金属材料薄膜的光学常数会随膜层厚度发生变化，从而导致薄膜的光谱特性也发生变化。在制备工艺中，不论是热蒸发工艺还是溅射工艺，Ni80Cr20（简称镍铬）薄膜在较“薄”和较“厚”的时候光谱中性度都较差，并且其光谱特性趋势相反。理论计算结果表明，增加镍铬合金中Cr（铬）的比份可以提高“薄”膜的中性度，而“厚”膜则需要提高Ni（镍）的比份。针对光谱特性相反的“薄”膜和“厚”膜，分别提出了“有意分馏”和增加镍的比例的方法来改善光谱的中性度。试验结果表明：为改善膜层的中性度，低密度时可采用“有意分馏”的热蒸发工艺来提高膜层中铬的含量；而高密度时则可以镀制纯镍。“有意分馏”的热蒸发工艺可将光谱中性度提升至1.8%；纯镍工艺可将OD4的光谱中性度提升至4.6%。所提出的改进的镀膜工艺是有效的，并为光谱检测、光纤通讯、摄影摄像等应用领域的衰减片制备工艺的改进提供了参考。

The optical properties of metallic materials change with the thickness of the film thickness, resulting in the change of their spectral characteristics. If the film is deposited by thermal evaporation or sputtering, the neutrality of Ni80Cr20 film is poor when the thickness is too thin or thick. The theoretical calculation results show that increasing the proportion of chromium in Ni-Cr alloy can improve the neutrality of the thin film, while the proportion of nickel needs to be increased for the thick film. As for the opposite spectral characteristics of the thin and thick films, intentional fractionation and increasing the proportion of Ni are proposed to improve the spectral neutrality, respectively. The test result shows that the improved coating process is effective.