Irradiation Effect on Second Harmonic Generation of Dyes Doped KDP Crystals

Most irradiation studies in the hydrogen bonded ferroelectrics have been concentrated on the transient defects induced by ionising radiation, such as ultraviolet （UV） light, where the defects are closely related to the optical properties. But heavy ion beam irradiation effects have rarely been studied. The structural, optical, and non-linear optical properties of the doped crystals were analyzed with the characterization studies, such as powder XRD, UV-Visible and second harmonic generation （SHG） measurements, respectively. The results for doped KDP crystal were compared with the results of the pure KDP crystals. The experiment results showed that Li^3＋ irradiation leads to the development of a well-defined surface H peak in dye doped KDP crystals. The stability of KDP single crystal was improved by doping organic dyes. The nano-islands of dye in KDP were likely to be dissolved and enhance the non-linear optical properties of these materials.

Full-band error control and crack-free surface fabrication techniques for ultra-precision fly cutting of large-aperture KDP crystals

Large-aperture potassium dihydrogen phos- phate （KDP） crystals are widely used in the laser path of inertial confinement fusion （ICF） systems. The most common method of manufacturing half-meter KDP crystals is ultra-precision fly cutting. When processing KDP crystals by ultra-precision fly cutting, the dynamic characteristics of the fly cutting machine and fluctuations in the fly cutting environment are translated into surface errors at different spatial frequency bands. These machin- ing errors should be suppressed effectively to guarantee that KDP crystals meet the full-band machining accuracy specified in the evaluation index. In this study, the anisotropic machinability of KDP crystals and the causes of typical surface errors in ultra-precision fly cutting of the material are investigated. The structures of the fly cutting machine and existing processing parameters are optimized to improve the machined surface quality. The findings are theoretically and practically important in the development of high-energy laser systems in China.

阴离子杂质对KDP晶体生长习性的影响及快速生长研究

Great interest is being focused on the growth technique of KDP crystal,the first choice material for the fabrication of frequency converter and electro optic switcher used in the studies of inertial confinement fusion (ICF).To reduce the cost of growth,scientists are endeavoring to promote the growth rate.The“point seed” method is one of rapid growth techniques recently developed by Lawrence Livermore National Laboratory.In the former technique,crystals are grown in all three directions at an averaged rate of 10 15mm/day. Impurities are regarded as one of the factors to inhibit the growth rate.It is generally accepted that high valence cationic ions,such as Fe 3+ ,Cr 3+ ,Al 3+ ,etc,are easy to be adsorbed on the prismatic faces and inhibit their growth.Some anions,especially those have ability to form strong hydra bond,such as phosphate derivatives (polyphosphate,metaphosphate,pyrophosphate,etc) have significant inhibiting effects on the growth of KDP pyramidal face.It is suggested that the H bonding is the key interaction force between the growing surface and the impurities.

大尺寸KDP晶体生长

KDP and its deuterated analog DKDP (K (D x H 1- x ) 2PO 4) are the first ch oice materials in the fabrication of optical switcher and frequency converter fo r inertial confinement fusion study.In the past years,the growth technique has b een d eveloped greatly.Large aperture crystals can be grown with various methods,such as,temperature decreasing,solution circular flow,and rapid growth method,which i ntend to reduce the cost of production and satisfy the requirement of ICF.As to rapid growth method,much attention has been paid to solution stability and the K DP crystal qualities of this method which has been proved that high speed can be obtained.LLNL has grown KDP crystal with dimension of 57mm×57mm×55mm,260 kil ogram in 59 days.This method is very different from conventional method for grow ing KDP crystal in three directions uniformly.In addition to the growth of the pyramidal faces,rapid crystallization from supersaturated solution results in si gnificant growth of prismatic faces.Inclusions of growth solution and incorporat ion of metal impurities will occur in the prism sector as prism extends very muc h by this method.Fast growth needs high supersaturation(10%—30%),so the grow th condition,such as ,raw materials,apparatus,temperature lowing proceed should be controlled very strictly.In order to improve the utilization of KDP crystal g rown by point seed method,we developed 4 vessels circular technique on the bas e of 3 vessels circular technique recently.

Subsurface Damage in Scratch Testing of Potassium Dihydrogen Phosphate Crystal

Potassium dihydrogen phosphate （KDP） is an important electro-optic crystal, often used for frequency conversion and Pockels cells in large aperture laser systems. To investigate the influence of anisotropy to the depth of subsurface damage and the profiles of cracks in subsurface of KDP crystal, an experimental study was made to obtain the form of subsurface damage produced by scratches on KDP crystal in [100], [120] and [110] crystal directions on （001） crystal plane. The results indicated that there were great differences between depth and crack shape in different directions. For many slip planes in KDP, the plastic deformation and cracks generated under pressure in the subsurface were complex. Fluctuations of subsurface damage depth at transition point were attributed to the deformation of the surface which consumed more energy when the surface deformation changed from the mixed region of brittle and plastic to the complete brittle region along the scratch. Also, the process of subsurface damage from shallow to deep, from dislocation to big crack in KDP crystal with the increase of radial force and etch pit on different crystal plane were obtained. Because crystallographic orientation and processing orientation was different, etching pits on （100） crystal plane were quadrilateral while on （110） plane and （120） plane were trapezoidal and triangular, respectively.

Thermo-optic characterization of KDP single crystals by a modified Snarmont setup for electro-optic modulation system

For our KDP crystal orientation, various tbermo-optic （TO） and relevant temperature-dependence param- eters are defined, presented, and studied in the framework of a transverse and a longitudinal electro-optic （EO） modulation systems. This study is based on the concept of the so-called opto-electrical bias （~） ap- plied to the system. For both of the above EO-modulation systems, a set of original equations is extracted and investigated with regard to each of the more important TO or temperature coefficients. Using these equations, for these parameters the role of the transverse configuration is examined in comparison with its corresponding longitudinal configuration. A comparison is done with other orientation of the same KDP crystal.

Rapid growth of a long-seed KDP crystal

To reduce the seed length while maintaining the advantages of the cuboid KDP-type crystal,a long-seed KDP crystal with size 471 mm×480 mm×400 mm is rapidly grown.With almost the same high cutting efficiency to obtain third harmonic generation oriented samples,this long-seed KDP-type crystal can be grown with a shorter seed than that of the cuboid KDP-type crystal.The full width at half maximum of the high-resolution X-ray diffraction of the(200)crystalline face is 28.8 arc seconds,indicating that the long-seed KDP crystal has good crystalline quality.In the wavelength range of 377–1022 nm,the transmittance of the long-seed KDP crystal is higher than 90%.The fluence for the 50%probability of laser-induced damage(LID)is 18.5 J/cm^2(3 ns,355 nm).Several test points survive when the laser fluence exceeds 30 J/cm^2(3 ns,355 nm),indicating the good LID performance of the long-seed KDP crystal.At present,the growth of a long-seed DKDP crystal is under way.

Nanoindentation on the doubler plane of KDP single crystal

The nanohardness is from 1.44 to 2.61 GPa,the Vickers hardness is from 127 to 252 Vickers,and elastic modulus is from 52 to 123 GPa by the nanoindentation experiments on the doubler plane of KDP crystal. An indentation size effect is observed on the doubler plane in the test as the nanohardness and elastic modulus decreases with the increase of the maximum load.Slippage is identified as the major mode of plastic deformation, and pop-in events are attributed to the initiation of slippage.And the variation of unloading curve end is the result of stick effects between the indenter and the contact surface.The depth of the elastic deformation,which is between 40 and 75 nm,is responsible for the elastic deformation.The doubler plane of KDP crystal has anisotropy,and the relative anisotropy of nanohardness is 8.2%and the relative anisotropy of elastic modulus is 8.0%.

Elastic-plastic-brittle transitions of potassium dihydrogen phosphate crystals:characterization by nanoindentation

Potassium dihydrogen phosphate(KDP)crystals are widely used in laser ignition facilities as optical switching and frequency conversion components.These crystals are soft,brittle,and sensitive to external conditions(e.g.,humidity,temperature,and applied stress).Hence,conventional characterization methods,such as transmission electron microscopy,cannot be used to study the mechanisms of material deformation.Nevertheless,understanding the mechanism of plastic-brittle transition in KDP crystals is important to prevent the fracture damage during the machining process.This study explores the plastic deformation and brittle fracture mechanisms of KDP crystals through nanoindentation experiments and theoretical calculations.The results show that dislocation nucleation and propagation are the main mechanisms of plastic deformation in KDP crystals,and dislocation pileup leads to brittle fracture during nanoindentation.Nanoindentation experiments using various indenters indicate that the external stress fields influence the plastic deformation of KDP crystals,and plastic deformation and brittle fracture are related to the material's anisotropy.However,the E l Ning Hou 13b908074@hit.edu.cn Liang-Chi Zhang liangchi.zhang@unsw.edu.au 1 School of Mechatronics Engineering,Harbin Institute of Technology,Harbin 150001,People's Republic of China 2 School of Mechatronics Engineering,Shenyang Aerospace University,Shenyang 110136.People's Republic of China'Laboratory for Precision and Nano Processing Technologies,School of Mechanical and Manufacturing Engineering,The University of New South Wales,Sydney,NSW 2052,Australia effect of loading rate on the KDP crystal deformation is practically negligible.The results of this research provide important information on reducing machining-induced damage and further improving the optical performance of KDP crystal components.

Understanding the formation mechanism of subsurface damage in potassium dihydrogen phosphate crystals during ultraprecision fly cutting

Potassium dihydrogen phosphate(KDP)crystals play an important role in high-energy laser systems,but the laser damage threshold(LDT)of KDP components is lower than expected.The LDT is significantly influenced by subsurface damage produced in KDP crystals.However,it is very challenging to detect the subsurface damage caused by processing because a KDP is soft,brittle,and sensitive to the external environment(e.g.,humidity,temperature and applied stress).Conventional characterization methods such as transmission electron microscopy are ineffective for this purpose.This paper proposes a nondestructive detection method called grazing incidence X-ray diffraction(GIXD)to investigate the formation of subsurface damage during ultra-precision fly cutting of KDP crystals.Some crystal planes,namely(200),(112),(312),(211),(220),(202),(301),(213),(310)and(303),were detected in the processed subsurface with the aid of GIXD,which provided very different results for KDP crystal bulk.These results mean that single KDP crystals change into a lattice misalignment structure(LMS)due to mechanical stress in the subsurface.These crystal planes match the slip systems of the KDP crystals,implying that dislocations nucleate and propagate along slip systems to result in the formation of the LMS under shear and compression stresses.The discovery of the LMS in the subsurface provides a new insight into the nature of the laser-induced damage of KDP crystals.

Experimental study on high-efficiency polishing for potassium dihydrogen phosphate (KDP) crystal by using two-phase air-water fluid

A high-efficiency polishing approach using two-phase air–water fluid(TAWF)is proposed to avoid surface contamination and solve the inefficiency of previous water-dissolution polishing techniques for potassium dihydrogen phosphate(KDP)crystal.In the proposed method,controllable deliquescence is implemented without any chemical impurity.The product of deliquescence is then removed by a polishing pad to achieve surface planarization.The mechanism underlying TAWF polishing is analyzed,a special device is built to polish the KDP crystal,and the effect of relative humidity(RH)on polishing performance is studied.The relationship between key parameters of polishing and surface planarization is also investigated.Results show that the polishing performance is improved with increasing RH.However,precisely controlling the RH is extremely difficult during TAWF polishing.Controllable deliquescence can easily be disrupted once the RH fluctuates,which therefore needs to be restricted to a low level to avoid its influence on deliquescence rate.The material removal of TAWF polishing is mainly attributed to the synergistic effect of deliquescence and the polishing pad.Excessive polishing pressure and revolution rate remarkably reduce the life of the polishing pad and the surface quality of the KDP crystal.TAWF polishing using IC-1000 and TEC-168S increase the machining efficiency by 150%,and a smooth surface with a root mean square surface roughness of 5.5 nm is obtained.

Nano-indentation study on the(001) face of KDP crystal based on SPH method

In order to avoid the defects of mesh distortion when dealing with large deformation problems through using the finite element method, a mess-free simulation method--smooth particle hydrodynamics （SPH） has been introduced. The material constitutive model of KDP crystal has been established based on the elastic-plastic theory. Then the nano-indentation on the （001） face of KDP crystal has been carried out using SPH method. Simulation results show that the maximum equivalent stress and the maximum plastic strain concentrate on the area that located near the tip of the indenter during the loading process. The distribution shape of Von Mises stress is similar to concentric circles. During the unloading process, no obvious variation of plastic strain distribution exists. The maximum Von Mises stress is mainly located at the indentation and its edge at the end of the unloading process. The approximate direct proportion relationship between the maximum indentation depth and the depth of the maximum Von Mises stress distribution has been discovered when the maximum load is lower than 8 mN. In addition, the nano-indentation experiments on KDP crystal＇s （001） face have been carried out. Both the material parameters and the adjusted stress-strain curve have been verified. The hindering role of the affected layer has been found and analyzed.

Material removal mechanisms and characteristics of potassium dihydrogen phosphate crystals under nanoscratching

Potassium dihydrogen phosphate(KDP)crystals are important materials in high-energy laser systems.However,because these crystals are brittle and soft,machining-induced defects often emerge in KDP components.This study aimed to investigate the material removal mechanisms and characteristics of KDP during nanoscratching using Berkovich,spherical,and conical indenters.We found that KDP surface layers could be removed in a ductile mode at the micro/nanoscale and that dislocation motion was one of the main removal mechanisms.Removal characteristics are related to the stress fields generated by indenter geometries.The spherical indenter achieved a ductile removal mode more easily.The lateral force of nanoscratching increased with an increase in the normal force.The coefficient of friction(COF)followed the same trend as the lateral force when spherical and conical indenters were used.However,the COF was independent of the normal force when using a Berkovich indenter.We found that these COF variations could be accurately described by friction models.