Laser Polishing Mechanism And Process Study On KDP Crystals

As a kind of excellent optical crystal,KDP(Potassium Dihydrogen Phosphate)has good nonlinear optical properties and high laser induced damage threshold,and is widely used in nonlinear optical fields.However,KDP crystal has a series of unfavo rable physical properties when optical processing such as,soft brittle,easy deliquescence,heat sensitive and anisotropy,which bring a lot of difficulties for high precision machining.In order to explore a new precision machining method of KDP crystal,this research put forward an innovative method that polishing KDP crystals by laser.The feasibility of this method to improving the surface quality of KDP crystal was discussed in various aspects,such as the interaction mechanism between laser and KDP c rystal,polishing device,process parameters,laser beam and so on.Firstly,four polishing solutions were put forward and verified respectively to obtain the most effective polishing solution.Secondly,each factor of surface polished quality of KDP crystal was studied to elucidate the influence of process parameters,such as wavelength,incident angle,energy density of single pulse,overlapping rate,way of scanning,etc.Thirdly,the laser polishing parameters were optimized to improve the surface roughness of KDP crystal.Finally,a deep study was made to discuss the interaction mechanism between laser and KDP crystal.The achievements acquired in this research mainly include the following aspects:(1)The most effective polishing solution was obtained,which the galvanometer was linear scanning and the workpiece was linear motion.And a most ideal polishing deveice was also put forward,which the laser rotate and the workpiece motion in a straight line.(2)The influence laws of key parameters on surface quality of polished KDP crystal were obtained and the process parameters were optimized.Under the conditions of picosecond laser wavelength of 355 nm,focal length f=56 mm,laser beam incident angle?=84°,laser repetition frequency f=800kHz,pulse energy density Q=2.4 J/cm~2,overlapping of light spot O=60%,multiple directions(45°)cross scanning and processing times T=10 times,the surface quality of KDP crystal were greatly improved and the roughness of the surface was reduced to about Ra=76 nm;(3)By analyzing the experiment results,the interaction mechanism between laser polishing parameters and KDP crystal were systematically discussed.