氘化对KH2PO4晶体微观缺陷影响的正电子湮没研究

采用传统降温法从不同程度氘化(x=0, 0.51, 0.85)的生长溶液中生长氘化KH₂PO₄(KDP) 晶体, 利用正电子湮没技术(正电子寿命谱和多普勒展宽谱)、结合X射线衍射谱(XRD) 结构分析, 对KDP晶体氘化生长的微观缺陷进行了研究, 讨论了氘化程度对晶体内部微观结构特性、缺陷类型和浓度的影响. XRD结果显示晶胞参数a, b值随氘含量的增加而增加, c值无明显变化; 正电子寿命谱结果发现随着氘化浓度的提高, KDP晶体内部中性填隙缺陷以及氧缺陷不断增加, 引起晶体晶格畸变; 氢空位、K空位、杂质替位缺陷不断发生缔合反应形成复合缺陷, 缺陷浓度不断减少; 团簇、微空洞等大尺寸缺陷也在不断发生聚合反应, 缺陷浓度表现为不断减少. 多普勒实验结果表明随着氘化程度的提升, 晶体内部各类缺陷表现为同步变化. 实验结果表明, KDP晶体在低浓度氘化生长(50%以内)下缺陷反应较弱, 而在高浓度氘化(50%以上)下的缺陷反应显著增强.     

CO_2激光光栅式扫描修复熔石英表面缺陷的实验研究与数值模拟

基于熔石英材料对波长为10.6μm的CO2激光具有强吸收作用这一特点,提出采用CO2激光光栅式多次扫描修复熔石英光学元件表面密集分布的划痕和抛光点等缺陷的方法.实验结果表明,在合理的扫描参数下,元件表面的划痕和抛光点等缺陷可被充分地消除.损伤阈值测试结果表明,表面划痕和抛光点等缺陷被完全消除的元件的损伤阈值可回复到或超过基底的损伤阈值.同时结合有限元软件Ansys的模拟结果分析了CO2激光扫描修复及消除元件表面划痕和抛光点等缺陷的过程.本文为消除元件表面划痕和抛光点等缺陷提供了非常有意义的参考.     

激光诱导熔石英表面损伤修复中的气泡形成和控制研究

基于熔石英材料在CO_2激光作用下的温度分布和结构参数变化的计算结果,对熔石英损伤修复中的气泡形成和控制进行了研究.针对损伤尺寸介于150—250μm之间的损伤点,提出了一种能够有效控制气泡形成的长时间低温预热修复方法.基于低温下熔石英材料结构弛豫时间常数较长的特点,该方法在不引起熔石英材料结构发生显著变化的同时,能够解吸附表面和裂纹处所附着的气体和杂质,可有效降低裂纹闭合过程中气泡形成的概率.实验结果表明,长时间低温预热修复方法的成功修复概率可达到98%.     

熔石英损伤修复坑下游光场调制的数值模拟与实验研究

系统研究了熔石英激光损伤修复后的形貌特征,根据测量数据建立了典型的损伤修复坑三维模型,利用标量衍射理论并结合快速傅里叶变换算法研究了修复坑在351 nm激光辐照下游光场调制的分布规律.研究表明,修复坑引起的光场调制会使得下游不同距离位置处出现环形光场增强区和轴上位置光场增强点;环形光场增强区位置距离修复元件较近,其环形调制极大值主要受修复坑深度的影响,且随修复坑深度的增大而逐渐增加;轴上位置光场增强点位置距离修复元件较远,其轴上调制极大值主要受修复坑边缘凸起高度的影响,且随凸起高度的增大而快速增加;环形调制极大值或轴上调制极大值增大的同时,其分布位置与修复元件之间的距离均会逐渐减小.实验验证表明,利用三维修复坑模型得到的下游光场调制数值模拟结果与实验测量结果具有较好的一致性.本研究结果对控制熔石英元件损伤修复形貌特征以抑制调制增强效应给出了具体的控制方向,对修复工艺的改进与完善提供了非常有意义的参考.     

浓醪乙醇发酵的单细胞拉曼光谱表征

应用激光镊子拉曼光谱技术收集500L发酵罐中木薯淀粉浓醪乙醇发酵过程底物、产物及酵母单细胞的拉曼光谱,以期从单细胞水平为乙醇发酵提供新的认识。结果显示:1)拉曼光谱可以实时监测浓醪乙醇发酵过程底物与产物的变化;2)酵母细胞胞内物质的变化存在类似于产物变化的前发酵期、主发酵期和后发酵期3个阶段,但出现的时间要比产物变化晚约4h;3)为适应浓醪发酵环境,酵母细胞的生理状态和胞内物质在不断地进行调整,随着环境乙醇浓度的升高,酵母细胞在胞内累积蛋白质和脂类物质,蛋白质二级结构逐渐变为以无规则卷曲为主;4)发酵后期,酵母细胞在胞内累积大量的嘌呤类物质,但细胞间含量存在异质性。上述结果表明,单细胞拉曼光谱技术提供了一种研究微生物发酵的新方法,可从新的角度获知乙醇发酵过程酵母细胞内外的变化信息。     

乙酸胁迫酵母细胞凋亡过程中单个线粒体损伤的拉曼光谱分析

应用激光光镊拉曼光谱技术(LTRS)作为一种非入侵分析线粒体的工具,结合氧电极法、紫外分光光度计法,研究乙酸胁迫酵母细胞后提取的线粒体,以及直接胁迫正常酵母细胞的离体线粒体的拉曼光谱.结果显示,乙酸胁迫酵母细胞后提取的线粒体的拉曼光谱,归属于核酸的谱峰(1081和1301 cm-1)、蛋白质的谱峰(872,1445,1604和1657 cm-1)、脂类的谱峰(1125,1301,1445和1657 cm-1)、Cyt c的特征峰(750和1125 cm-1)、线粒体呼吸特征峰(1604 cm-1),都随着诱导程度的加深而降低,与常规法测定的指标呼吸率,磷氧比,细胞色素C含量的降低,MDA含量的升高的变化趋势相似;乙酸直接胁迫线粒体的拉曼光谱,归属于核酸的谱峰(1081和1301 cm-1),蛋白质的谱峰(872,1445,1604和1657 cm-1),脂类的谱峰(1125,1301,1445和1657 cm-1),Cyt c的特征峰(750和1125 cm-1),线粒体呼吸特征峰(1604 cm-1),都随着诱导程度的加深而降低,与常规法测定的指标呼吸率、磷氧比、细胞色素C含量的降低,MDA含量的升高的变化趋势相似.结果表明,乙酸胁迫细胞过程中,乙酸进到细胞内可能直接作用于线粒体,引起线粒体内物质的释放,导致依赖于线粒体途径的细胞凋亡.     

乙醇胁迫酵母凋亡过程的单细胞喇曼光谱

在群体细胞水平和单个酵母细胞水平上,应用光镊喇曼光谱技术对高浓度乙醇胁迫过程中细胞内生物大分子物质的动态变化进行实时监测.基于两种水平上的研究结果显示:在高浓度乙醇胁迫下,归属于核酸的喇曼峰(721,1 083,1 301cm-1)、归属于蛋白质的喇曼峰(721,858,1 001,1 301,1 445,1 608,1 657cm-1)和归属于脂类(1 083,1 301,1 445cm-1)喇曼峰的峰强度都随处理时间的延长而显著降低,说明了高浓度乙醇诱导酵母凋亡过程中核酸、蛋白质、脂类等物质的含量是逐渐降低的.结合单因素分析法与重复测量分析法发现,群体细胞与单个细胞光谱的变化有明显差异性,反映基于群体细胞的研究,个体细胞的信息被平均光谱信息所掩盖,无法体现个体间所存在的差异.应用激光镊子喇曼光谱技术基于单个细胞水平上的研究能更直接、真实地反映高浓度乙醇胁迫下细胞内生物大分子变化的动态信息.     

化学增透膜激光疲劳损伤效应

疲劳效应是诱导高功率固体激光装置中光学元件激光损伤的因素之一,目前对SiO₂化学增透膜激光诱导疲劳损伤的研究鲜见报道。基于此,本文采用单一激光能量多发次辐照和多梯度激光能量多发次辐照两种不同的激光辐照方式,研究1064 nm化学增透膜层的激光疲劳损伤效应及特征。研究结果表明,在单一激光能量多发次脉冲激光辐照下,膜层最易发生疲劳损伤; 采用多梯度激光能量多发次辐照的方式,可以有效地提升膜层的损伤阈值,进而提升膜层的抗激光疲劳损伤性能。     

Surface defects,stress evolution,and laser damage enhancement mechanism of fused silica under oxygen-enriched condition

Oxygen ions (O⁺) were implanted into fused silica at a fixed fluence of 1×10¹⁷ ions/cm² with different ion energies ranging from 10 keV to 60 keV. The surface roughness, optical properties, mechanical properties and laser damage performance of fused silica were investigated to understand the effect of oxygen ion implantation on laser damage resistance of fused silica. The ion implantation accompanied with sputtering effect can passivate the sub-/surface defects to reduce the surface roughness and improve the surface quality slightly. The implanted oxygen ions can combine with the structural defects (ODCs and E' centers) to reduce the defect densities and compensate the loss of oxygen in fused silica surface under laser irradiation. Furthermore, oxygen ion implantation can reduce the Si-O-Si bond angle and densify the surface structure, thus introducing compressive stress in the surface to strengthen the surface of fused silica. Therefore, the laser induced damage threshold of fused silica increases and the damage growth coefficient decreases when ion energy up to 30 keV. However, at higher ion energy, the sputtering effect is weakened and implantation becomes dominant, which leads to the surface roughness increase slightly. In addition, excessive energy aggravates the breaking of Si-O bonds. At the same time, the density of structural defects increases and the compressive stress decreases. These will degrade the laser laser-damage resistance of fused silica. The results indicate that oxygen ion implantation with appropriate ion energy is helpful to improve the damage resistance capability of fused silica components.     

Effect of structural parameters of Gaussian repaired pit on light intensity distribution inside KH_2PO_4 crystal

KH2PO4 （KDP） crystal with excellent optical properties is a very important element of inertial confinement fusion （ICF） device. However, KDP crystal surface micro-defects severely reduce the crystal laser damage threshold, affecting the crystal service life. In this paper, Gaussian repaired pit is used to replace the crystal surface micro-defects, in order to improve the laser damage resistance of the KDP crystal with surface micro-defects. At first, the physical model of Gaussian repaired pit is built by Fourier model method, and the accuracy of the method is analyzed. It is found that the calculation error can be reduced by increasing the product of the width-period ratio and the truncation constant of the repaired pit. The calculation results about the physical model of Gaussian repaired pit show that the light intensity distribution within the crystal is symmetrical, and there are evidently enhanced light intensity regions in the crystal. Meanwhile, the maximum relative intensity inside the KDP crystal decreases gradually with the increase of the width of the Gaussian repaired pit. Secondly, the Gaussian repaired pits with different widths and the same depth of 20 μm are processed by micro-milling. Their surfaces are very smooth and present the ductile cutting state under the microscope. Finally, the laser damage threshold of the Gaussian repaired pits on the surface of the KDP crystal sample is measured by a 3 ω, 6-ns laser. The results showthat the maximum threshold of the Gaussian repaired pits is 3.12 J/cm2, which is 60% higher than the threshold of initial damage point, and the laser damage threshold increases with the increase of the width of the Gaussian repaired pit.