面在垂直方向上隆起,最大高度为127nm。表面形变引起衍射光束质量因子M2退化,这种退化主要来自衍射光远场发散角的增大。光栅衍射效率波动幅度小于1.8%。
Multilayer dielectric reflective diffraction grating, as the core component of the optical system, changes its diffraction properties under the high-power laser irradiation, which will affect the quality of the synthesized laser beam and the diffraction efficiency. The interference fringes on the surface of the diffraction grating under high-power laser irradiation were detected by using the Terman-Green interferometer. The reconstruction of the grating surface topography was achieved by image processing and Zernike polynomial fitting. The high-power fiber laser is used to irradiate the heating grating to measure the beam quality and the diffraction efficiency of the other beam after the thermal distortion grating. The results show that the gratings in the area corresponding to the interference fringes rise in the vertical direction and the maximum height is 127nm when the grating surface deformation height distribution is Gaussian at high power laser irradiation and the irradiation power density is 3kW / cm ~ 2. Deformation of the diffracted beam causes degradation of the quality factor M2 of the diffracted beam, which is mainly due to the increase of the divergence angle of the far-field of the diffracted light. Grating diffraction efficiency fluctuations of less than 1.8%.