二维平动长籽晶KDP类晶体循环过滤生长技术研究

Two-Dimensional Translational Growth and Properties of Long-Seed KDP-Type Crystals

瞄准KDP类晶体12 J/cm^(2)激光损伤阈值,从改善晶体生长表面的溶质分布情况着手,围绕新型KDP类晶体生长方法——二维平动技术全过程进行了初步研究。从生长设备、点晶方式、生长工艺等方面,研究了不同平移速度、平移加速度等生长参数下的晶体生长工艺。针对长籽晶点晶过程及成锥过程中易诱发杂晶产生的问题,提出了螺旋式点晶方式,将籽晶通过螺纹稳定地固定在晶盘上,使籽晶平移运动时产生的晃动幅度减小,从而减小对生长溶液的扰动。针对KDP类晶体生长对装置的要求,笔者设计并搭建了一套满足晶体二维平动生长要求的实验装置。通过紫外-可见吸收光谱、抗激光损伤阈值、荧光光谱等对晶体的性能进行分析,结果表明,在该二维平动生长方式下生长的晶体具有良好的光学质量以及较高的激光损伤阈值。

Objective KDP-type crystals are excellent nonlinear optical crystal materials that have a high laser threshold,wide transmittance band,high electro-optical coefficient,optical uniformity,and large size.Inertial confinement fusion(ICF)driven by high-power lasers has several requirements for crystal materials,such as a large aperture,a high laser damage threshold,large nonlinear optics,a wide transmission band,and low refractive index inhomogeneity.Thus far,only KDP-type crystals have met these requirements.Therefore,large KDP-type crystals are the only crystalline materials that can be used as electro-optical switches and frequency-conversion devices in ICF.The rapid growth method of KDP-type crystals eliminates the 0.5 mm/d growth rate limit of the traditional growth method and shortens the growth cycle from 2‒3 years to 4‒5 months.However,with the continuous power increase in ICF experiments worldwide,the requirements for KDP/DKDP crystals(particularly laser damage resistance)are increasing.Therefore,research on crystal growth remains significant.The key factor affecting the quality of crystal growth is the distribution of the solute concentration,which depends on the convective mode on the crystal surface.The two-dimensional growth mode allows the crystal surface to achieve a periodic reversible shear flow and improves the distribution uniformity of the solute concentration on the crystal surface.Methods To meet the requirements of the KDP crystal growth device,a set of experimental devices for two-dimensional crystal growth was designed and built.The device includes a growth tank,two-dimensional moving platform,and continuous filtration system.A temperature test was performed on the device to ensure that the temperature of the growth tank met the design requirements.To address the sealing problem of a crystal growth vessel(growth tank),a set of water-sealing devices that can satisfy the sealing demand of the tank was designed.A continuous filtration system can effectively reduce the particle concentration of a solution without affecting its stability.To reduce heterocrystal generation during the placement of long-seed crystals,a new spiral seed crystal method was proposed.The seed crystal was stably fixed on the crystal plate through a thread,which reduced the shaking amplitude and growth solution disturbance during the translation movement.Results and Discussions The two-dimensional KDP crystals have stronger absorption in the ultraviolet region.With an increase in translation velocity,the absorption first decreases and then increases.The translation velocity of 50 mm/s is better than those of 20 mm/s and 80 mm/s.The absorption of the crystal in the ultraviolet region is lower than that in the plane.The absorption of the crystal in the ultraviolet band can be reduced by decreasing its acceleration during the translational motion.The laser damage resistance of a crystal is closely related to its UV absorption performance.The 50%damage probability of the crystal with a translational speed of 50 mm/s is higher than those at 20 mm/s and 80 mm/s.The laser damage resistance of the crystal with the edge facing flow is higher than that with the face facing flow.The laser damage resistance of the crystals with an acceleration of 25 mm/s2 is better than that of 80 mm/s2.This is consistent with the ultraviolet absorption of the crystal;the absorption coefficient is high,and the resistance to laser damage is poor.Conclusions Based on the rapid growth of long-seed crystals,the two-dimensional translational growth technology of KDP crystals is explored.Equipment for two-dimensional translational growth was built,including a growth tank,two-dimensional moving platform,and continuous filtration system.A series of crystal growth processes were explored using this equipment.The grown crystals exhibit good transparency.The properties of the crystal were tested,including its optical properties,laser damage resistance,growth parameters,and mechanism.The absorption of the two-dimensional KDP crystals in the ultraviolet region is stronger.With an increase in translation velocity,the absorption first decreases and then increases.The absorption of the crystal in the ultraviolet region is lower than that in the plane.The absorption of the crystal in the ultraviolet band can be reduced by decreasing its acceleration during the translational motion.The laser damage resistance of the crystal is closely related to its UV absorption performance.The 50%damage probability of the crystal with a translational speed of 50 mm/s is higher than those at 20 mm/s and 80 mm/s.The laser damage resistance of the crystal with the edge facing flow is higher than that with the face facing flow.The laser damage resistance of the crystals with an acceleration of 25 mm/s2 is better than that of 80 mm/s2.