扫描电镜加工铌酸锂晶体电畴反转光栅的研究

本文简单介绍了非线性晶体相位匹配和铌酸锂光波导准相位匹配倍频原理，开展了扫描电子显微镜电子束辐照反转极化实验，分析了实验结果，摸索出合适的工艺条件，证明利用扫描电镜可以加工出满足准相位匹配条件的电畴反转我栅。     

有效倍频行为中相位匹配条件的适用范围

任何一种理论都有它的适用范围,相位匹配条件亦不例外,因此我们可以问是否存在一个判据,它告诉我们什么时候可以“相位匹配地”讨论有效倍频现象以及什么时候必须“非相位匹配地”讨论。本文基于晶体的离散原子结构状态讨论了有效倍频行为中先前Franken和Ward所描述的相位匹配条件的适用范围,粗略地说,每当所有有关的光波波长都比晶格中原子间距大得多时,“相位匹配地”讨论就足够了,也即是足够精确了。     

准相位匹配LiNbO3波导全光波长变换的理论研究

对周期性极化LiNbO3(PPLN)光波导实现准相位匹配全光波长变换进行了理论研究,得出了提高准相位匹配和全频光波长变换效率的有效途径,为准相位匹配全光波长变换器的研制提供了理论指导。     

二次晶体中准相位匹配孤子的激发与传输

采用分步积分法,研究了形状为双曲正割平方的光束在线性和非线性极化率均被调制的一维准相位匹配(QPM)二次晶体中的传输特性.数值计算表明,在仪有基波(FW)注入的情况下,基波迅速激发出基态孤子,并呈现出固有的振荡态,二次谐波(SHW)虽然激发出谐波孤子,但相应的色散波现象比较明显;在同时注入基波与二次谐波的情况下,当它们的振幅和光束宽度满足一定条件时,两者均能够激发出稳定的孤子态,并且基态孤子的振荡更具周期性,二次谐波的色散波现象显著减弱.同时,注入的二次谐波的振幅存在一个临界值,可使激发的二次谐波孤子达到最佳孤子态.     

准相位匹配砷化镓晶体制备工艺及脉冲CO_2激光倍频研究

对准相位匹配砷化镓(GaAs)晶体扩散键合制备方法进行了研究。采用超高真空预键合-高温退火方法,在不同载荷压力条件下,完成了三组准相位匹配GaAs倍频晶体的制备。准相位匹配结构的极化周期长度为219μm,堆叠层数44层,直径18mm,有效通光孔径达到15mm,在通光面未镀膜条件下,最高的基频光与倍频光透射率在30%以上。以主脉冲宽度90ns,拖尾宽度2~6μs的横向激励大气压(TEA)-CO2激光器作为基频光光源,通过调谐基频光波长,在4.63~5.37μm波段内得到了效率大于4%的倍频输出。当基频光波长为10.68μm,主脉冲能量为409mJ,晶体接收基频光功率密度达到3.65MW/cm2时,得到了单脉冲能量26.9mJ,峰值功率298kW,倍频效率达到6.58%的倍频输出。     

影响CO2激光准相位匹配倍频效率的理论研究

对影响CO2激光准相位匹配倍频效率的因素进行了研究, 利用非线性耦合波动方程, 分析了在不同基频光功率密度条件下, 倍频过程中晶体吸收、界面损耗、周期长度误差和温度变化对倍频效率的影响; 对制备高效率CO2激光倍频晶体的误差容限参数进行了计算。当基频光强度为25 MW/cm2, 晶体键合层数为60层时, 必须将每层界面损耗控制在0.5%以下, 周期长度误差控制在1 μm以内, 能保证理论倍频效率40%, 为准相位匹配晶体的制备参数的确定提供理论依据。     

准相位匹配光参量振荡器理论研究与优化设计

研究了准相位匹配条件下光学参量振荡理论,对单谐振情况下参量增益同极化反转周期的关系进了讨论;从理论上详细地分析了准相位匹配参量振荡器中谐振腔长度、晶体长度、抽运光脉宽以及信号光输出透过率对建立振荡所需泵浦光能量阈值大小的影响,并通过实验验证了理论分析的适用性.     

Manipulation of Conductive Domain Walls in Confined Ferroelectric Nanoislands

Conductive ferroelectric domain walls—ultranarrow configurable conduction paths—have been considered as essential building blocks for future programmable domain wall electronics. For applications in high‐density devices, it is imperative to explore the conductive domain walls in small confined systems, while earlier investigations have hitherto focused on thin films or bulk single. Here, an observation and manipulation of conductive domain walls confined within small BiFeO₃ nanoislands aligned in high‐density arrays are demonstrated. Using conductive atomic force microscopy, various types of conductive domain walls, including the head‐to‐head charged domain walls (CDWs), zigzag domain walls, and typical 71° head‐to‐tail neutral domain walls (NDWs), are distinctly visualized. The CDWs exhibit remarkably enhanced metallic conductivity with current of ≈nA order in magnitude and 10⁴ times larger than that inside domains (0.01–0.1 pA), while the semiconducting NDWs allow much smaller current (≈10 pA) than the CDWs. The substantial difference in conductivity for dissimilar walls enables manipulations of various wall conduction states for individual addressable nanoislands via electrical tuning of domain structures. A controllable writing of four distinctive states in individual nanoislands can be achieved, showing application potentials for developing multilevel high‐density memories.     

铁电多层畴结构中铁电畴层波振动模式的频谱分析

本文首次对多层畴结构中的振动模式进行了实验研究,观察到了一系列大小相当的中心峰,这对应于不同中心同步频率下激发的不同的振动模。通过频谱分析,获得了3,4,5层畴层结构的色散曲线。     

小时带积反射栅脉压线

小时带积线性调频信号由于其频谱存在着严重的菲氏波动，从理论上限制了压缩脉冲的旁瓣抑制能力。而实际制作中由于受工艺和再生信号的影响，旁瓣抑制会更差些。文章报道利用声表面波反射技术，在锗酸铋压电材料上研制出时带积为３０、旁瓣电平抑制优于－３２ｄＢ的脉压线，同时给出器件的性能参数和波形     

Emission Dipole and Pressure-Driven Tunability of Second Harmonic Generation in vdWs Ferroelectric NbOI2

2D in-plane ferroelectric NbOI₂ exhibits strong second harmonic generation (SHG) and ultrahigh effective susceptibility. To push forward their applications in nonlinear photonics and optoelectronics, it is highly desirable to understand the emission dipole orientation and tunability of SHG, which is not achieved. Here, by integrating tight focusing from parabolic mirror with back focal plane (BFP) imaging technique, for the first time it is demonstrated that SHG emission of NbOI₂ presents purely in-plane dipole orientation in consistent with numerical simulations, suggesting the in-plane components of the SHG susceptibility tensor in NbOI₂ dominate the emission. Moreover, with the aid of ab-initio calculations, it is found that the hydrostatic pressure can dramatically change the structure and resultant SHG intensity of NbOI₂. Explicitly, SHG intensity endures a slight increase due to the distortion of octahedral at low pressure pressure, and then monotonously decreases due to the improvement of structural symmetry with further increasing pressure, and drastically quenching resulting from the ferroelectric to paraelectric phase transition. This work unambiguously demonstrates the dipole emission behavior of SHG and the relationship between structural evolution and SHG intensity, which provides an avenue for tunable nonlinear optics and optoelectronics.     

铁电畴层波的电光效应

铁电１８０°畴结构在超声波作用下将被诱导出沿畴壁传播的铁电畴层波，其电场导致了构成铁电１８０°畴结构的晶体的电光效应，畴结构的光率体发生了改变，晶体的主折射率受到激发铁电畴层波的超声波的调节。这一效应在声光控制和超声检测方面有应用价值。     

铁电畴层波的弹光效应

铁电１８０°畴结构在超声波作用下将被诱导出沿畴壁传播的铁电畴层波，其应变场导致了构成铁电１８０°畴结构的晶体的弹光效应，畴结构的光率体发生了改变，晶体的主折射率和双折射率受到激发铁电畴层波的超声波的调制，这一现象在声光控制和超声检测方面有应用价值。     

弛豫铁电陶瓷PST中反相畴结构的HREM研究

本工作用高分辨电子显微学方法研究了弛豫铁电陶瓷Ｐｂ（Ｓｃ０．５Ｔａ０．５）Ｏ３（ＰＳＴ）中的有序－无序结构，直接观察到有序－无序结构畴界及反相畴界（ＡＰＢｓ），对反相畴界的结构进行了分析，指出在ＰＳＴ中的反相畴往往是（１１１）面的层错，晶格位移在（１１１）方向上，位移量是１／２（１１１）。提出了在ＰＳＴ中ＡＰＢｓ形成的机制。     

中心对称材料中二次谐波产生的影响因素

介绍中心对称材料二次谐波产生(SHG)的基本原理,通过数值模拟计算,分析研究影响中心对称材料SHG的因素.其中,光子晶体带隙(PBG)的影响最为关键,它决定了SH能否产生;激励波入射角与组成结构的耦合介质柱和填充因子对SHG强度大小也有较大影响,按文中结构,耦合介质柱有2排已足够,最佳入射角为20°～30°,填充因子为0.6.     

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,respect...