Miniaturized confocal Raman microscopy based on MEMS mirror scanning

Abstract

Confocal Raman microscopy can provide molecular distribution and three-dimensional topographic information of the substances, and is widely used in biomedical, material chemistry and physical science fields. However, in the traditional confocal Raman microscopes, the devices have large size, and scan lens and tube lens need conjugate placement taking up a lot of space, these make it difficult to reduce the size of the system. In order to solve the mentioned problems, we propose a scanning mechanism based on MEMS scanning mirror without scan lens and tube lens, and develop a miniature confocal Raman microscope base on this mechanism. In which the MEMS scanning mirror is used for lateral two-dimensional scanning of the laser beam, and an aspherical lens is placed directly behind the MEMS scanning mirror as the objective, as well as the MEMS mirror is positioned at the back focal plane of the aspherical lens to obtain a better spatial resolution. Compared with the traditional confocal Raman microscope based on galvanometer scanning, a miniaturized MEMS scanning mirror is used in our system, and scan lens and tube lens are omitted, which greatly reduces the size of this system. Meanwhile, the reduction of optical components and the shortening of the optical length improve the signal detection efficiency, which is very beneficial for the detection of relatively weak Raman spectral signals. The preliminary experimental results demonstrate the system lateral resolution and axial resolution are about 0.8 μm and 5.5 μm, respectively, and the Raman spectral resolution is 0.2 nm, which is basically consistent with the theoretical analysis.