Three Dimensional Confocal Imaging Based On Beam Scanning Technology

Confocal microscopy is a kind of 3D optical imaging technique which has been widely used in biomedical and material fields. Compared with the conventional microscopy, the decisive design feature of laser scanning confocal microscopy (LSCM) is the confocal pinhole arranged in a plane conjugate to the intermediate plane, and the object plane. As a result, the detector can only detect light that has passed the pinhole and get the information of a point at one time. In order to obtain the 3D information of the specimen, it must be collected point by point in the specimen and displayed by corresponding imaging points. Therefor, the scanning speed of illuminating point source determines the measurement efficiency of confocal 3D imaging.This paper titled"Three Dimensional Confocal Imaging Based On Beam Scanning Technology"utilizes beam scanning technique to achieve fast 3D imaging based on confocal microscopy. The oscillating mirrors were used to realize lateral beam scanning, which is the key work in this project. The detect objective lens was applied to step axially and then achieve axial beam scanning. The cooperation between lateral and axial beam scanning can realize 3D confocal imaging. The experimental system was designed and setted up based on the analysis of the 3D beam scanning technique, and utilized to imaging specimen in a high measurement efficiency.Five aspects in theoretical analysis and experiments have been completed as the main tasks.The first was to complete the theoritic analysis of edge criterion of stage specimen featured with limited height. Three dimensional point spread function of thin lens and the reflecting confocal imaging mode were used to deduct the edge criterion. Since the theoretical analysis model is more similar to the practical case, the analysis result could be used as the edge position criterion in the measurement of limited height stage specimen.The next content was to design the scanning model based on the oscillating mirror optical system and PZT stage. In the lateral direction, two oscillating mirrors driven by galvanometer motors were used to realize fast beam scanning. The two mirrors, whose axes were perpendicular to each other, were used to scan the illuminating point source in two directions simultaneously and they were located in close proximity to one another. In the axial direction, a piezoelectric actuator (PZT) stage was used to move the objective lens axially step by step. This beam scanning system could produce the fast and slow scan motions along the Y and X axes necessary to form a complete two-dimensional image, and cooperating with the axial stepping of the PZT thus a 3D scanning can be obtained. This beam scanning system could improve the 3D imaging speed significantly. Further, the reconstructing principle and the scanning error based on the use of oscillating mirrors were deeply analyzed. Relationship between the coordinates in the object space and the scanning angle of the oscillating mirror has been established based on the Geometrical Optics theory. The repeatability, linearity and stability of the oscillating mirror were analyzed according to its position feedback signal.In addition, the control software of the 3D imaging system was written using LabVIEW programming software. System software was designed to control the muti function data acquire device to generate analog signals to drive the oscillating mirrors and acquire the detection signals from the optical system at the same time. The 3D shape rescontraction software was used to process the acquired data and show the 3D measurement result of the specimen.Finally, a confocal microscopy system using the designed beam scanning model was setted up. The 3D measurement result of standard resolution board demonstrated the correctness of the reconstructing principle. Then, several typical specimen featured with micro-structure were measured by this system, and the results were given at last. Besides, the measurement time of all measurements (600 points×100 lines×100 planes) can be limited in 300 seconds, thus this confocal microscopy system is good at imaging efficiency.