Constant exposure dose control for laser direct writing of mesh in a deep concave spherical substrate

For the purpose of fabricating high-quality mesh in a deep concave spherical substrate by laser direct writing technique, the constant exposure dose control must be realized during the whole scanning process. Firstly, the principle of the equipment for fabricating mesh in a deep concave spherical substrate via laser direct writing technique was introduced. Then scanning motion states for writing arbitrary line of latitude were analyzed, and the formulas that expresses the mathematical relationships between the dimensions of the substrate, parameters of mesh and the scanning velocity were deduced. The mathematical model of scanning with constant exposure dose was built, and the servo control system including software and hardware was developed according to the mathematical model. The servo control system could tune the scanning angular velocity precisely according to the latitude of lines to maintain the linear velocity invariantly, so as to keep the exposure dose constant and improve the quality of lines. So far, constant exposure dose control was realized finally. Mesh with 500 m gridding period was fabricated in a deep concave spherical substrate with a rise-span ratio of 0.31. Lines on the substrate have good uniformity, steep and straight side walls parallel to each other after development, and errors of line width and gridding period are within 1% and 5%, respectively.