Co < Sub > 2 < / Sub > Laser Damage Repair Of Fused Quartz

In the high power laser systems,the optical element’s laser damages are very important question needed to be solved first. The fused silica tends to be damaged induced by the defects under irradiation of high power laser. Once the damage initiates, it will grow exponentially with the additional pulses. The CO2laser mitigation for the laser damage on the fused silica can increase the lifetime of optical element and lower the cost.In this thesis,CO2laser mitigation for the fused silica’s laser damage is the main research object. The theoretical and experimental studies have systematicly been conducted. The damage mechanism and mitigation mechanism are deep analyzed. The correlations between laser parameters and mitigation morphology, and damage resistance of fused silica optics are investigated. The mitigation technique is optimized and the mitigation protocol and procedure are established. The important results are summarized as follows:Theoretical results:1.The development of CO2laser mitigation in domestic and foreign are reviewed,including the thermal properties of fused silica,damage mechanism,damage growth and mitigation mechanism.The enhanced optical strength of mitigated spots is mainly attributed to the healing of microcracks in the surrounding material.2.The main problem includes:bubbles,ablation and stress.These problems will reduce the damage threshold.Optimizing the mitigation technique can solve those problems.3.The mitigation can be classified as three ways in terms of scanning methods, point scanning,raster scanning and galvanometer scanning.Each method has its advantages and disadvantages,and fit for different damage sites.Experimental results:1.The point scanning and galvanometer scanning are experimental studied,including HF etching,damage site fabrication,damage threshold test,laser mitigation and annealing. 2.The effects of laser parameters on mitigation are investigated,including laser power,mitigation time,spot size,laser ablation.The diameter of spot size of point scanning is2～2.5mm.Laser power is14～16W.Mitigation time is3～5s.If the spot size is larger,the effected area of is larger.And with the increasing laser power and mitigation time,the depth of mitigation site is growing.The spot size of galvanometer scanning laser beam is100μm.And when the duty cycle grows,the mitigation area and depth grow too.When the scanning speed grows, the mitigation area and depth decrease.3. The advantages and disadvantages of two methods are compared.The point scanning is fit for the damage size under200μm.The galvanometer scanning is fit for the damage size above200μm.