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摘要： 理论计算了Ni、Cr和Ni80Cr20三种材料的光学特性，确定了镍铬成份变化对Ni80Cr20的影响。在高低两个真空度条件下采用电子枪蒸发工艺进行了Ni80Cr20的镀膜实验，结果表明，低真空度时“薄”膜的中性度较好，而高真空度时“厚”膜中性度较好。采用X射线能谱分析发现“薄”膜铬含量高于膜料，而“厚”膜更高，高真空度薄膜略有氧化，而低真空度氧化更严重。从残余气体和蒸发方式方面分析了镍铬成份差异的原因，再结合氧化对薄膜特性的影响，确定了不同真空度薄膜中性度差异的原因。

关键词：

中性密度滤光片； 中性度； 镍铬合金； 电子槍； 蒸发； 分馏

中图分类号： O 484.1文献标志码： Adoi： 10.3969/j.issn.10055630.2017.01.011

The influence of vacuum on neutrality of Ni80Cr20 filter

ZHANG Yongxi， JIN Xiu， YANG Wenhua， ZHANG Yanshu， REN Shaopeng，

WANG Ruisheng， HU Wenwen， YANG Xiaoyu

（Shenyang Academy of Instrumentation Science Co.，Ltd.， Shenyang 110043， China）

Abstract：

The optical characteristics of Ni，Cr and Ni80Cr20 were calculated in theory to determine the impact on Ni80Cr20 when changing the proportions of nickel and chromium.Electron gun evaporation experiments were carried out separately at high vacuum and low vacuum conditions.The results showed that the "thin" film had better neutrality when coated at low vacuum，while the "thick" film had better neutrality when coated at high vacuum.Xray spectroscopy analysis found that the "thin" film had a little more chromium and the "thick" film even had much more chromium than the amount in coating material.Furthermore，the film is slightly oxidized at high vacuum and even severely at low vacuum condition.The influence in the compositions of nickel and chromium in the film by residual gas and evaporation way was analyzed.The influence over the optical characteristics by oxidation was discussed.The reason for different neutrality of films coated at different vacuum was found.

Keywords： neutral density optical filters； neutrality； nickelchromium alloy； electron gun； evaporation； fractionation

引言

中性密度滤光片是一种起光能衰减作用的光学元件，这种衰减作用在一定程度上是非选择性的。中性密度滤光片对不同波长光线的衰减能力大致相同，只起到减弱光线的作用，而对原物体的颜色不会产生任何影响，可以真实再现景物的色差，因而在摄影领域被用作减光镜，在其他光学系统中则用于多波段减光，或者用于系统定标。

中性密度滤光片的生产方式很多，最常用的是在玻璃基底上镀制单层镍、铬或镍铬合金膜[13] 。镍铬合金的种类较多，但常用的是Ni80Cr20。然而，由于合金材料蒸发时存在分馏现象，所以采用热蒸发工艺镀制Ni80Cr20时工艺稳定性和重复性较差，蒸镀条件对薄膜的中性度有很大影响。本文从实验出发，研究了真空度对电子束蒸发Ni80Cr20膜中性度的影响。……