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数值孔径N·A是物镜主要的特性指标,长期被解释为是表征物镜集光能力的参数。数值孔径愈大,物镜集光能力就愈强,其分辨率就愈高。由于N·A=nsinα(n为介质折射率;α为物镜孔径半角),故提高物镜集光能力有两条途径,其一是扩大物镜孔径角,其二是提高介质折射率。这第二条途径就是采用油镜。而油镜何以能提高集光能力呢?许多文献常用图1方法比较油镜与干镜的集光能力。文献认为,由于油折射率比空气大,使从试样上反射的、倾斜度较大的、原来不能进入镜头的反射光,如R_2,也能进入镜头。这实际是说,由于油介质作用,从试样反射的光
The numerical aperture N · A is the main characteristic index of the objective lens and has long been interpreted as a parameter that characterizes the objective optical power. The larger the numerical aperture is, the stronger the objective collecting ability is and the higher the resolution is. Because N · A = nsinα (n is the refractive index of the medium; α is the half angle of the objective lens aperture), there are two ways to improve the light collecting capability of the objective lens. One is to enlarge the aperture angle of the objective lens and the other is to increase the medium refractive index. This second approach is to use oil mirror. How can the oil mirror to improve light gathering ability? Many documents often use Figure 1 method to compare the light collection lens and dry mirror ability. The literature suggests that since the refractive index of the oil is larger than the air, the reflected light from the sample, which has a large inclination and can not enter the lens, can also enter the lens. This is actually saying that light is reflected from the sample due to the oil medium effect