电光-GaAs主被动双调Q激光特性研究

为了研究调Q激光脉冲波型的对称性,利用电光调制和GaAs半导体饱和吸收体,实现了电光-GaAs主被动双调Q激光运转。与单一电光主动调Q或GaAs被动调Q激光对比,双调Q激光的脉冲宽度更窄、脉冲波型更对称,其脉冲宽度的压缩比大于40%。定义了一个对称因子来描述脉冲波型的对称性,对称性的改善优于10%。在平面波近似下,给出了双调Q激光运转的耦合方程组,数值求解方程组得到的理论值与实验结果相符。     

CdTe电光调频晶体用于电光调Q研究

本文研究了CdTe电光调Q晶体及电光调频晶体的调制特性,报道了采用 CdTe电光调频晶体进行电光调 Q的光栅选支射频激励波导 CO2激光器,调 Q激光脉冲重复频率 1Hz～10 kHz可调,在 10 kHz重复频率时,获得激光脉冲峰值功率为 300 W,脉冲宽度为 150 ns.     

输出可调的电光调Q射频激励波导CO_2激光器的研究

研究了输出可调的光栅选支电光调Q射频激励波导CO2 激光器 ,可以通过调节电光晶体上的电压来调节调Q激光脉冲峰值功率、脉冲宽度、脉冲建立时间 ,理论分析与实验结果一致。同时采用另外一种激光器结构提高了激光输出功率。     

巨脉冲红宝石激光器的若干问题

一、引言 在激光脉冲全息摄影、等离子体诊断、人造卫星测距等方面的应用中,巨脉冲红宝石激光器是一个不可缺少的光源。而且,这类应用对红宝石激光器的输出功率、相干长度、束散角等都有一定的要求。本文讨论了巨脉冲红宝石激光器的若干问题:电光调Q、染料调Q以及电光-染料双调Q红宝石激光的相干长度;电光调Q的最佳工作条件以及红宝石棒的功率破坏等,这对于红宝石激光器的性能及应用具有实际意义。     

1.3414μm Nd:YAlO3电光Q开关脉冲激光器

本文介绍了一种用LiNb％晶体作为电光Q开关晶体的闪光灯泵浦1．3414μm Nd：YAlO3，电光调Q脉冲激光器，实验得到了脉宽45ns、输出能量312mJ的巨脉冲激光输出。     

Nd^3＋：YAG固体激光器电光调Q激光脉冲的时域分析

Nd^3＋：YAG固体激光器多元激光精密同步合成技术是实现大能量、高峰值功率脉冲激光输出的重要途径。其关键技术是对Nd^3＋：YAG固体激光器电光调Q进行精密光电控制。通过对Nd^3＋：YAG固体激光器电光调Q理论分析和仿真，得到单元激光器不同控制参数下的输出特性，经电光调Q专题试验验证，脉冲激光输出波形与仿真结果相吻合，达到预期效果。在此基础上提出了激光精密同步合成的技术条件和可行性。     

高重复频率电光调Q全固态激光器研究进展

高重复频率窄脉宽全固态激光器在激光加工领域以及空间激光通信、激光雷达、激光测距等空间应用领域都具有巨大的市场需求和广阔的应用前景.利用电光调Q方式可以获得窄脉宽、大能量激光脉冲输出,且具有良好的稳定性.近年来,随着新型电光晶体的出现,电光调Q开关的工作重复频率得到了显著的提高.主要综述高重复频率电光调Q全固态激光器在高速Q开关性能及激光输出方面的研究进展,并简要报道了研究小组在该研究领域取得的最新实验结果.     

光栅选支电光调Q射频激励波导CO_2激光器研究

本文在理论和实验上研究了光栅选支电光调 Q射频波导 CO2 激光器。调 Q激光脉冲重复频率 1Hz～ 10 k Hz可调 ,在 10 k Hz重复频率时 ,获得激光脉冲峰值功率为 15 0 W,脉冲宽度为 180 ns     

Nd3+:YAG固体激光器电光调Q激光脉冲的时域分析

Nd3+:YAG固体激光器多元激光精密同步合成技术是实现大能量、高峰值功率脉冲激光输出的重要途径.由于单元激光器为电光调Q体制固体激光器,脉宽10 ns量级,要实现时域上精密合成,其关键技术是在激光脉冲精密测时的前提下对Nd3+:YAG固体激光器电光调Q进行精密光电控制.通过对Nd3+:YAG固体激光器电光调Q激光脉冲建立机制的理论分析和仿真,得到单元激光器在不同控制参数下的输出特性.试验结果表明:脉冲激光输出波形与仿真结果相吻合,达到预期效果.在此基础上提出了激光精密同步合成的技术条件和可行性,开展了三单元的激光精密同步合成试验验证,经测试合成同步精度达到±1 ns,合成效率90%以上.     

通频带宽对脉冲激光波形测量的影响

在理论上分析了电光调QCO2激光脉冲经过不同通频带宽的测量系统时产生的波形失真情况,并且得出了通频带宽对测量波形影响的规律,同时在实验上研究了电光调Q射频激励波导CO2激光脉冲经过一定通频带宽的测量系统时,激光脉冲波形的失真情况,实验结果与理论分析一致。     

Growth and structure of wide-gap insulator films on SrTiO3

Wide-gap insulator films, CaZrO₃, CaHfO₃, LaGaO₃, and NdGaO₃, were grown on SrTiO₃(1 0 0) substrates with the aim of obtaining a gate insulator for epitaxial oxide devices. We show that CaZrO₃ and CaHfO₃ films were epitaxial and had a multi-domain in-plane structure due to their highly distorted perovskite structure. Most of the LaGaO₃ and NdGaO₃ films were polycrystalline, and therefore showed relatively high leak currents. CaHfO₃ had the best crystallinity among these four materials.     

Structure of organometallic chemical vapor deposited BaTiO3 thin films on LaAIO3

BaTiO₃ thin films grown on LaA1O₃ by organometallic chemical vapor deposition were characterized with cross-sectional high resolution transmission electron microscopy. Epitaxy was confirmed for the films grown on (100) oriented substrates. The films displayed an aaxis orientation. The interface between the film and substrate was nearly atomically abrupt. Partial relaxation of the films was observed as a result of misfit dislocation formation.     

Ca3Y2(Si3O9)2:Tb3+绿色荧光粉的光谱特性

采用高温固相法制备了Ca₃Y₂(Si₃O₉)₂: Tb³⁺绿色荧光粉,研究了材料的光学性能。X 射线衍射(XRD)结果显示,掺杂少量的Tb³⁺,并未影响Ca₃Y₂(Si₃O₉)₂材料 的晶相结构。Ca₃Y₂(Si₃O₉)₂:Tb³⁺ 荧光粉的激发光谱由较强的4f^75d1宽带吸收(200～300 nm )和较弱的4f-4f电子跃迁吸收 (300～500 nm)构成,主激发峰位于236nm。取波长分别为236、376和482nm的光 作为激发源时,发现样品的主发射峰均位于544 nm,对应Tb³⁺的⁵D 4→⁷F₅跃迁发射。以236nm 紫外光作为激发源,监测544nm主发射峰,随Tb³⁺浓度 的增大,Ca₃Y₂(Si ₃O₉)₂:Tb³⁺的荧光寿命逐渐减小,但在实验范围内并未出现浓度猝灭现象。     

Formation of secondary phases during crystal growth of Pb5Ge3O11

Studies of secondary phases formed during the Czochralski growth of lead germanate crystals (Pb₅Ge₃O₁₁) show that these phases form inclusions in the crystal, thereby reducing its optical quality, and can also cause twinning and cracking. Results of differential thermal analysis, energy dispersive X-ray fluorescence analysis, and X-ray diffraction studies of secondary phases are presented. The narrow stability range for Pb₅Ge₃O₁₁ shown in the phase diagram, the thermal instability of this compound, and its pronounced supercooling during crystallization suggest that equilibrium conditions are difficult to sustain and that other compounds of the PbO-GeO₂ family may form, although Pb₅Ge3O₁₁ is melting congruently. It is shown that Pb₃GeO₅ and PbGeO₃, which are both reported to melt congruently, can crystallize during the growth of Pb₅Ge₃O₁₁ forming inclusions in the crystal. The successful synthesis of these three compounds is reported. The compound Pb₃Ge₂O₇, reported in the literature, is identified as a mixture of Pb₅Ge₃O₁₁ and PbGeO₃. Experimental conditions are presented for growing single phase Pb₅Ge₃O₁₁ crystals of uniform composition and high optical quality. This paper is based on a presentation at the Conference on Preparation and Properies of Electronic Materials, Princeton, N. J., August 1975.     

LaNiO3 and Cu3Ge contacts to YBa2Cu3O7-x films

Metallization of high-T_c superconductors using low resistivity metal oxides and Cu-Ge alloys has been investigated on high quality pulsed laser deposited epitaxial YBa₂Cu₃O_7-x (YBCO) films. Epitaxial LaNiO₃ (LNO) thin films have been grown on YBCO films at 700°C using pulsed laser deposition. The specific resistivity of LNO was measured to be 50 μΩ-cm at 300K which decreases to 19 μΩ-cm at 100K indicating good metallicity of the LNO films. The contact resistance of LNO-YBCO thin film interface was found to be reasonably low (of the order of 10^-4Ω-cm² at 77K) which suggests that the interface formed between the two films is quite clean and LNO can emerge as a promising metal electrode-material to YBCO films. A preliminary investigation related to the compatibility of Cu₃Ge alloy as a contact metallization material to YBCO films is discussed. The usage of other oxide based low resistivity materials such as SrRuO₃ (SRO) and SrVO₃ (SVO) for metallization of high-T_c YBCO superconductor films is also discussed.     

Transport properties of thermoelectric materials for coolers

The Seebeck coefficient, thermal conductivity, electrical conductivity and Hall coefficient of cooler grade, p-and n-type ternary alloys of Bi₂Te₃-Sb₂Te₃-Sb₂Se₃ were measured between 10 and 300 K. Between 300 K and about 150 K the temperature dependence of the transport properties can be explained by assuming nondegeneracy and a lattice scattering mechanism. The difference between the temperature dependence of the Hall effect in n-and p-type alloys can be explained by the presence of sub-bands of light and heavy holes in the valence band of p-type alloys.     

The effect of Tl2Te3 on the properties of the solid solution (Sb2Te3)0.75.(Bi2Te3)0.25

The effect on transport properties of the addition of 0.5-5% Tl₂Te₃ to p-type solid solutions of antimony and bismuth tellurides was studied. It was found that the addition of Tl₂Te₃ caused a lessening of the increase of hole concentration as low temperatures were approached, resulting in a slower decrease of the Seebeck coefficient with a decrease in temperature. In partial fulfillment of M.Sc. degree, Hebrew University, Jerusalem. Permanent address, Dept. of Inorganic and Analytical Chemistry, Hebrew University, Jerusalem.     

Formation of aluminum oxide films from aluminum hexafluoroacetylacetonate at 350–450° c

A study of the thermally activated decomposition of Al(hfa)₃ (aluminum hexafluoroacetylacetonate) from the gas phase to form Al₂O₃ on silicon substrates is reported. The decomposition process was carried out in an open tube atmospheric pressure reactor in either argon or oxygen/argon mixtures in the temperature range, 350–450° C. The chemical vapor deposition process resulted in the formation of aluminum oxide films in all instances. The dielectric strength of Al/Al₂O₃/Si capacitors which received a post-metal anneal, but did not receive a high temperature annealing treatment, with aluminum oxide films prepared from Al(hfa)₃ in argon, was found to be in the range 2–6 MV/cm. The difference between the flatband voltage of the MOS structures and the metal-silicon work function difference was positive, indicative of a net negative oxide charge with a density of approximately 3 × 10¹¹ – 3 × 10¹² cm^-2, assuming the charge is located at the oxide-silicon interface. Decomposition of Al(hfa)₃ was also carried out in oxygen/argon mixtures with the oxygen concentration in the range 10–60 vol %. This process led to the deposition of aluminum oxide films with breakdown fields in the range 8–9 MV/cm. However, the flatband voltages of the Al/Al₂O₃/Si capacitors were even more positive than those obtained with Al₂O₃ formed in pure argon. High temperature (800–1000° C) oxygen or nitrogen annealing treatments of alumina films deposited in either argon or oxygen/argon mixtures were evaluated from the point of view of their influence on the oxide film properties. In particular, an annealing process in oxygen at 1000° C for 15 min was found to result in a reduction of the net negative oxide charge, and an improvement of the dielectric strength of films deposited in argon. Films formed in oxygen/argon mixtures did not change appreciably following oxygen annealing, as far as breakdown fields are concerned, but the oxide net negative charge was reduced. As in an earlier study by the authors, of copper film deposition from Cu(hfa)₂, it was found that essentially carbon free films could be obtained under appropriate conditions.     

Excellent performance of gas sensor based on In2O3-Fe2O3 nanotubes

In₂O₃-Fe₂O₃ nanotubes are synthesized by an electrospinning method. The as-synthesized materials are characterized by scanning electron microscope and X-ray powder diffraction. The gas sensing results show that In₂O₃-Fe₂O₃ nanotubes exhibit excellent sensing properties to acetone and formaldehyde at different operating temperatures. The responses of gas sensors based on In₂O₃-Fe₂O₃ nanotubes to 100 ppm acetone and 100 ppm formaldehyde are 25 (240℃) and 15 (260℃), and the response/recovery times are 3/7 s and 4/7 s, respectively. The responses of In₂O₃-Fe₂O₃ nanotubes to 1 ppm acetone (240℃) and formaldehyde (260℃) are 3.5 and 1.8, respectively. Moreover, the gas sensor based on In₂O₃-Fe₂O₃ nanotubes also possesses an excellent selectivity to acetone and formaldehyde.     

LaAlO3SrTiO3界面导电性的近场成像

铝酸镧/钛酸锶(LaALO3/SrTiO3)异质界面被发现具有二维导电性并呈现出其他一些有趣的呈展现象.而此前, LaAlO3/SrTiO3异质界面的导电性主要都是通过电学方法进行表征.这里作者首次提出利用散射式扫描近场光学显微镜 (s-SNOM) 对LaAlO3/SrTiO3界面的导电性进行空间成像, 这为研究过渡金属氧化物异质界面体系的物理现象提供了一个新的手段.