Study On The Processing Quality Of Two Photon Polymerization Induced By Femtosecond Laser

Two-photon polymerization(TPP) induced by femtosecond laser is a powerful and potential technology to fabricate arbitrary three-dimensional(3D) micro/nanostructures of various materials such as polymers, hybrid materials, organically modified ceramics, and metals with subdiffaction-limit resolution(down to 100 nm). And it has been applied to microoptics, electronics, communications, biomedicine, microfluidic devices, MEMS and metamaterials. The processing quality of TPP is related to the performance of 3D micro/nanostructures, such as surface roughness has a great influence on the optical performance of microoptics devices. The factors affecting the processing quality of TPP include the principle errors of TPP(discretization error of the STL model and the step effect), the process parameters(laser power, exposure time, the numerical aperture of the objective, overlap rate of voxels and layer thickness), geometric errors of 3D scanning system and the deformation during the development phase. With the growing demand of large-area 3D micro/nanostructures, scanning system based on long-travel air bearing stage and two-dimensional(2D) galvanometer is gradually used. Compared with piezoelectric stage, geometric errors of three-axis air-bearing stage and 2D galvanometer will cause a large deviation of voxel’s position and posture in the coordinate system of specimen, which has great influences on the processing quality of TPP. So in this paper, the influences of processing parameters of TPP, geometric errors of three-axis air-bearing stage and 2D galvanometer on the processing quality are studied. The achievements are summarized as follows:a). TPP processing system based on 3D piezoelectric stage and 2D galvanometer was set up, including hardware(light source, optical components and the scanning system) and software(generation of processing data). The expression of resolution of TPP was deduced according to the free radical concentration model. It was found that the voxels were growing large and slender with the increase of laser power, exposure time and the decrease of numerical aperture of objective through theoretical analysis and physical experiment. When use smaller voxels, larger overlap rate and smaller layer thickness, we can obtain the micro-nano structures with better surface quality.b). The error model of three-axis air-bearing stage was established based on the multi-body system theory. And a global sensitivity analysis method based on variance was used to analyse the sensitivity of each error component. The results show that the angle errors of each axis have larger influences on voxel’s position than linear errors. The influence of X axis is larger than Y axis and Z axis and the influence of Y axis is larger than Z axis. In addition, three perpendicularity errors also have big influences on voxels’ position. The pitch, roll errors and straightness errors between X axis and Z axis and that between Y axis and Z axis have larger influences on voxels’ posture than other errors. After analysis of the influences of sensitive errors and total errors on voxel’s position and posture, a sphere was fabricated to analyze the effect of total errors on the processing quality of TPP. The geometric errors of air-bearing stage can cause the separation of voxels and affect the processing quality of 3D micro-nano structures.c). The relationship between the voxel’s position, posture and the angles of 2D galvanometer was deduced using the vector method. The error model was established when considering the geometric errors of the galvanometer scanning system and a global sensitivity analysis method based on variance was used to analyse the sensitivity of each error component. The results show that six angle errors have larger influences on voxel’s position and six angle errors of X scanner have larger influences on voxel’s posture. The influences of the three angles of X galvanometer on voxel’s posture is larger. After analysis of the influences of sensitive errors and total errors on voxel’s position and posture, a plane was fabricated to analyze the effect of total errors on the processing quality of TPP. Due to the effect of geometric errors, the actual surface quality is poorer than ideal surface quality.