连续波DF/HF化学激光器环形喷管与线形喷管的对比

环形喷管阵列主要用于环柱型化学激光器,它可以分为两种构型:直喉道型和圆喉道型。二者都可以由线性喷管阵列变换得到。在变换前后保持相同的增益区体积的前提下,环形喷管阵列的横向尺寸将减小为线性喷管阵列的1/π倍,这将更有利于激光器的紧凑化设计。由于圆喉道型环形喷管阵列相对直喉道型更具实用价值,通过三维的数值模拟,比较了圆喉道型环形喷管单元和线形喷管单元的流场特性。结果表明:在相同截面尺寸及喉道面积的条件下,环形喷管出口气流马赫数、气流速度分别比线形喷管高4.03%,0.356%,静温、静压分别比线形喷管低6.08%,19.7%。在喷管的收缩段,两种喷管的边界层发展规律及厚度值基本相同,而环形喷管的气流速度要快于线形喷管,因此环形喷管的氟原子复合比例要略低于线形喷管。     

宽禁带半导体材料技术

宽禁带半导体材料是一种新型材料,具有禁带宽度大、击穿电场高、热导率高等特点,非常适合于制作抗辐射、高频、大功率和高密度集成电子器件;利用其特有的禁带宽度,还可以制作蓝光、绿光、紫外光器件和光探测器件,能够适应更为苛刻的生存和工作环境。在宽禁带半导体材料中,具有代表性的是碳化硅(SiC)、氮化镓(GaN)、氮化铝(AlN)、金刚石以及氧化锌(ZnO),综合叙述了这些材料的特性、发展现状和趋势;并介绍了SiC、GaN、ZnO材料的应用情况和代表性器件的研究进展。     

850nm大功率垂直腔面发射激光器

针对传统顶发射垂直腔面发射激光器(VCSEL)的散热、电极生长以及Au丝引线等难题,研究了一种非闭合型的大功率VCSEL结构,不仅解决了上述问题,还简化了工艺步骤,避免了一些工艺对已形成器件结构造成的损伤,提高了激光器的可靠性以及电流注入效率。利用该结构制作的激光器室温下连续输出最大功率达到46 mW,激射波长为849.5 nm,激射光谱半高宽(FWHM)为0.6 nm;在150 mA的注入电流下,发散角为10°。在室温5、0μs脉冲条件下,测得的最高输出光功率为69 mW。     

QM/MM Study on Enzymatic Mechanism in Sinigrin Biosynthesis

As the major and abundant type of glucosinolates (GL) in plants, sinigrin has potential functions in promoting health and insect defense. The final step in the biosynthesis of sinigrin core structure is highly representative in GL compounds, which corresponds to the process from 3-methylthiopropyl ds-GL to 3-methylthiopropyl GL catalyzed by sulfotransferase (SOT). However, due to the lack of the crystallographic structure of SOT complexed with the 3-methylthiopropyl GL, little is known about this sulfonation process. Fortunately, the crystal structure of SOT 18 from Arabidopsis thaliana (AtSOT18) containing the substance (sinigrin) similar to 3-methylthiopropyl GL has been determined. To understand the enzymatic mechanism, we employed molecular dynamics (MD) simulation and quantum mechanics combined with molecular mechanics (QM/MM) methods to study the conversion from ds-sinigrin to sinigrin catalyzed by AtSOT18. The calculated results demonstrate that the reaction occurs through a concerted dissociative mechanism. Moreover, Lys93, Thr96, Thr97, Tyr130, His155, and two enzyme peptide chains (Pro92-Lys93 and Gln95-Thr96-Thr97) play a role in positioning the substrates and promoting the catalytic reaction by stabilizing the transition state geometry. Particularly, His155 acts as a catalytic base while Lys93 acts as a catalytic acid in the reaction process. The presently proposed concerted dissociative mechanism explains the role of AtSOT18 in sinigrin biosynthesis, and could be instructive for the study of GL biosynthesis catalyzed by other SOTs.     

InAs量子点双区共腔双稳激光器

本文介绍了一种新型的双区结构的InAs量子点激光器,实现了波长1.24μm室温连续激射,同时在对可饱和吸收区施加反向偏压或开路的条件下观察到了明显的光学双稳现象,其回滞宽度优于已知所报道的结果。此外,还发现减小反向偏压或增大吸收区长度能有效增加回滞宽度。应用一个改进的阈值电流模型,揭示了可饱和吸收区内量子点吸收和电吸收两种机制对光学双稳的影响,并对所观察到的实验结果进行了解释。     

视频成像测井光缆传输系统井上电路设计

文章描述了一种基于FPGA实现的井上电路.该电路基于光缆传输机制,采用光模块完成光电转换,在FPGA内实现高速串行数据的数据恢复和曼彻斯特解码等处理,经视频模块处理后,完成对井下视频信息的恢复.其中,高速串行数据的数据恢复采用了过采样的处理方法.该电路结构简单、可靠性较高,与井下电路配合使用,可实现井下视频信号的可靠采集.     

Fabrication of highly reflective gratings in 1.5 μm semiconductor lasers using focused ion beam-based etching

This paper reports on fabrication of semiconductor/air gratings in 1.5 μm double-section semiconductor lasers to achieve a high reflectivity in order to compensate low round-trip gain. Fabrication of the gratings with varying thicknesses and with thicknesses down to 160 nm is carried out at the gain section of the double-section diode laser using focused ion beam etching (FIBE) and inductively coupled plasma (ICP) techniques. Theoretical results of reflectivity are given for 1.5 μm AlGaInAs/InP semiconductor lasers by adding wavelength dependence of the refractive index into the calculations. We also compare our reflectivity results with that of a commercial simulation program and show a good agreement between them. Our results demonstrate that the gratings fabricated consist of only six air/semiconductor layer pairs and achieve theoretical reflectivity higher than 99%. Due to a high index contrast of the both layers, n_l = 1, n_h ∼ 3.5, a reflectivity bandwidth of >230 nm is obtained in 1.5 μm semiconductor lasers. Finally, lasing operation from AlGaInAs/InP semiconductor lasers with highly reflective grating section is achieved with a low threshold current of ∼8 mA, which is almost three times lower than devices without semiconductor/air gratings.     

PML吸收边界条件在波导不连续性问题中的应用

采用矢量有限元方法结合PML吸收边界条件分析波导不连续性问题。利用PML吸收边界条件截断计算区域,可以减少内存消耗;采用模式正交性计算波导结构的S参数,可以获得更加精确的解。在结果验证阶段,分别对PML参数设置、厚度选择、波导介质不连续性以及波导结构不连续性模型进行分析,将计算结果与文献对比,验证了PML吸收边界条件的有限元法分析波导不连续性问题的准确性。     

新型咪唑啉化合物在H_2S/CO_2共存条件下对Q235钢的缓蚀性能

合成了一种新型咪唑啉化合物1-(2-氨基-硫脲乙基)-2-十五烷基-咪唑啉(IM-S),并通过失重法、电化学方法及扫描电镜等研究了IM-S在H2S/CO2共存条件下对Q235钢的缓蚀性能,探讨了其在Q235钢表面的吸附行为.结果显示,IM-S具有较好的抗H2S、CO2腐蚀能力,能同时抑制碳钢腐蚀的阴、阳极反应过程,最高缓蚀效率可达92.74%.缓蚀剂在Q235钢表面呈单分子层吸附,属于以化学吸附为主的混合吸附.最后采用量子化学方法对IM-S的缓蚀机理做了进一步分析.     

铒激光脉冲消融泌尿结石和胆结石比较研究

利用光学弱相干显微成像系统对脉冲激光消融硬生物组织后形成的凹坑二维和三维形貌进行了扫描,分析了Erbium∶YAG激光脉冲消融生物硬组织特性.结果表明:相同激光参量条件下,消融胆结石比消融泌尿结石具有更高的消融效率;消融胆结石或消融泌尿结石时,脉冲能量越大,消融效率越高;消融效率提高主要体现在凹坑表面直径更宽、高度更深...