Research On Directional Growth And Properties Of KDP/DKDP Crystals

Controllable fusion energy is regarded as one of the most promising methods for human being to resolve the problems and environment problems in the future,due to its safety and environment-friendly advantage.Inertial Confinement Fusion(ICF)driven by large size high power laser system is an efficient access for human being to gain fusion energy peaceful and safety,which attracts the world's attention.Large size high quality electro-optical crystal and frequency conversion crystal are important optical elements in the high power laser system for ICF.Throughout all the present nonlinear optical crystals,KDP crystal and its deuterium salt,(D)KDP crystal is the only one crystal which can meet the requirement of ICF research.Potassium dihydrogen phosphate(KH2PO4,or KDP)and its analogs deuterated potassium dihydrogen phosphate(K(HxD1-x)2PO4,or DKDP),is one of the most famous nonlinear optical crystals that people ever found and there have been more than 80 years for research on the KDP(DKDP)crystal growth.In the 50's of 20th century,KDP crystal used as a typical piezoelectric crystal,and was a kind of strategic materials used in manufacture of sonar,and as piezoelectric transducer material in daily life.Thus the demand for such crystals is considerable.In the early of 1960s,when the laser technique appeared,KDP was found with large nonlinear-optical coefficient,high laser damage threshold(LDT)and high transmittance from near infrared to ultraviolet.Thus,it can be used to make various laser frequency doublers.However,under the premise of meeting the requirements of CIF crystals,how improve the crystal utilization and crystal growth efficiency is our pursuit during we grow and machine(D)KDP crystals.Firstly,growth method of(D)KDP crystal is developing from the traditional temperature-lowering method to the point seed technique.Nowadays most crystals NIF using is grown by the point seed technique.To further improve the crystal utilization,cost-saving and growth rate,to study the orientation growth method of(D)KDP crystals is necessary.In this paper,we have studied and discussed the orientation growth method,macroscopic and microscopic aspects of the growth mechanism and its optical properties of(D)KDP crystals,to lay the foundation for optimizing the orientation growth method of(D)KDP crystals and improving the properties of(D)KDP crystals in ICF application.The primary coverage is as follows:1.The orientation growth method of(D)KDP crystals is analyzed.The growth mechanism of(D)KDP crystal is studied,for macroscopic growth mechanism,dead zone and growth rate of(D)KDP solution of same deuteration level was studied.And the correlativity between(D)KDP solution saturation temperature and dead zone range was found:with the decrease of the saturation temperature of the solution,the dead zone range is wave increase.For microscopic growth mechanism,characterization of crystal surface morphology by Atomic Force Microscopy,correlativity between solution super saturation,point seed cut type and step distribution of crystal cylinder was found.The key processes to be pay attention during crystal growth are studied.(D)KDP crystals of different point seed type are grown.Pictures of(D)KDP crystals of different point seed type grown successfully or failed were taken.(D)KDP crystals grown by ab direction point seed prefer growing higher to extending cylinder.It will reach the edge of the crystal growth platform before it gets appropriate aspect ratio,so that the available part of(D)KDP crystals will be less.Based on the studies above,we could control the crystal growth rate by controlling the rate of temperature lowering so that we could control the aspect ratio of the crystal to improve the crystal utilization.2.Property of(D)KDP crystals grown on different point seed type were studied systematically.The crystalline perfection of(D)KDP crystals grown on different type point seed is studied by testing the rocking curves and measuring the FWHM.It shows that the crystalline perfection of(D)KDP crystals grown on 59 ° or ab direction point seed is with the best of that of Z direction point seed.We also tested the transmittance spectra to measure the optical properties of(D)KDP crystals grown on different type point seed.And we find little difference between transmittance of(D)KDP crystals grown on type different point seed.By comparing the LTD and 3?efficiency of DKDP crystal grown on different type point seed,we found that(D)KDP crystals grown on 59 ° or ab direction point seed perform worse than(D)KDP crystals grown on Z direction point seed,and the LTD and 3? efficiency of(D)KDP crystals grown on 59 ° direction point seed is higher than that of ab direction point seed.