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衍射光学元件被广泛应用于激光光束整形领域中。然而,在实际测量中常常发现衍射效率实际的测量值与设计值存在较大的偏差,原因之一在于输出的焦斑主瓣以外会产生高级次衍射杂散光。文中从理论上推导了高级次衍射杂散光产生的原因并对具有不同设计参数的衍射光学元件进行了仿真分析。通过研究,定义了一个新的参数,相对周期。它与光波波长成正比,与衍射光学元件的采样单元尺寸以及远场衍射角成反比。结果表明,衍射光学元件的衍射效率只是关于相对周期的函数,而与焦斑主瓣的具体形状无关。随着相对周期的增加,衍射效率随之增大。所以可通过适当选取远场衍射角和采样单元尺寸的参数以调整相对周期的大小,有效抑制高级次衍射杂散光。该参数在衍射元件的设计中具有重要的指导意义。
Diffractive optical elements are widely used in the field of laser beam shaping. However, it is often found that the actual measured value of the diffraction efficiency deviates from the designed value greatly in practical measurement. One of the reasons is that high-order diffracted stray light is generated beyond the main lobe of the output focal spot. In this paper, the reason of high-order diffraction stray light is deduced theoretically and the diffraction optical elements with different design parameters are simulated. Through research, a new parameter is defined, relative period. It is proportional to the wavelength of the light wave and inversely proportional to the size of the sample cell of the diffractive optical element and the far-field diffraction angle. The results show that the diffraction efficiency of the diffractive optical element is only a function of the relative period, irrespective of the specific shape of the main lobe of the focal spot. As the relative period increases, the diffraction efficiency increases. Therefore, the parameters of the far-field diffraction angle and the sampling unit size can be appropriately selected to adjust the relative cycle size and effectively suppress the high-order diffraction stray light. This parameter has important guiding significance in the design of diffraction element.