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题名	多层电介质反射式光栅的热光效应研究
作者	公维超
文献子类	硕士
导师	何兵
关键词	光谱合成 Spectral beam combining 多层电介质光栅 Multilayer dielectric grating 光栅热效应 Grating thermal effects 泰曼-格林干涉仪 Twyman-Green interferometer 衍射特性 Diffraction characteristic
其他题名	Research on thermo-optic effect of multilayer dielectric reflection grating
英文摘要	光谱合成基于色散的逆过程，利用衍射光栅等色散元件将不同波长和不同入射方向的子光束阵列进行共孔径合成，能获得高功率和高光束质量的激光，成为激光技术领域的研究热点之一。多层电介质光栅是光谱合成的核心元件，具有宽频谱，高衍射效率，高损伤阈值，偏振无关等特性，近年来在高功率光纤激光光谱合成系统中得到广泛应用。在高功率密度激光辐照下，多层电介质光栅产生的热效应会改变光栅的光学特性，严重时甚至会损坏光栅。因此，研究多层电介质光栅的热光效应对提高光谱合成的输出功率，改善合成光束质量具有重要意义。 本文研究多层电介质光栅在高功率密度激光辐照下的热效应及其对衍射特性的影响，分别进行了理论模拟和实验验证。文中实验基于自主研发的偏振无关宽谱多层电介质光栅。 使用有限元分析软件模拟多层电介质光栅在高功率激光辐照下因热效应产生的热畸变，包括光栅厚度对热畸变的影响和光栅不同部分的形变量。模拟表明，光栅因热效应出现表面热畸变，分布与辐照激光强度一致，主要来自于光栅基底的形变。实验上基于泰曼-格林干涉仪搭建光栅表面形变测量系统，红外热像仪获得光栅温度，干涉仪获得光栅表面的干涉条纹图像。通过对条纹图像进行数字图像处理和泽尼克多项式拟合，得到光栅表面形变的精确分布。实验表明，在高功率激光辐照下，光栅表面形变为高斯分布，与辐照激光强度一致。当辐照功率密度3.6 kW/cm2时，最大形变高度为140.4 nm。 基于光栅热畸变的研究结果计算其引入的近场相位调制，然后根据标量衍射理论计算调制后的衍射光远场强度分布和光束质量。模拟结果表明，光栅热畸变会改变衍射光远场强度分布，从而引起光束质量退化。搭建研究光栅热畸变对衍射特性影响的实验平台，以高功率激光辐照光栅，测量另一束光经热畸变光栅衍射后的远场光斑、光束质量M2和衍射效率。实验表明，光栅热畸变使衍射光远场强度分布变为非高斯型，中心能量降低，旁瓣能量增加，最终导致衍射光光束质量退化。光栅衍射效率下降幅度小于1.8%。; Spectral beam combining (SBC) combines sub-beams at different wavelength into single aperture output to obtain high power and high beam quality laser by dispersive element such as diffraction grating. Therefor it has become one of the research hotspot in the field of high-energy laser. Multilayer dielectric grating (MDG) is characterized of large bandwidth, high diffraction efficiency and damage threshold and polarization independence. In recent years, it has been applied in high power fiber laser SBC system. As the core element in SBC, the thermal effect of the grating under high laser power density will have a significant impact range from a change of the optical characteristics to damage of grating. Research on thermo-optic effect of multilayer dielectric grating will be of great significance to increase output power of spectral beam combining and improve beam quality. In this paper, the thermal effect and its influence on diffraction characteristic of MDG under high power density laser irradiation is studied. The theoretical simulation and experimental verification are carried out respectively. The experiment is based on self-developed MDG characterized of polarization independence and large bandwidth. The thermal distortion caused by the thermal effect of MDG under high power laser irradiation is simulated by COMSOL software, including the influence of thickness of the grating on thermal distortion and the deformation of different parts of the grating. The result indicates the surface deformation appears and the deformation distribution is consistent with the intensity of irradiated laser, which mostly caused by the deformation of grating substrate. Based on Twyman-Green interferometer, the grating surface deformation measurement system is built. An infrared thermal camera measures the temperature of the grating and the interferometer obtains the interference fringe of grating surface. The precise distribution of grating surface deformation is reconstructed by digital image processing and Zernike polynomial fitting of the fringe image. The experimental results show that the surface deformation is Gaussian distribution consistent with the intensity of the irradiated high power laser. When the irradiation power density is 3.6 kW/cm2, the maximum deformation height is 140.4 nm. The near-field phase modulation is calculated by the result of grating thermal distortion and then the far-field intensity distribution and beam quality of diffracted light is also calculated according to the scalar diffraction theory. The simulation shows the grating thermal distortion will change the intensity distribution of diffracted light and cause the degradation of beam quality. The experimental system to research the influence of thermal distortion on grating diffraction characteristics is built. The grating is irradiated by one high power fiber laser and the far-field spot, beam quality M2, and efficiency of another diffracted light are measured. The result indicates that the grating thermal distortion causes the far-field intensity distribution of diffracted light to become non-Gaussian distribution, which eventually results in degradation of the beam quality of diffracted light. The diffraction efficiency decreases by less than 1.8%.
学科主题	光学工程
内容类型	学位论文
源URL	[http://ir.siom.ac.cn/handle/181231/30990]
专题	中国科学院上海光学精密机械研究所
作者单位	中国科学院上海光学精密机械研究所
推荐引用方式 GB/T 7714	公维超. 多层电介质反射式光栅的热光效应研究[D].

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