Dynamics of radiation scattering by particles of condensed phase in quasicontinuous laser irradiation of metals

Radiation scattering by particles of condensed phase in an ablation plasma plume has been experimentally studied during quasicontinuous laser irradiation (λ = 1.06 μm, q = 0.1–9 MW/cm², τ ∼ 1.5 msec) of duraluminum D16T, aluminum A99, and bismuth. The particle size distribution and the nature of their dispersal during irradiation was studied in scattered light (λ = 0.69 μm) from individual particles that could be visually observed on photographs. It was found that under the pressure developed in the plume, large particles ejected from the irradiated zone can move backward and return to the target (D16T). The plume (Bi) becomes brighter due to ablation of particles in the path of the laser beam. The directional scattering coefficients for scattering from the local zone on the axis of the plume, measured during the laser pulse, were used to study the relationship between the dynamics of entry of condensed phase into the plume, shielding of the target by the particles, and brightening of the plume under the action of the incident laser radiation. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 2, pp. 210–219, March–April, 2006.     

S波段低温低噪声放大器的研制

介绍了基于ADS仿真的低噪声放大器的设计与制作方法;重点研究了LNA的直流偏置、稳定性分析、匹配设计、版图制作和调试;提出了源级负反馈和栅极加并联阻抗的方法来实现了电路全频段稳定和低温正常工作。采用ATF-34143制作了中心频率在2.25的低噪声放大器,在77K温度下,该放大器带内输入输出驻波比小于1.2,增益达到23dB,噪声系数为0.24dB。     

不同重叠排列方式的双层高温超导块材在永磁轨道上方的悬浮特性

研究了永磁轨道上方双层高温超导块材两种不同堆叠方式(籽晶生长线对齐方式和籽晶生长线错开方式)的悬浮特性。实验发现:这两种不同的堆叠方式对悬浮性能有不同的影响。随着场冷高度的增加,它们对悬浮性能的增加效应越来越弱,这种现象对于悬浮力来说尤其明显。场冷高度为10 mm和15 mm时,对悬浮力来说,籽晶生长线对齐堆叠方式与错开方式相比,第一次测量时前者减少的百分比为11.588%和0.870%,第二次测量时为12.693%和1.363%,第三次测量时为12.399%和1.370%。导向力也有类似的结论。经实验可以看出,可以通过优化每一块高温超导块材的具体摆放位置,来提高高温超导磁悬浮车的承载能力和稳定性。同时,这一结果对高温超导磁悬浮轴承、飞轮储能等悬浮间距小的场所也具有一定的参考价值。     

不同环境温度下工艺参数对扩散吸收式制冷机的性能影响

外界环境温度对扩散吸收制冷循环有重要影响,以四台相同结构的扩散吸收式制冷机为基础,用实验的手段研究了不同环境温度下,氨水溶液灌装浓度、充注压力、输入功率等工艺参数对扩散吸收式制冷机性能的影响。得出了实验样机在各工况下的最优工艺参数;研究发现随环境温度的升高,样机的最佳灌装浓度下降,而最佳输入功率和最适宜充注压力升高。可为扩散吸收式制冷机根据环境温度选择各工艺参数提供一定的依据。     

热重分析技术研究聚-α-甲基苯乙烯降解温度

采用热重分析技术研究了4种聚-α-甲基苯乙烯原料和其它微球壳层材料的热降解温度。研究表明,聚-α-甲基苯乙烯原料主要失重温度范围为220～340℃,等离子体辉光放电涂层材料的降解温度为350～450℃。升温速率在20℃/min和30℃/min时,降解温度基本相同,升温速率不影响降解的温度范围,低于20℃/min时,随着升温速率升高,降解温度升高。     

Glassy metallic plastics

This paper reports a class of bulk metallic glass including Ce-, LaCe-, CaLi-, Yb-, and Sr-based metallic glasses, which are regarded as glassy metallic plastics because they combine some unique properties of both plastics and metallic alloys. These glassy metallic plastics have very low glass transition temperature (Tg~25oC to 150oC) and low Young’s modulus (~20 GPa to 35 GPa). Similar to glassy plastics, these metallic plastics show excellent plastic-like deformability on macro-, micro- and even nano-scale in their supercooled liquid range and can be processed, such as elongated, compressed, bent, and imprinted at low temperatures, in hot water for instance. Under ambient conditions, they display such metallic properties as high thermal and electric conductivities and excellent mechanical properties and other unique properties. The metallic plastics have potential applications and are also a model system for studying issues in glass physics.     

高超声速飞行器高温流场对激光武器毁伤效应的影响

以美国ABL系统激光武器为例,分析了高超声速飞行器高温流场气体影响激光武器毁伤效应的一些主要因素,包括气体击穿、等离子体屏蔽效应、烧蚀产物颗粒的影响。结果表明:通常情况下,流场电子数密度小于1017cm-3,流场本身等离子体特性不会引起对激光的等离子体屏蔽效应;只有在0.5 km射程以内和宽脉冲激光引起的高压流场(约10 MPa以上)气体击穿,才会导致明显的等离子体屏蔽效应,但在实际战场条件下这种情况一般不会发生;对采用烧蚀手段进行防热的飞行器而言,飞行高度大于10 km,并且基于自由来流流量的无量纲化烧蚀流量小于10-2左右时,烧蚀产物颗粒不会引起激光的衰减。     

无加热氧碘化学激光器超音速喷管

针对氧碘化学激光器的金属喷管在使用过程中需加热保温且存在结构复杂、故障率高等问题,初步选择了几种可用于加工无加热喷管的非金属材料,并以kW级氧碘化学激光器为原型,以聚酰亚胺为例,对激光器运行条件下的喷管温度场进行数值模拟,以验证此种非金属无加热喷管的可行性。结果表明:与金属喷管相比,非金属喷管在不加热保温的情况下能够有效阻止热量传递,防止碘蒸气冷却凝结,满足激光器喷管的使用要求。     

介质厚度对光量子阱束缚态波长的调整

用传输矩阵法计算了不同介质厚度对光量子阱结构的传输特性。计算结果表明:光子的束缚效应将导致波长的量子化。通过微小地改变阱区和垒区介质的厚度可改变束缚态的波长,且阱区和垒区介质厚度的变化与束缚态波长的变化呈良好的线性关系,阱区介质厚度的变化对束缚态波长的变化大于垒区。阱区介质厚度与束缚态半峰宽呈阶梯形状降低,而阱区介质厚度与束缚态品质因子呈阶梯形状升高。此结果为设计所需要的束缚态波长光量子阱结构提供了理论依据,也为光量子阱实现热敏开关提供了理论基础。     

相位延迟器在四频激光陀螺中的应用研究

介绍了典型相位延迟器1／4波片和90°相位延迟膜的工作原理,定义了四频激光陀螺输出信号解调信噪比,分析了相位延迟量对其造成的影响,并就此结果进行了MATLAB仿真。从两种相位延迟器的工作原理出发,阐述了温度、入射角、入射光波长等因素对两者相位延迟量的影响。结合激光陀螺在实际应用中的要求,对两者进行了比较,并得出结论：90°相位延迟膜更适合作为四频激光陀螺输出解调系统中的相位延迟器。