YAG晶体色心的EPR谱

本文描述了8种YAG样品的室温和77K的EPR谱.从这些谱的参数与光谱的实验数据对照,认为晶体中有三种顺磁性的色心,其中g～2.00和g～1.98两条顺磁谱相应于光谱2×10~4cm~(-1)～3.4×10~4cm~(-1)的吸收带,为YAG基质晶体中的缺陷俘获一个电子构成的电子型缺陷中心;而 g～30.60的顺磁谱线与氧空位和掺杂的金属离子Mg~(2+) 、Cr~(3+)有关,推测为氧空位团或氧空位与金属离子构成的S>1/2的复合顺磁中心缺陷.YAG晶体随着在大气氛中高温退火,氧的进入和金属离子的掺入,造成电子和空间体积的不平衡,从而使晶体色心浓度加大.     

与铷（5^2S1／2）原子碰撞产生的铷7^2D态精细结构转移截面

本文报道使用蒸汽泡和两光子两步激发方法,测量原子激发态敏化荧光I_(3/2)~1和直接荧光I_(3/2)~2其与温度的关系,得到与基态(5~2S_(1/2)铷原子碰撞产生的铷7~2D_(5/2)→7~2D_(3/2)和7~2D_(3/2)→7~2D_(5/2)精细结构转移截面分别为:σ_(fs)=4.7×10~(-13)cm~2、σ_(fs)~’=7.0×10~(-13)cm~2;碰撞转移出7~2D双态的转移截面σ_(tr)(5/2)=0.62×10~(-13)cm~2.由计算的7~2D态几何截面σ_(geom)能够相对很好地描述σ_(fs)和σ_(fs)~’的数量级.     

α-Al_2O_3单晶中Fe~(3+)离子的电子顺磁共振

本文对α-Al_2O_3单晶体中Fe~(3+)离子在室温下,X波段进行了电子顺磁共振研究,发现Fe~(3+)离子实际上占据四种磁性不等价晶位。在同一氧离子层间的两种晶位上的Fe~(3+)离子具有相同的自旋哈密顿参量,而不同氧离子层间的晶位上的Fe~(3+)离子具有不同的自旋哈密顿参量,两种自旋哈密顿参量为:(1)g=2.001,g=2.003,D=1679×10~(-4)cm~(-1),|α|=237×10~(-4)cm~(-1),α—F=317×10~(-4)cm~(-1);(2)g=2.001,g=2.006,D=1660×10~(-4)cm~(-1),|α|=243×10~(-4)cm~(-1),α—F=338×10~(-4)cm~(-1)。     

CdH分子基态X~2∑~+和激发态A~2П光谱和寿命测量

采用一束激光为泵浦光另一束激光为探测光的方法,获得CdH分子A~2Π态和X~2∑~+态之间跃迁产生的具有转动结构的多个荧光谱和激发谱带.对荧光的时间分辨研究,给出A~2Π态寿命τ_0=59.5±2.3ns,对A~2Π(v=0)态Cd原子的碰撞猝灭截面为(1.31±0.03)×10~(-15)cm~2;X~2∑~+态寿命τ_0=61.0±4.6μs,引起X~2∑~+(v=0)态寿命衰减的碰撞截面为(1.1±0.1)×10~(-18)cm~2.     

进一步寻找磁单极子的实验进展

本文介绍了进一步寻找磁单极子的实验进展。目前没有新的磁单极子候选者被观测到。慢磁单极子的实验流强上限:速度在(10~(-4)-10~(-2))c范围内的观测,低于3.0×10~(-12)cm~(-2)sr~(-1)s~(-1);在(10~(-3)-10~(-2))c范围的观测,低于4.1×10~(-13)cm~(-2)sr~(-1)s~(-1)。     

三唑和环戊烯苯并菲衍生物盘状液晶分子的电荷传输性质

电荷传输是有机电子材料的重要性质. 根据Marcus理论模型, 电荷传输为电子-电子相互作用和电子-声子相互作用过程, 电子-声子相互作用耦合强度越大, 重组能越大, 不利于电荷传输. 电子-电子相互作用耦合强度越大, 电荷传输矩阵元越大, 有利于电荷传输. 对含1, 2, 4-三唑、1, 2, 3-三唑和1, 2, 3-三氮-2, 3环戊烯边链的苯并菲衍生物分子的电荷传输性质进行理论研究. 结果表明, 含1, 2, 3-三唑的苯并菲衍生物分子的空穴传输速率和电子传输速率相当, 速率常数为2× 10¹²s^-1. 含1, 2, 4-三唑的苯并菲衍生物分子的空穴传输速率常数为5× 10¹²s^-1, 约为电子传输速率常数的10倍. 含1, 2, 3-三氮-2, 3环戊烯的苯并菲衍生物分子的电子传输速率常数为3× 10¹²s^-1, 约为空穴传输速率常数的10倍. 目标分子的空穴传输或电子传输速率主要受传输矩阵元的影响, 即电子-电子相互作用耦合强度的大小决定传输速率的变化.     

中子辐照对熔融织构YBa_2Cu_3O_(7-δ)超导体磁学性能及微观组织的影响

本文研究了中子辐照对熔融织构生长(MTG)YBaCuO 超导样品磁学性能及微观组织的影响.采用了两种辐照剂量:2.3×10~(16)n/cm~2和1.16×10~(17)n/cm~2.通过比较辐照前后样品磁滞回线,发现临界电流密度明显提高,在77K、0.1T 磁场下,临界电流密度达到4.7×10~5A/cm~2,此辐照前样品的临界电流密度提高了几十倍.通过观察辐照前后不可逆线 T~*(H)的变化,发     

铁电单晶(K_xNa_(1-x))_(0.4)(Sr_yBa_(1-y))_(0.8)Nb_2O_6的光学性质和线性电光效应

本文介绍铁电单晶(K_xNa_(1-x))_(0.4)(Sr_yBa_(1-y))_(0.8)Nb_2O_6的光学性质和线性电光效应的测量。实验结果表明,这种晶体具有较大的光学双折射,透光范围由4000A到5.6μm。晶体具有低的线性电光调制的半波电压,其电光调制价值指数n_0~3·γ_c高达730×10~(-12)m/V,而激光损伤阈值为600MW/cm~2(4 pps),表明该晶体可作为较大功率激光调制使用的材料。     

氮化铝薄膜的红外吸收光谱和喇曼光谱的研究

本文报道用直流平面磁控溅射法在Si片上生长c轴高度择优取向AIN薄膜的光学特性.俄歇谱分析表明薄膜是高纯的.从红外吸收光谱上分析获得晶格振动纵、横模的频率分别为2.5×10~(13)HZ和1.8×10~(13)Hz.从喇曼光谱上分析获得AIN薄膜的光学声子频率为297、512、607、656、832cm~(-1).与几种已知的纤锌矿结构二元化合物的声子频率模式类比获得AIN的光学声子模式.进一步分析表明AIN是一种静电力大于原子间各向异性力的晶体,且声子的最高频率与r~(-3/2)N~(-1/2)成正比.     

熔融织构YBCO超导体磁化临界电流的各向异性

对烧结处理和熔融织构处理 Y_1Ba_2C_3Ox 超导体材料分别进行磁化曲线测量,结果表明熔融织构样品,其磁化强度明显地受外加磁场方向的影响,应用扩展的 Bean 模型,我们计算了沿晶体 ab 面和 C 轴方向的磁化临界电流密度,对于一长条样品,它们值分别为2.3 ×10~4A/cm~2(77K,1.2T),8.9×10~2A/cm~2(77K,1.2T).将两者的比值与前人的工作了比较.     

High-speed photorefraction at telecommunication wavelength 1.55 microm in Sn2P2S6:Te

We demonstrated for what is the first time to our knowledge photorefractive two-wave mixing in a bulk ferroelectric crystal using cw light at the telecommunication wavelength 1.55 microm. In the Te-doped ferroelectric semiconductor Sn2P2S6 with absorption constant <0.1 cm(-1) at 1.55 microm, grating recording times of 10 ms and a two-beam coupling gain of 2.8 cm(-1) have been measured at 350 mW power (intensity 440 W/cm(2)) without a necessity to apply an external electric field. With a moving grating technique, a maximal gain of 6.0 cm(-1) has been obtained.     

Low-temperature thermal fixing of holograms in photorefractive La(3)Ga(5)SiO(14):Pr(3+) crystal

Thermal fixing in a La(3)Ga (5)SiO (14):Pr (3+) photorefractive crystal is demonstrated all the way down to room temperature. This, to our knowledge, is the first report of such an effect in any photorefractive material. From the temperature dependence of the process the activation energy of the carriers involved in the fixing process is measured to be E(A)=0.89 eV . Further, an effective photorefractive charge density of (1.4+/-0.2)x10(16) cm (-3) and Debye screening length of (6.8+/-0.7)x10(-6) cm is measured.     

Photorefractive effect in the relaxor ferroelectric material 0.91Pb(Zn1/3Nb2/3)O3-0.09PbTiO3

The photorefractive effect in a nominally undoped 0.91Pb(Zn1/3Nb2/3)O3-0.09PbTiO3 single crystal is measured. We report what is, to our knowledge, the first observation of the photorefractive effect in Pb-based relaxor ferroelectric crystals. The crystal is grown by the flux solution method. Then it is cut into a 2 mm x 4 mm x 8 mm piece and electrically poled along the [111] direction. The coupling constant of the two-wave mixing is 17 cm(-1), and the normalized time constant under 1-W/cm(2) illumination is 12 s at a wave-length of 476 nm. The effective trap density is calculated as 5 x 10(16) cm(-3) from the Debye screening length under the assumption of Kukhtarev's band-transport model. The dominant carrier is identified to be holes from the direction of two-wave mixing energy transfer.     

In∶Nd∶LiNbO3晶体倍频性能的研究

在 LiNbO₃中掺进In₂O₃和Nd₂O₃, 以Czochralski技术生长了In∶Nd∶LiNO₃晶体. 通过光斑畸变法测得In∶Nd∶LiNbO₃晶体的光损伤阈值为1.98×104 W/cm², 比Nd∶LiNbO₃晶体的1.6×102 W/cm²高两个数量级以上;晶体吸收光谱的测试表明, In∶Nd∶LiNbO₃晶体的吸收边相对Nd∶LiNbO₃晶体发生紫移. 研究了In∶Nd∶LiNbO₃晶体的倍频性能, 结果表明, In∶Nd∶LiNbO₃晶体的相位匹配温度在室温附近, 倍频转换效率比Nd∶LiNbO₃晶体提高二倍.     

Photorefractive properties of paraelectric potassium lithium tantalate niobate crystal doped with iron

We report the successful growth of paraelectric potassium lithium tantalate niobate (KLTN) single crystal doped with iron. Detailed investigations have been made on the photorefractive properties of the as-grown crystal. The key parameters such as space-charge field, grating response time, photorefractive sensitivity and sign of the dominant charge carrier were obtained by two-wave mixing technique. 1.7 mm thick sample exhibits a high diffraction efficiency of 78% at the external field of 3.3 kV/cm and a sensitivity of 1.49 × 10⁻¹⁰E₀ cm²/J. The two-wave mixing gain coefficient increases linearly with external field, and reaches a large value of 19.4 cm⁻¹ at 4 kV/cm. Based on experimental results, iron is an effective dopant to KLTN which shows high diffraction efficiency and two-wave mixing gain coefficient.     

On the Electrode Damage and Current Densities of Carbon Arcs

Arc damage on carbon electrodes has been examined as a function of the charge passing through each arc in the range from 10-6 to 10-1 coloumb. Two forms of arcing damage were observed: that due to the so-called vapor arc, which has a very high current density (~6 × 107 A/cm2) and low erosion rate, and that due to the so-called thermionic arc with a lower current density (~2 × 103 A/cm2) and higher erosion rate. Unlike damage observed on metallic electrodes raised rims were not formed around the carbon craters. The vapor mode damage is compared with two known models of cathode erosion. Differences between the vapor and thermionic modes and the transition between them are discussed. A whitish-gray deposit observed on the arced electrodes appears to be a form of graphite.     

Flux-limited nonequilibrium electron energy transport in warm dense gold

An abrupt change in energy transport has been observed in femtosecond laser heated gold when the absorbed laser flux exceeds ~7×10(12) W/cm(2). Below this value, the absorbed flux is carried by ballistic motion of nonthermal electrons produced in interband excitation. Above this value energy transport appears to include ballistic transport by nonthermal electrons and heat diffusion by thermalized hot electrons. The ballistic component is limited to a flux of ~7×10(12) W/cm(2). This offers a unique benchmark for comparison with theory on nonequilibrium electron transport.     

Superior real-time holographic storage properties in doped potassium sodium strontium barium niobate crystal

We demonstrate superior holographic storage performance in a cobalt doped potassium sodium strontium barium niobate (Co:KNSBN) crystal that possesses a fast response time of 1.4 ms, a large photorefractive sensitivity of 13 x 10(-3) cm(3) J(-1) under a total writing intensity of 1 W/cm(2) , and high spatial resolution of 45 line pairs/mm. Reconstructed images with high fidelity have been obtained in real-time holographic storage. The dynamic properties of the index grating, the dependence of response time on writing intensity, and the dark decay of diffraction signal with increased writing intensity indicate that two species and shallow traps exist in Co:KNSBN crystal.     

High-frame-rate joint Fourier-transform correlator based on Sn(2)P(2)S(6) crystal

We present a joint Fourier-transform correlator working at a 10-kHz repetition rate. It is based on a photorefractive Sn(2)P(2)S(6) crystal operated in the pulsed direct band-to-band photoexcitation regime at a wavelength of 532 nm and a pulse length of 50 ns. The intersection of two plane waves with a total pulse fluence of 100muJ/cm(2) results in a buildup of thin dynamic holograms to a typical diffraction efficiency of 10(-4) in a time of ~1mus and decay again in less than 10mus . The correlator was tested by a fast image sequence generated by the pulsed readout of a holographic memory system. Successful correlation at a rate of 10 kHz has already been achieved for a pulse energy of only 200 nJ in the template images.     

Photorefractive effect of a novel conjugate polymer containing transition metal complex

The photorefractive effect (PR) of a novels σ-π alternating polymer having 2,2'-bipyridyl in the polymer backbone and their ruthenium complexes has been investigated. The ruthenium complex was used as the charge generator, the σ-π alternating polymer backbone as the charge transporting channel and second-order nonlinear (NLO) optical chromophore. The photorefractive properties were demonstrated by two-beam coupling (2BC), degenerated four-wave mixing (DFWM) and field-induced orientation birefringence at wavelength of 532 nm. This polymer shows a enhanced photorefractive effect due to the efficient photoinduced metal-to-ligand charge transfer (MLCT) inside the ruthenium complex. A net optical gain of about 22 cm^-1 and the diffraction efficiency about 10% were obtained at the external electric field of 30 V/μm. Received 21 December 1999 and Received in final form 7 July 2001