Research on Focusing Method of High Numerical Aperture Objective Lens in Tip-enhanced Raman System
SUN Xiao-shuang1,GAO Si-tian1,HUANG Lu1,ZHU Min-hao2,LIU Lin-wei2
1. National Institute of Metrology, Beijing 100029, China
2. College of Metrology & Measurement Engineering, China Jiliang University, Hangzhou, Zhejiang 310018, China
Abstract：In order to improve the focusing accuracy and efficiency of tip-enhanced Raman system(TERS), an automatic focusing method is proposed by analyzing the pixel value of the spot image captured by CCD camera.Fast coarse focusing to narrow the focusing range, and then slow fine focusing to improve the focusing accuracy.The experimental results show that, compared with Tenengrad evaluation function, the variance evaluation function is more suitable for automatic focusing of tip-enhanced Raman system.When focusing on the sample surface, the unbiased estimation variance of focusing result is less than 0.25 μm, which has high repeatability and robustness.Fast coarse focusing can improve the focusing efficiency and avoid falling into the local optimal solution.The curve of slow fine focusing evaluation function presents an “M” shape near the focus, which can be adjusted by quadratic fitting to improve the focusing accuracy.
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2022, Vol. 43 
