Second Harmonic Generation in TlInS2 Crystals

The temperature dependence of the generation of the second optical harmonic in TlInS₂ crystals in the vicinity of the phase transitions high–temperature–incommensurate–polar phases is investigated. It is shown that radiation in the incommensurate phase occurs only when the fundamental wave propagates along the axis of the superstructure of a crystal and the presence of radiation for certain geometries of the experiment confirms the symmetry group C ₂ ³ of the low–temperature polar phase. The dependence of the spectra on the periodic temperature change is attributed to the occurrence of long–lived metastable states.     

Optical Properties of [(CH3)2NH2]5Cd3Cl11 Crystals in the Region of their Phase Transitions

A sequence of phase transitions in the [(CH₃)₂NH₂]₅Cd₃Cl₁₁ (DMACC) crystal has been verified based on the study of temperature dependences of the optical birefringence and the data of piezooptical investigations. Absorption spectra in the visible and near-UV regions and IR reflection spectra in the 200–2000-cm^–1 region have been obtained. Phase transitions at temperatures of 179.5, 151, and 120 K have been detected. For all the phases of the DMACC crystal, the optical absorption edge obeys Urbach's empirical rule. It is shown that the phonons corresponding to the internal vibrations of the (Cd₃Cl₁₁)^5– polyhedron participate in the edge formation.     

Manifestation of Spatial Modulation in the Vibration Spectra of (N(CH3)4)2CuCl4 Crystals

The specific manifestations of the spatial modulation in the vibration spectra of (N(CH₃)₄)₂CuCl₄ crystals have been investigated. It has been shown that because of the narrow temperature range of existence of the incommensurate phase and the complexity of the spectra being analyzed, reliable resolution of additional modes arising under the influence of both incommensurate and commensurate modulation is only possible using a computer approximation of the spectra obtained. In accordance with the theoretical models considered, additional modes have been observed mainly in the region of low-frequency skeletal vibrations exhibiting a marked dispersion.     

Phase transition and optoelectronic properties of MgH2

In this article, structural and electronic properties of MgH₂ have been studied. The aim behind this study was to find out the ground state crystal structure of MgH₂. For the purpose, density functional theory (DFT)-based full-potential linearized augmented plane wave (FP-LAPW) calculations have been performed in three different space groups: P4₂/mnm (α-MgH₂), Pa3 (β-MgH₂) and Pbcn (γ-MgH₂). It has been found that the ground state structure of MgH₂ is α-MgH₂. The present study shows that α-MgH₂ transforms into γ-MgH₂ at a pressure of 0.41 GPa. After further increase in pressure, γ-MgH₂ transforms into β-MgH₂ at a pressure of 3.67 GPa. The obtained results are in good agreement with previously reported experimental data. In all the studied phases, the behavior of MgH₂ is insulating and its optical conductivity is around 6.0 eV. The α-MgH₂ and γ-MgH₂ are anisotropic materials while β-MgH₂ is isotropic in nature.     

Manifestations of Phase Transitions and the Thermooptical-Memory Effect in the Absorption Spectra of (N(CH<Subscript>3</Subscript>)<Subscript>4</Subscript>)<Subscript>2</Subscript>CuCl<Subscript>4</Subscript> Crystals

The manifestations of phase transitions and the spatial modulation of the structure of the (N(CH₃)₄)₂CuCl₄ crystal in its absorption spectra have been investigated. It has been established that the thermooptical-memory effect manifesting itself in the absorption spectra of this crystal entirely corresponds to the model of ordering of defects and impurities in a sample with a modulated structure. It is shown that, as a result of stabilization of the crystal studied in the incommensurate phase, its symmetry and the symmetry of the metal-halogen complex in it lower depending on the defect wave. This manifests itself as a marked shift of the intraionic-absorption bands and an increase in their intensity. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 72, No. 3, pp. 386–390, May–June, 2005.     

Optical Absorption Study on the Conversion and Restoration of Color Centers in Pure KCI Crystals

The conversion and restoration processes of colour centers in pure KCI crystals were studied by optical absorption measurements. When the sample is heated the aggregative centers in it begin to dissolve to F centers, and the opposite process will take place, i.e. F centers will aggregate to form F₂, F₃, F₄centers if the samples are cooled down. It was found that the conversion and restoration processes are dependent on the annealing temperature and time. In our experiment, the samples were treated at various temperatures and time. In addition the restoration process for the 350°C treated sample was studied live. We found that the higher the annealing temperature is the slower the restoration in the samples proceed, and the conversion process maintained for a few minutes even after annealing treatment.     

传压介质对晶格振动和相变压力的影响——α-Bi2O3的高压拉曼光谱研究

 本文分别使用4∶1的甲醇-乙醇混合溶液和固态氩做传压介质测量α-Bi₂O₃的高压拉曼光谱。实验结果表明，传压介质对样品的谱线频移速率及相变压力有明显的影响。通过对拉曼光谱的分析认定，α-Bi₂O₃在高压下可能经历了一次结构相变，在准静水压和非静水压条件下的相变压力分别为23.1 GPa和20.4 GPa。     

d2,8电子体系共价效应对光谱的影响

在含过渡金属离子的半磁半导体的光学和磁学性质研究中,由于体系的共价性较强,d轨道不再是纯d轨道,而是混合轨道t2g或eg。相应地,需要引入两个共价因子Nt和Ne。建立在混合轨道上的含有共价因子的能量矩阵称为广义能量矩阵。建立了d2,8电子体系的(45×45)阶广义能量矩阵。在广义能量矩阵中,拉卡(Racah)参量A不再是相加常量,同时,d8电子体系不能简单地视为互补的d2空穴体系,因为它们的能量矩阵形式不同。Nt和Ne虽然是属于两个不同轨道的不同的共价因子,但在数值上不能有大的差别,因为考虑进共价效应后,拉卡静电参量A对能级计算有极大的影响。这意味着在通常的光谱拟合中所采用的BCΔ方案是好的近似。以上结论被应用于ZnS∶Ni2 的d-d跃迁谱,计算结果与实验符合。     

反斯托克斯拉曼光谱在BaTiO_3铁电相变研究中的应用

从理论上讨论了一阶和二阶斯托克斯与反斯托克斯拉曼散射截面的温度依赖关系;在２９３Ｋ至４０１Ｋ的温度范围内,测量了ＢａＴｉＯ３单晶斯托克斯和反斯托克斯过程的偏振拉曼光谱;通过对ＢａＴｉＯ３单晶斯托克斯和反斯托克斯拉曼光谱的综合分析,证实在Ｘ（ＺＺ）Ｙ几何配置下测量到的位于２７５和５１４ｃｍ－１处的强峰为一阶拉曼光谱。此结果支持了ＢａＴｉＯ３铁电相变机制的有序—无序模型。     

BaF2替代BaO 对钡镓锗酸盐玻璃光学性质的影响

在摩尔分数组成x(BaO),r(Ga2O),r(GeO2)为0．20,0．15,0．65的玻璃中,分别以摩尔分数0．05,0．10．0．15和0．20的BaF2替代BaO,研究了氟化物对玻璃折射率和光吸收性质的影响。结果表明,在玻璃中加入氟化物．玻璃折射率和色散降低,玻璃的紫外吸收边向短波侧迁移,而红外吸收边无明显变化。不含氟化物的氧化物玻璃中含有大量的OH基．这些OH基在2．24μm、2．97μm和4．23μm附近引起光吸收．在含氟化物的玻璃中,2．24μm的吸收峰消失,而2．97μm和4．23μm附近的吸收大大减弱。讨论了各OH基吸收峰的起源,利用计算机技术对2．97μm附近的OH基吸收峰进行了高斯峰分离。玻璃在2．24μm的弱吸收可能来自H2O分子的一个伸缩模和两个振动模的结合(p 2ρ)．4．23μm吸收带是由与非桥O形成强氢键的OH基(T-OH…O^--T)伸缩振动引起,而中心位于2．7～3．2μm的OH吸收带为受不同程度氢键影响的OH基伸缩振动吸收．这些吸收带叠加导致OH吸收带出现非对称性加宽,吸收中心随玻璃中OH含量不同发生移动。     

Influence of a Magnetic Field on the Nonlinear Optical Susceptibility of NiI2-Doped CdI2 Single Crystals

The influence of treatment in a magnetic field at low temperatures on the nonlinear optical properties of NiI₂-doped CdI₂ single crystals is investigated. The impurity ions in the interlayer space or more complex centers into which these ions enter can align on exposure to a magnetic field due to the interaction with the membrane vibrations of the lattice and create residual polarization in a specimen. This polarization causes redistribution of the electric charge on the bonds and improves the nonlinear optical properties of single crystals.     

Influence of Radiative Irradiation on the Optical and Electrical Properties of Crystalline Quartz

The influence of radiation on the optical properties of quartz crystals has been investigated. Using the methods of IR and Raman spectroscopy, the lattice dynamics associated with a change in the spectral characteristics of a number of the stretching and deformation vibrations of the crystal lattice upon irradiation of samples by gamma quanta and neutrons to high doses has been determined. The regularities of radiative modification of the spectral characteristics of certain fully symmetrical and degenerate modes of the stretching vibrations of hydroxide groups are determined. To elucidate the reasons for the changes in the optical spectra, the latter were compared with the corresponding spectra obtained upon heating of wafers and with the change in the conductivity of crystals caused by irradiation. It is assumed that the changes in the optical spectra and conductivity of irradiated crystals are mainly due to the rearrangement of the quartz structure and to the stimulated migration of impurities. A possible mechanism of the process of conduction in the material is discussed in the framework of the existing models.__________Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 72, No. 2, pp. 224–229, March–April, 2005.     

Influence of crystal synthesis on the incommensurate phase and lock-in transition of Rb2ZnCl4 crystals

A comparative study of several crystals of Rb₂ZnCl₄, obtained by different crystal growing methods, has allowed us to determine the influence of growth defects on the incommensurate phase and on the lock-in transition of these samples. X-ray diffraction has allowed us to complete previous dielectric measurements realized on the same samples and to relate the crystalline quality to the evolution of the modulation as a function of the temperature. The principal influence of an increasing defect density seems to be a stronger pinning of the modulated phase and this induces a lower lock-in temperature and a wider hysteresis.     

加深光学速调管自发辐射谱调制的研究

相干谐波储存环自由电子激光的相干增强因子正比于光学速调管自发辐射谱调制率的平方,加深光学速调管自发辐射谱的调制是相干谐波储存环自由电子激光研究的重要一环.介绍在中国科学技术大学800MeV电子储存环上所进行的加深光学速调管自发辐射谱调制的研究工作,调制率已从0.236提高到了0.80,为相干谐波产生实验奠定了基础.     

利用O4测量去除车载差分吸收光谱测量污染源NO2排放通量计算中多次散射的影响

基于被动差分光学吸收光谱(DOAS)算法,使用车载被动DOAS技术在测量污染源排放通量时,由于云的多次散射影响,导致污染源排放通量的计算误差.特别对于像NO2这样的整层分布气体,由于低层云的出现造成多次散射增强使得NO2浓度显著升高,造成在计算污染源排放通量时产生较大误差.针对此问题,提出在车载DOAS污染源排放通量监...     

Temperature Change in the Electronic Spectra of an NH2(CH3)2CuCl3 Crystal in Phase Transitions

Based on data of the spectral studies of an NH₂(CH₃)₂CuCl₃ crystal, the presence of phase transitions of the first kind at temperatures T ₁ = 282.5 K and T ₂ = 245 K (in a cooling regime) is confirmed. Identification of the intraionic absorption bands of the Cu²⁺ ion and calculation of the parameters of the energy and space structure of the crystal are carried out. A decrease in the tetragonal distortion of the CuCl₅ polyhedron with decreasing the temperature is found. The empirical Urbach rule is observed to be fulfilled in the lowtemperature phases of the crystal.     

介质球掺杂导致的无序效应对光子晶体光学性能的影响

采用自组装法制备了聚苯乙烯(PS)微球三维光子晶体结构,通过在PS微球悬浮液中掺入不同浓度的二氧化硅大球,实现了光子晶体结构从有序向无序过程的转变。通过对这些样品的透射、反射进行测量和分析,发现无序效应对光子晶体的光子响应特性具有极大的影响,随着无序程度的增加,高频波段的透射率急剧下降,低频波段的法布里-珀罗振荡消失,光子带隙蓝移且逐渐消失;而在掺杂浓度为0.02%(质量分数)时,光子晶体带隙中心的最低透射率从10%下降到1%,且反射单峰随着探测角度的增大而分裂为双峰。这有助于基于介质球三维光子晶体沿Γ-L方向透射消光,促进其在新型光学器件领域的应用发展。     

光束束宽对自散焦介质中诱导光束聚焦的影响

影响自散焦介质中诱导光束聚焦过程的方程参量和初始条件共有5个，即两光束波长比(方程参量)、抽运光和信号光的初始振幅、两光束初始束宽比和两光束中心初始间距。通过数值计算讨论了初始束宽比在不同初始光束间距和波长比情况下对信号光聚焦过程的影响，得到了信号光聚焦效果的最佳初始参量条件。从而实现了对影响自散焦介质中诱导光束聚焦过程5个参量的完整详细研究。     

非即变相位共轭反馈对半导体激光器动态特性的影响

从四波混频产生相位共轭的物理原因出发,定义了相位共轭镜（PCM）的响应时间．建立起非即变相位共轭反馈条件下半导体激光器的外腔模型。以响应时间及频率失调为参变量,对其分岔及噪声等动态行为进行数值分析。结果表明,不考虑噪声影响时,增加相位共轭镜响应时间会使混沌带出现的次数和范围得到较大的抑制,当响应时间增大到1．5ns时,混沌带消失,半导体激光器保持稳定的单周期状态;考虑噪声影响后,随若响应时间的相对强度噪声（RIN）可减小几dB甚至十几dB,产生突变需要的反馈量也增大一个数量级以上,且其频谱的峰值向高频方向移动;另外,由于共轭反馈引起的频率失调低于半导体激光器激射频率3个数量级以上．它只对分岔特性有影响．对相对强度噪声的影响几乎为零。     

γ-辐照对纯Y_2SiO_5和Eu~(3+)∶Y_2SiO_5晶体光谱性能的影响

研究了γ-辐照前后纯Y2SiO5和Eu3+掺杂的Y2SiO5晶体吸收光谱的变化,辐照后,未退火和氢气退火的纯Y2SiO5晶体在260~270 nm和320 nm波段产生了附加吸收峰,分别是由F心和O-心的吸收引起的;经过空气退火的纯YSO晶体中,由于消除了氧空位,因此辐照后没有出现色心吸收峰。在Eu3+∶Y2SiO5晶体中,不但有相同的F心和O-心吸收峰,而且还有Eu2+离子在300 nm和390 nm的吸收峰。随着辐照剂量的增加,色心附加吸收峰增强。空气退火能减少Eu3+∶Y2SiO5晶体中的色心,而氢气退火能增加色心。