A Research On Self-focused Beam Array Applied To High-throughput Laser Surface Treatment

The femtosecond laser can produce high-precision and high-resolution microstructures or nanostructures on the surface of the material and these surface structures can significantly change the surface properties of materials,such as light trapping ability and hydrophilicity,etc.,and have extremely important application values.For example,the black silicon absorbing layer on the surface of widely used silicon-based photovoltaic cells relies on these surface nano-or micro-scale structures,so that incident light undergoes multiple scattering,and the absorption rate increases from 60% to more than 90% on the surface of ordinary silicon.However,the commonly used serial femtosecond laser surface treatment usually focuses a single laser beam on the surface of a silicon sample and simultaneously performs a two-dimensional scan of the laser focal position for a long time to process a large area of the sample.Most of the laser energy is wasted and the processing efficiency is extremely low.Therefore,it is of great research value and significance to study the parallel method suitable for high-throughput laser surface treatment.This paper presents a self-focued beam array method for high-throughput laser surface treatment,and proves the rationality of the method through experiments and theoretical simulations,which is different from the more expensive optical devices such as the use of micro-lens arrays and diffractive optical elements in traditional parallel processing methods.Only a common quartz glass optical element is needed,and the multi-beam interference principle and nonlinear Kerr effect are flexibly and cleverly combined.The main research contents include:(1)The principle of self-focusing beam array applied to high-throughput laser surface treatment is introduced.The principle combines third-order nonlinear effects and multi-beam interference technology.The influence of parameters such as the initial phase of incident light and the incident angle of light intensity on the interference pattern is analyzed,and the self-focusing effect caused by the third-order nonlinear effect is analyzed.(2)The three-dimensional non-axisymmetric propagation equation of the self-focusing beam array is established.After scanning and screening the initial parameters such as incident angle and glass thickness,the optimal simulation parameters are obtained and the final simulation results are obtained.Simulation results confirm that the self-focused beam array interferes on the glass surface first,and then experienced nonlinear self-focusing in the glass.The wavefront is still the converging wavefront when it exited from the glass.The interference array continues to focus in the glass until it starts to diverge after reaching the focal plane in the air..(3)After the simulation of the self-focusing beam array,combined with the optimal simulation parameters,an experimental system was built to verify the experiment.First we built a 4f imaging system to image the entire propagation process,the imaging results are basically the same as the simulation results;then the black silicon ablation experiment was carried out at the focal plane in the air,a single processing can get a 1.8mm long processing area,the efficiency is greatly improved.