Theory And Simulation Of Femtosecond Laser Two-photon Polymerizatiom Processing Based On Optical Tweezers

With the appearance of femtosecond laser,ultra-short pulse laser processing technology has developed rapidly.Compared with long pulsed laser,femtosecond pulsed laser havs unique advantages such as small thermal effect and small area of action,making ultra-short pulsed laser technology a hot research topic.At the same time,the femtosecond laser two-photon polymerization process stands out from many micro-nano processing processes due to its advantages such as rapid forming,high processing resolution,and ability to realize three-dimensional processing,and is attracting more and more attention from scholars.This article first introduced the advantages and applications of femtosecond lasers,summarized the current status of femtosecond laser two-photon photopolymer processing,and presented the basic principles of femtosecond laser-material interaction and two-photon polymerization processing.The scheme adopted by scholars to improve the resolution of femtosecond laser two-photon polymerization processing.Then,according to the basic theory of two-photon absorption and two-photon photopolymerization in the process of two-photon polymerization of femtosecond lasers,based on the theory of free radical concentration fluctuation and the theory of an aperture gather effect,the line width formula of femtosecond laser two-photon polymerization single-scanning processing was proposed.The effect of each parameter including the numerical aperture of the objective lens and the two-photon absorption cross section are analyzed.Mainly disscuss the effect of femtosecond laser power and beam scanning speed on the line width.Compared with the original two-photon polymerization processing line width formula and the experimental results in the literature,it is proved that in the theoretical analysis of two-photon polymerization processing line width,the effect of femtosecond optical tweezers must be considered.Then based on the single-pass scanning process of two-photon polymerization,a new method for multiple fast scanning of femtosecond laser two-photonpolymerization was proposed.Based on the general formula of a single scan,combined with the effect of the theory of femtosecond aperture convergence on the line width,a general formula for the line width of multiple rapid scans was deduced.The effect of various parameters on the processing line width during multiple rapid scans was analyzed.The influence of the new parameter scan interval time on the line width of multiple scans relative to single scan was analyzed.Comprehensively expounded the advantages of rapid multiple scans compared to single scan,providing a theoretical basis for posterity to adopt multiple rapid scan methods to process smaller linewidths.Finally,COMSOL Mutiphysics was used to simulate the various aspects involved in the two-photon polymerization process.The parameters setted in the software,the free radical release mechanism,the forces on the free radicals during the whole process,the free radicals photopolymerization reaction and the problem of solidified lines are introduced.Comparing the line widths of the solidified lines obtained by COMSOL simulation with the line widths calculated theoretically,they are basically consistent,and try to process some specific micro/nano structure.