Femtosecond Laser Power Closed-loop Control System Based On Acousto-optic Modulation

Since the new century,with the development of science and technology,there has been a demand for ultra-fine and true three-dimensional structures such as micro-nano robots and hypermaterials in some fields.However,reductive manufacturing cannot cope with the manufacturing of such structures.Additive manufacturing technology,such as femtosecond laser two-photon polymerization 3D printing technology,has been successfully applied in the fields of micro-mechanical systems,micro-nano optical systems,biomedicine and so on,thanks to their high precision and maskless working characteristics.Since 2008,the research on deformable structures has shown a broader application prospect for two-photon polymerization 3D printing technology.Studies have shown that deformable structures can be fabricated by changing the laser power during the 3D printing process.However,the current methods to achieve variable power processing are step-by-step processing or openloop power modulation.Step-by-step processing increases the complexity of the manufacturing process and process,and reduces the processing efficiency.Open-loop power modulation without power closed-loop feedback mechanism can not guarantee the stability of long-term laser work,affecting the quality of the print structure.In order to solve the above problems,this paper designs a closed-loop control system of laser power based on acousto-optic modulation,which can be applied to the femtosecond laser two-photon aggregation 3D printing system.It is expected to achieve the function of variable power 3D printing system.The main work of this paper is as follows(1)For the lack of power stability control and low efficiency of manual adjustment,a closed-loop control system for laser power based on acousto-optic modulation is designed in this paper.The system can suppress the fluctuation of laser power and automatically adjust the power value according to the external trigger signal.(2)The closed-loop power control circuit board(hereinafter referred to as the “ power control card ”)is designed,and the PC software of the power control system and the microcontroller program based on PID(proportional integral derivative)algorithm are written.The power control card can be used with PC software and can run independently.It is expected to achieve universal functions between similar 3D printing systems.(3)The experimental optical path of the laser power closed-loop control system was built,and then the performance test of the closed-loop control system to suppress laser power fluctuation was carried out.The test results show that the system can suppress the maximum fluctuation of laser power at about 1 % and the standard deviation fluctuation at about 0.1 %.In addition,the response speed of the closed-loop control system was tested in the experiment,and it was determined that the maximum time required for the system to change power from beginning to power stability was 90 ms.Finally,aiming at the problems of poor low power control effect and inaccurate center power positioning found in the system test,the reasons are analyzed,and the solutions are put forward to improve the subsequent research work.In this paper,a laser power closed-loop control system based on acousto-optic modulation is designed.Combining the system with femtosecond laser two-photon polymerization 3D printing system,the function of automatic closed-loop power modulation in machining process can be realized.The combined 3D printing system is expected to achieve variable power and heterogeneous 3D printing,which broadens the way for the application of femtosecond laser two-photon polymerization 3D printing system in the field of deformable structure manufacturing.