Influence of 3A molecular sieve to tetrahydrofuran(THF) hydrate formation

Visual observation of the THF hydrate formation process in the presence of a 3A molecular sieve has been made at normal atmosphere and below a temperature of zero by microscopy. The results indicate that a 3A molecular sieve can induce the nucleation of the THF hydrate and promote the THF hydrate growth. With the existence of a 3A molecular sieve, the growth rate of THF hydrate is between 0.01 and 0.05 mu m/s. In comparison with the system without any 3A molecular sieve, the growth rate increases about 4 nm/s. After the THF hydrate grows into megacryst, the crystals will recombine and partially change under the same condition.

ZnO thin film photoconductive ultraviolet detector with fast photoresponse

C-axis preferred oriented ZnO thin films were prepared on quartz substrates by RF sputtering. Photoconductive ultraviolet detector with planar interdigital electrodes was fabricated on ZnO thin film by the lift off technique. Linear I-V characteristic was observed under dark or 365 nm UV light illumination and has obvious difference. The photoresponsivity of 365 nm at 5 V bias is 18 A/W. The response time measure set mainly contains KrF excimer laser with the pulse width of 30 ns and the oscillograph with the bandwidth of 200 MHz. The result shows fast photoresponse with a rise time of 100 ns and fall time of 1.5 mu s. (c) 2005 Elsevier B.V. All rights reserved.

Harmonic mode-locked ytterbium-doped fibre ring laser

We demonstrate a harmonic mode-locked ytterbium-doped fibre ring laser, which consists of a polarization-sensitive isolator, two polarization controllers, two 976 nm laser diodes as the pump source and a two-segment ytterbium-doped fibre. Utilizing an additive pulse mode-locked technique based on nonlinear polarization evolution, the ytterbium-doped fibre laser can operate in mode-locked state by adjusting the position of polarization controllers. The cavity fundamental repetition rate is 23.78 MHz. We also observe the second- and third-harmonic mode locking in the normal dispersion region, and their repetition rates are 47.66 MHz and 71.56 MHz, respectively. Over-driving of the saturable absorber in the harmonic mode-locking pulse is analysed and discussed in detail.

Characteristic of the ultrawideband electromagnetic radiation generated by PCSS

A novel ultra-wideband electromagnetic pulse generating method based on the photoconductive semiconductor switches (PCSS) is presented. Gallium arsenide is used to develop the PCSS for an ultrashort electromagnetic pulse source. The pulse generated by such PCSS is within picosecond (ps) time scale, and can yield power pulse with an voltage over 10 kV. The experimental results show that the pulses are stable, with the peak-peak amplitude change of 6% and the time jitter within several picoseconds. The radiations of the PCSS triggered by the picosecond laser and fenitosecond laser pulse series illustrate that the electromagnetic pulses would have high repetition of more than 80 MHz and frequency bandwidth of DC-6 GHz. The radiations of "lock-on " mode of the PCSS are also analyzed here. (c) 2007 Wiley Periodicals, Inc.

Research on the ultrafast fluorescence property of thylakoid membranes of the wild-type and mutant rice

A high yielding rice variety mutant (Oryza sativa L., Zhenhui 249) with low chlorophyll b (Chl b) has been discovered in natural fields. It has a quality character controlled by a pair of recessive genes (nuclear gene). The partial loss of Chl b in content affects the efficiency of light harvest in a light harvest complex (LHC), thus producing the difference of the exciting energy transfer and the efficiency of photochemistry conversion between the mutant and wild-type rice in photosynthetic unit. The efficiency of utilizing light energy is higher in the mutant than that in the wildtype rice relatively. For further discussion of the above-mentioned difference and learning about the mechanism of the increase in the photochemical efficiency of the mutant, the pico-second resolution fluorescence spectrum measurement with delay-frame-scanning single photon counting technique is adopted. Thylakoid membranes of the mutant and the wild-type rice are excited by an Ar+ laser with a pulse width of 120 ps, repetition rate of 4 MHz and wavelength of 514 nm. Compared with the time and spectrum property of exciting fluorescence, conclusions of those ultrafast dynamic experiments are: 1) The speeds of the exciting energy transferred in photo-system I are faster than that in photo-system II in both samples. 2) The speeds of the exciting energy transfer of mutant sample are faster than those of the wildtype. This might be one of the major reasons why the efficiency of photosynthesis is higher in mutant than that in the wild-type rice.

Non-collinear CPOPA seeded by an Yb3+-doped self-starting passive mode-locked fiber laser

Using a home-made seed at 1053 nm from a Yb3+-doped passively mode-locked fiber laser of 1.5 nJ/pulse, 362 ps pulse duration with a repetition rate of 3.842 MHz, a compact, low cost, stable and excellent beam quality non-collinear chirped pulse optical parametric amplifier omitting the bulky pulse stretcher has been demonstrated. A gain higher than 4.0 x 10(6), single pulse energy exceeding 6 mJ with fluctuations less than 2% rms, 14 nm amplified signal spectrum and recompressed pulse duration of 525 fs are achieved. This provides a novel and simple amplification scheme. (c) 2007 Optical Society of America.

Eye-safe, high-energy, single-mode all-fiber laser with widely tunable repetition rate

We present a novel high-energy, single-mode, all-fiber-based master-oscillator-power-amplifier (MOPA) laser system operating in the C-band with 3.3-ns pulses and a very widely tunable repetition rate, ranging from 30 kHz to 50 MHz. The laser with a maximum pulse energy of 25 mu J and a repetition rate of 30 kHz is obtained at, a wavelength of 1548 nm by using a double-clad, single-mode, Er:Yb co-doped fiber power amplifier.

Environmentally stable ytterbium figure-of-eight fiber laser producing 177-fs pulses

Pulses of 177 fs and 1035 nm, with average power of 1.2 mW, have been generated directly from a passively mode-locked Yb-doped figure-of-eight fiber laser, with a nonlinear optical loop mirror for mode-locking and pairs of diffraction gratings for intracavity dispersion compensation. To our knowledge, these are the shortest pulses ever to come from a passively mode-locked Yb-doped figure-of-eight fiber laser. This represents a 5-fold reduction in pulse duration compared with that of previously reported passively mode-locked Yb-doped figure-of-eight fiber lasers. Stable pulse trains are produced at the fundamental repetition rate of the resonator, 24.0 MHz. (c) 2007 Elsevier B.V. All rights reserved.

Synthesis of novel hexagon SnO2 nanosheets in ethanol/water solution by hydrothermal process

The novel hexagon SnO2 nanosheets are successfully synthesized in ethanol/water solution by hydrothermal process. The samples are characterized by X-ray diffraction (XRD), infrared ray (IR) and transmission electron microscopy (TEM). By changing the reaction conditions, the size and the morphology can be controlled. Comparison experiments show that when the temperature increased from 140 degrees C to 180 degrees C, the edge length of the hexagon nanoparticles increases from 300-450 nm to 700-900 nm. On the other hand, by adjusting the ratios of water to ethanol from 2 to 0.5, SnO2 nanoparticles with different morphologies of triangle and sphere are obtained. When the concentration of NaOH is increased from 0.15 M to 0.30 M, a hollow ring structure can be obtained. (c) 2006 Elsevier B.V. All rights reserved.

稀土锰氧化物和双钙钛矿氧化物的合成及电磁性能研究

本文对钙钛矿锰氧化物La0.67Sr0.33MnO3、La0.67Sr0.33Mn1-xFexO3和双钙钛矿氧化物Sr2－xLaxMnMoO6、Sr2－xLaxMnWO6和Sr2(Ni，Co)WO6的结构、磁性和磁电阻效应进行了系统地研究。 利用溶胶-凝胶方法制得La0.67Sr0.33MnO3粉体，通过不同的烧结温度，可以对样品的微观结构进行调控。其中，晶界的状态对自旋电子的输运产生了明显的影响。900℃和1300℃烧结的样品，都出现了远低于居里温度的金属－半导体导电行为转变，表明自旋电子的传输不仅与晶粒的大小有关，而且与晶界状态密切联系。合适的烧结条件，可以得到大的，使用温区较宽的磁电阻效应。 在La0.67Sr0.33Mn1-xFexO3(0≤x≤0.2)体系中，Fe3＋的掺入没有明显改变La0.67Sr0.33MnO3的结构和晶胞参数，但却极大地降低了样品的居里温度。在x≥0.08时同样出现了低于居里温度的金属－半导体导电行为转变，这是由体系的铁磁态磁不均匀性导致的。电子顺磁共振研究表明，La0.67Sr0.33Mn1-xFexO3(0≤x≤0.20)的EPR谱中峰对峰宽（ΔHpp）在Tmin前后两种温区的线宽展宽机制不同。随着掺杂量的增加，在Tmin处的线宽逐渐变宽并且出现低场顺磁信号。x=0.20的样品，低场顺磁信号在380K左右开始衰减，与La0.67Sr0.33MnO3的顺磁信号具有类似的行为。我们利用相分离模型对系列样品的电子顺磁共振信号的变化规律进行了解释。 在Sr2－xLaxMnMoO6 (0≤x≤1)系列样品中，所有的样品都具有双钙钛矿有序结构。磁化强度、居里温度随掺杂量的增加而增大，但都存在磁受挫行为。在5T的外场下磁化强度依然没有饱和，实际测得的磁矩远远小于理论预测的结果。在低掺杂状态下出现分步磁化。La3+的掺入，不仅改变了体系电子能带的状况，而且极大的改变了体系的结构因素，两者竞争的结果，使体系的电磁性能产生了复杂的变化。

三联吡啶类过渡金属配合物的合成与光电性能

经过分步配位，得到以对苯乙烯撑为桥的双核2,2΄:6΄,2΄΄-三联吡啶钌配合物。这类配合物在室温下在490nm左右存在强的金属-配体电荷转移（MLCT）的吸收峰。在77K时，表现出强的红光发射（639-641nm）。双核配合物中基于中心离子钌的可逆的氧化电位在+1.25eV左右，基于三联吡啶的第一还原电位位于-1.15eV左右，两个核表现出对等的氧化还原性质。合成了叔丁基、己氧基、咔唑、二苯胺以及N-苯基萘胺取代的4΄-苯基-2,2′:6′,2″-三联吡啶（ptpy）衍生物配体与锌和镉形成的系列配合物。通过配体的修饰，配合物的发光颜色从紫色（392nm/397nm）调节到橙红色（604nm/602nm）。荧光发射表现出对溶剂极性的不同程度的依赖性。随着D-A结构趋于明显，配合物溶剂化效应表现得更强烈。电致发光器件研究表明，锌系列配合物的电致发光峰分别位于552nm、600nm和609nm，电流效率分别为5.28cd/A、2.38cd/A和2.00cd/A，亮度最高达到了2249cd/m2。合成了以苯撑和芴的齐聚物为桥的含双三联吡啶的配体，并在过渡金属锌或镉离子的诱导作用下，在温和的条件下获得一系列配位聚合物。其在二甲基甲酰胺溶液中的荧光量子效率最高达到0.41。金属离子的配位对提高光致发光的荧光量子效率的作用是积极的。这些配位聚合物的荧光发射大都在蓝光区（434-455nm）。芴单元的数目对最终聚合物的发光光谱具有一定影响，随着共轭单元的增长，发光峰位发生红移。电致发光器件性能研究表明，电致发光颜色则集中在黄绿光（531nm-560nm）范围。合成了2-(2-吡啶)喹啉衍生物一类配体，并考察了其与锌和镉的配位能力和配位方式。得到的配合物为五配位的配合物，其中两个配体和一个氯离子参与配位。咔唑和二苯胺在喹啉环6-位的引入，不仅较大范围的调节了该类配合物的发光颜色，而且获得了效率较高的红光发射(623nm，638nm)。电致发光器件表征得到了比较纯正的红光发射（648nm，CIE（0.63，0.36）），最大功率效率为0.01 lm/W。