Research On Material Removal Of YAG Crystal During Lapping And Polishing

The laser,a key device of national defense,industry and medical fields,is used more widely and its performance improves continuously.The laser crystal is the main working medium of the laser,and its properties and processing quality determine the performance and the service life of the laser.How to process the laser crystal with high efficiency and high quality has become a critical problem to be urgently solved in the laser manufacturing technology.Yttrium aluminum garnet?YAG?has fine optical properties,stably physical and chemical properties,easy doping and other advantages,and it has been one of the most promising laser crystal material.At present,some studies on processing technology of YAG has been carried out,but it's still difficult to obtain a non-damage surface.This paper analyzed the evolution of surface/subsurface damage in lapping and polishing,and explored the impact of pH value on material removal and surface quality.Based on the mechanism of scratches generation,scratches on the polished surface were controlled by optimizing process parameters,and an improved processing technology was proposed,consisted of cutting,lapping and chemical mechanical polishing.?1?The evolution of surface defects and subsurface damage was studied based on experiments and theoretical calculations.Al₂O₃ particles with different sizes were used to analyze the evolution of surface and subsurface damage and material removal mechanism of YAG.Compared the load of the single particle with the critical load of the median crack,the effect of particle size on the material removal mechanism was analyzed.Moreover,two models between SSD and the particle size,surface roughness were established respectively based on the indentation fracture mechanics.?2?The effect of pH value of the polishing slurry on the chemical reaction and material removal mechanism was analyzed.The value of material removal rate?MRR?under acidic conditions is about three times the value under alkaline conditions,while the surface roughness has no significant change.The chemical reaction mechanism was analyzed under different conditions and proposed a material removal model based on atomic extraction.The mechanical actions were explained by the analysis of particle size,zeta potential and coefficient of friction.Different material removal mechanism and the more particles involved in polishing resulted in a higher MRR under acidic conditions.?3?The generation mechanisms and control method of scratches with a sub-nanometer depth post CMP were proposed.In order to obtain a non-damaged polished surface,the generation mechanisms of scratches were summarized,and the effect of processing parameters and polishing pad on scratches were studied.In addition,a process with a higher speed and lower pressure was proposed.?4?Based on the evolution of surface/subsurface damage and MRR,particle size was chosen reasonably and processing technology was optimized.The processing technology of this paper can achieve a non-damage surface efficiently,and the roughness Sa is 0.08 nm,which has great value to guide the actual production of YAG single crystal.