微球透镜对亚波长表面结构的显微成像研究

为了研究微球透镜对亚波长物体的成像特性,利用直径为3.4μm的二氧化硅微球透镜对刻录蓝光光碟的亚波长表面结构进行了显微成像实验,观察了不同排列方式和液体浸没深度下微球透镜的成像特性。实验结果表明:微球透镜在不同浸没深度下对亚波长表面结构具有放大作用,放大率为1.2~1.8倍,并且通过微球透镜的密排列,可以获得更大的视场;浸没液体深度增大时,图像的放大率减小,视场增大。基于时域有限差分的电场仿真表明,微球透镜可以将光场汇聚成半高全宽为260nm,纵向可持续几个微米的高强度光区域,引起强的背景散射,从而获得普通光学显微镜不能分辨的亚波长表面结构图像。

Microscopic imaging of sub-wavelength surface pattern based on microsphere lenses

For the study of the sub-wavelength microscopic imaging properties of microsphere lenses, the Silica microsphere lenses with a diameter 3.4μm are used to image the sub-wavelength surface structure of data-recorded Blu-ray disc. The imaging properties of the microsphere with different arrangements and immersed depths are observed. The experimental results show that the sub-wavelength surface patterns can be magnified by the microsphere lens with different immersed depths, and the magnification is about 1.2~1.8. A larger field of view can be obtained by the closely packed microsphere lenses. When the depth of the immersed medium increases, the magnification decreases and the field of view increases. The simulation of electric filed distribution based on the FDTD method illuminates that the microsphere can form a focus with high intensity, which has a full width of half maximum about 260 nm and can maintain several microns in the longitudinal direction. The focus can result in strange back-scattering effect and the sub-wavelength surface structures which cannot be resolved by conventional optical microscope can be captured by the microsphere lenses.