组合脉冲激光铝等离子体的数值模拟研究

为了获得组合脉冲激光诱导等离子体光谱性能增强的物理机制, 基于FLASH程序模拟计算了预脉冲参数对组合脉冲激光诱导的铝等离子体参数时空分布的影响, 获得了在不同预脉冲波长和不同预主脉冲延时下产生的铝等离子体电子温度、电子密度和烧蚀质量的空间演化规律。结果表明, 在预主脉冲总能量相同的情况下, 随着预脉冲波长从0.266μm变化到1.064μm, 高温环境氦气等离子体羽辉的空间范围从0.7cm增大到3.0cm, 但组合脉冲对靶材的烧蚀效率严重下降, 而铝等离子体的最大电子温度保持稳定; 此外, 组合脉冲的时间延迟低于100ns。该研究可为组合脉冲激光诱导击穿等离子体光谱增强技术提供理论参考。     

双预脉冲和弯曲靶对X射线激光输出特性的影响

为了探索低泵浦能量下得到X射线激光(XRL)并提高其输出强度的方法,对弯曲靶技术和双预脉冲技术进行了理论分析和数值模拟,模拟结果表明第二预脉冲与第一预脉冲间隔2 ns,主脉冲与第二预脉冲间隔5 ns时效果等离子体增益的时空特性曲线最好.随后在"星光Ⅱ"激光装置上进行了双预脉冲驱动类氖铬(J=0-1,3p-3s跃迁)XRL实验,得到了28.5 nm的单线X射线激光,结果表明在脉冲结构和泵浦总能量不变情况下XRL输出强度主要与第二预脉冲强度有关,实验结果很好地符合了数值模拟结果.     

激光诱导击穿锌等离子体的空间膨胀特性及能量依赖关系的研究

本文通过激光诱导击穿光谱技术研究了锌等离子 体在空间膨胀时其特性的演化,并研 究了等离子体产生对激光脉冲能量的依赖关系。在大气环境下将脉冲激光聚焦于锌金属靶表 面烧蚀并产生等离子体,采集等离子体膨胀方向不同距离处的时间分辨荧光光谱,确定等离 子体的电子温度及电子数密度参数,研究等离子体特性随空间膨胀距离及时间的演化关系。 然后改变激光脉冲能量,采集特定位置的锌等离子体荧光光谱,确定等离子体特征参数及其 时间演化特性对激光脉冲能量的依赖关系,研究激光脉冲能量对等离子体形成的影响。结果 表明,等离子体形成后其早期膨胀过程为超音速绝热膨胀,随等离子体空间膨胀距离的增加 电子温度先降低后升高,电子数密度先升高后降低。当延迟时间增加至2.2us时,随着空间 距离的增加,电子温度持续下降,电子数密度基本维持不变,此时超音速绝热过程消失。当 激光脉冲能量增加时,锌元素特征谱线强度逐渐饱和,电子数密度增加速率逐渐降低,等离 子体寿命持续增加。当激光脉冲能量低于100 mJ时,电子温度随激光 脉冲能量的增加而快速 上升。当激光脉冲能量高于100 mJ时,电子温度维持在 8500 K上下波动。因此,随着激光脉 冲能量的增加,等离子体屏蔽效应逐渐明显,脉冲激光与锌金属靶相互作用前期产生的等离 子体吸收激光脉冲能量维持自身的存在,最终导致仅有部分激光脉冲能量与金属发生相互作 用,使得谱线强度及电子温度的上升出现阈值。     

脉冲激光与脉冲GMAW复合焊接的动态交互行为

将连续激光、脉冲激光分别与脉冲GMAW(熔化极气体保护焊)进行复合,研究了不同复合焊接模式下激光离子体与电弧等离子体的动态交互行为。研究结果表明:与连续激光+脉冲GMAW复合焊接模式相比,脉冲激光+脉冲GMAW复合焊接模式可以在激光平均功率较小的情况下获得更大的熔深;在复合过程中,当激光脉冲峰值出现的时刻错开电流峰值的上升期时,这一瞬态时刻等离子体的急剧膨胀现象可以得到抑制,激光能量的传输可以得到改善。     

激光声特性与激光脉冲能量对应关系研究

分析了激光脉冲能量与激光声特性的对应关系.采用脉冲能量可调的Nd∶ YAG激光器产生激光声信号,利用水听器测量激光声信号.结果表明,激光脉冲能量在70～300mJ范围内变化时,随着激光脉冲能量的增加,激光声信号峰值声压具有线性增加的趋势,等离子体膨胀声波与空泡溃灭声波的时间间隔也相应增加,等离子体膨胀声波的峰值声压比空泡溃灭声波的峰值声压低,激光声信号的主频与脉冲能量的对应关系较弱.     

1064nm激光诱导等离子体开关控制355nm脉宽可调输出

为得到脉宽可控的355nm紫外脉冲激光输出,采用1064nm脉冲激光诱导等离子体开关技术,控制355nm激光脉冲宽度,在激光电离Cu小孔内壁表面及空气击穿共同作用下,获得了2.8ns～10ns的脉宽可调输出。讨论了1064nm单脉冲输出能量对脉宽压缩的影响,在无延时情况下得到了脉宽最短达2.8ns的脉冲激光输出。在此基础上,保持1064nm单脉冲输出能量不变,采用延时装置改变两光路间的光程差,以控制等离子体开关相对于355nm激光脉冲的形成时间,最终得到脉宽可调的脉冲激光输出。结果表明,等离子体开关结构简单、操作方便、适用范围广,是一种较好的脉冲整形手段。     

1064nm激光诱导等离子体开关控制355nm脉宽可调输出

为得到脉宽可控的355nm紫外脉冲激光输出,采用1064nm脉冲激光诱导等离子体开关技术,控制355nm激光脉冲宽度,在激光电离Cu小孔内壁表面及空气击穿共同作用下,获得了2.8ns～10ns的脉宽可调输出.讨论了1064nm单脉冲输出能量对脉宽压缩的影响,在无延时情况下得到了脉宽最短达2.8ns的脉冲激光输出.在此基础上,保持1064nm单脉冲输出能量不变,采用延时装置改变两光路间的光程差,以控制等离子体开关相对于355nm激光脉冲的形成时间,最终得到脉宽可调的脉冲激光输出.结果表明,等离子体开关结构简单、操作方便、适用范围广,是一种较好的脉冲整形手段.     

放电激励XeF(B→X)准分子激光器的高效率运转

在一台X射线预电离的XeF(B→X)准分子激光器中,我们应用磁开关隔离的预脉冲-主脉冲放电激励电路和磁脉冲压缩技术,研究了激光输出能量和转换效率对气体组份、总气压、电路参数和延迟时间的依赖关系,激光性能获得较大改进。当放电体积为0.11L,气体混合物(NF_3/Xe/Ne)的总气压为2.5×10~5 Pa时,激光输出能量345 mJ,总效率达3％。     

缓冲气压对CO2激光Al靶等离子体参量的影响

为了研究缓冲气压对激光等离子体参量的影响,利用CO2,激光烧蚀A1靶产生等离子体,缓冲气压变化范围为10-4Pa～2103Pa,激光脉冲能量为180mJ/脉冲,在局域热平衡和光学薄等离子体假设下,采用发射光谱法计算了等离子体的电子温度和电子密度,并研究了缓冲气压对这些参量的影响。结果表明,等离子体的电子温度和电子密度分别在1.05eV～2.47eV与1.951016cm-3～10.5 1016cm-3范围内,Al等离子体的电子温度随气压的增大而减少;低缓冲气压时,电子密度随气压增大而减小,当气压达到600Pa时,激光脉冲会击穿空气形成等离子体,电子密度又开始上升,当气压超过3000Pa时,空气等离子体会屏蔽激光脉冲能量,使到达靶面的激光能量急剧下降,Al原子的特征谱线也随之减弱而几乎消失。这一结果对理解缓冲气压对激光与物质相互作用过程的影响是有帮助的。     

声学法测量激光等离子体能量的研究

本文利用激光等离子体声波对高功率脉冲激光与材料相互作用过程进行了测量,首次得到了一定条件下几种材料的激光等离子体能量值。     

Preparation and Characterization of TaN ALD Precursors

High purity organic-tantalum precursors for thin film ALD TaN were synthesized and characterized.Vapor pressure and thermal stability of these precursors were studied.From the vapor pressure analysis,it was found that TBTEMT has a higher vapor pressure than any other published liquid TaN precursor,including TBTDET,TAITMATA,and IPTDET.Thermal stability of the alkyl groups on the precursors was investigated using a 1H NMR technique.The results indicated that the tertbutylimino group is the most stable group on TBTDET and TBTEMT as compared to the dialkylamido groups.Thermal stability of TaN precursors decreased in the following order:TBTDET ＞ PDMAT ＞ TBTEMT.In conclusion,precursor vapor pressure and thermal stability were tuned by making slight variations in the ligand sphere around the metal center.     

Curved crystal spectrometer for the measurement of X-ray lines from laser-produced plasmas

In order to diagnose the laser-produced plasmas, a focusing curved crystal spectrometer has been developed for measuring the X-ray lines radiated from a laser-produced plasmas. The design is based on the fact that the ray emitted from a source located at one focus of an ellipse will converge on the other focus by the reflection of the elliptical surface. The focal length and the eccentricity of the ellipse are 1350 mm and 0.9586, respectively. The spectrometer can be used to measure the X- ray lines in the wavelength range of 0.2-0.37 nm, and a LiF crystal （200） （2d = 0.4027 nm） is used as dispersive element covering Bragg angle from 30° to 67.5°. The spectrometer was tested on Shengnang- Ⅱ which can deliver laser energy of 60-80 J/pulse and the laser wavelength is 0.35 μm. Photographs of spectra including the 1 s2p ^1P1-1s^2 ^1S0 resonance line（w）, the 1s2p ^3P2-1s^2 1S0 magnetic quadrupole line（x）, the 1s2p ^3P1-1 s^2 ^1S0 intercombination lines（y）, the 1 s2p ^3S~1-1 s^2 ^1S0 forbidden line（z） in helium-like Ti Ⅹ Ⅺ and the 1 s2s2p ^2P3/2-1 s622s ^2S1/2 line（q） in lithium-like Ti Ⅹ Ⅹhave been recorded with a X-ray CCD camera. The experimental result shows that the wavelength resolution（λ/△ 2） is above 1000 and the elliptical crystal spectrometer is suitable for X-ray spectroscopy.     

Electronic Structure of Semiconductor Nanocrystals

This paper reviews our recent development of the use of the large-scale pseudopotential method to calculate the electronic structure of semiconductor nanocrystals, such as quantum dots and wires, which often contain tens of thousands of atoms. The calculated size-dependent exciton energies and absorption spectra of quantum dots and wires are in good agreement with experiments. We show that the electronic structure of a nanocrystal can be tuned not only by its size,but also by its shape. Finally,we show that defect properties in quantum dots can be significantly different from those in bulk semiconductors.     

Critical Stage Rule-Based Real Time Dispatch（RTD）System in Highly-Mixed-Products （HMP） FAB

An improving utilization and efficiency of critical equipments in semiconductor wafer fabrication facilities are concerned. Semiconductor manufacturing FAB is one of the most complicated and cost sensitive environments. A good dispatching tool will make big difference in equipment utilization and FAB output as a whole. The equipment in this paper is In-Line DUV Scanner. There are many factors impacting utilization and output on this equipment group. In HMP environment one of the issues is changing of reticule in this area and idle counts due to load unbalance between equipments. Here we'll introduce a rule-based RTD system which aiming at decreasing the number of recipe change and idle counts among a group of scanner equipment in a high-mixed-products FAB.     

GaAsSb/InAlAs PA DHBTs Grown by Production MBE

The epi material growth of GaAsSb based DHBTs with InAlAs emitters are investigated using a 4 × 100mm multi-wafer production Riber 49 MBE reactor fully equipped with real-time in-situ sensors including an absorption band edge spectroscope and an optical-based flux monitor. The state-of-the-art hole mobilities are obtained from 100nm thick carbon-doped GaAsSb. A Sb composition variation of less than ± 0.1 atomic percent across a 4 × 100mm platen configuration has been achieved. The large area InAlAs/GaAsSb/InP DHBT device demonstrates excellent DC characteristics,such as BVCEO＞6V and a DC current gain of 45 at 1kA/cm2 for an emitter size of 50μm × 50μm. The devices have a 40nm thick GaAsSb base with p-doping of 4. 5 × 1019cm-3 . Devices with an emitter size of 4μm × 30μm have a current gain variation less than 2% across the fully processed 100mm wafer. ft and fmax are over 50GHz,with a power efficiency of 50% ,which are comparable to standard power GaAs HBT results. These results demonstrate the potential application of GaAsSb/InP DHBT for power amplifiers and the feasibility of multi-wafer MBE for mass production of GaAsSb-based HBTs.     

Noise character analysis and the restraint of self-pulsation laser diodes

We calculate the Langevin noise sources of self-pulsation laser diodes, analyze the effects of active region noise and saturable-absorption region noise on the power fluctuation as well as period fluctuation, and propose a novel method to restrain the noise effects. A visible SIMULINK model is established to simulate the system, The results indicate that the effects of noise in absorption region can be ignored; that with the increase of DC injecting current, the noise effects enhance power jitter, and nevertheless, the period jitter is decreased; and that with external sinusoidal current modulating the self-pulsation laser diode, the noise-induced power jitter and period jitter can be suppressed greatly. This work is valuable for clock recovery in all-optical network.     

High-quality single-crystal CdSe nanoribbons and their optical properties

Large-scale synthesis of single-crystal CdSe nanoribbons is achieved by a modified thermal evaporation method, in which two-step-thermal-evaporation is used to control CdSe sources＇ evaporation. The synthesized CdSe nanoribbons are usually several micrometers in width, 50 nm in thickness, and tens to several hundred micrometers in length. Studies have shown that high-quality CdSe nanoribbons with regular shapes can be obtained by this method. Room-temperature photolumines-cence indicates that the lasing emission at 710 nm has been observed under optical pumping （266 nm） at power densities of 25-153 kW/cm^2. The full width half maximum （FWHM） of the lasing mode is 0.67 nm     

Propagation of hermite-cosh-gaussian beams passing through ABCD optical system with an annular aperture

By using the expansion of the aperture function into a finte sum of complex Gaussian functions, the corresponding analytical expressions of Hermite-cosh-Gaussian beams passing through annular apertured paraxially and symmetrically optical systems written in terms of ABCD matrix were derived, and they could reduce to the cases with squared aperture. In a similar way, the corresponding analytical expressions of cosh-Gaussian beams through annular apertured ABCD matrix were also given. The method could save more calculation time than that by using the diffraction integral formula directly.     

Influence of polarization extinction ratio on distributed polarization coupling detection

Distributed polarization coupling in polarization-maintaining fibers can be detected by using a white light Michelson interferometer. This technique usually requires that only one polarization mode is excited. However, in practical measurement, the injection polarization direction could not be exactly aligned to one of the principal axes of the PMF, so the influence of the polarization extinction ratio should be considered. Based on the polarization coupling theory, the influence of the incident polarization extinction on the measurement result is evaluated and analyzed, and a method for distributed polarization coupling detection is developed when both two orthogonal eigenmodes are excited.     

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正Communications—VLSI Researches and industries of telecommunications have been growing rapidly in the last 20 years and will keep their high growing pace in the next decade.The involved researches and developments cover mobile communications,highway and last-mile broadband communication,domain specific communications,and emerging D2D M2M communications.Radio communication steps into its