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为了提高激光直写加工衍射光学元件时的线条质量,提出一种离焦激光直写的线宽稳定方法。该方法通过同时调节激光功率和离焦量,使光刻胶的曝光阈值处于线宽对曝光量的变化率较小位置,从而可以弱化线宽对实际曝光量或光刻胶阈值等变化的敏感度,提高利用离焦方法进行衍射光学元件制作时的线宽稳定性。推导了稳定线宽后的光功率控制模型和线宽模型,模型中的变量仅为离焦量,降低了光功率控制的复杂性。利用632.8 nm的He-Ne激光和NA=0.1的物镜在CCD上对采用该方法后的离焦线宽模型进行验证,实验结果与理论模型吻合较好。该方法对于线宽稳定度较高的衍射光学元件制作具有重要价值。
In order to improve the line quality of laser direct writing diffraction optical element, a method of line width stabilization of direct laser writing of defocus is proposed. By adjusting the laser power and the amount of defocus at the same time, the method exposes the exposure threshold of the photoresist to a position where the change rate of the line width to the exposure amount is small, thereby weakening the sensitivity of the line width to changes in the actual exposure or the photoresist threshold Degree, improve the use of defocus method diffractive optical element fabrication line width stability. The optical power control model and the linewidth model after the stable linewidth are derived. The variables in the model are only the defocus amount, which reduces the complexity of the optical power control. Using the 632.8 nm He-Ne laser and NA = 0.1 objective lens on the CCD to verify the use of the method of the defocused linewidth model to verify the experimental results agree well with the theoretical model. The method is of great value to the manufacture of diffractive optical elements with high line width stability.