拼接光栅压缩器的时域特性

在拼接光栅和拼接光栅压缩器的设计中,子光栅调节偏差不可避免,各维偏差与拼接光栅的时间特性之间的关系很关键。通过脉冲压缩理论分析得到各维偏差和聚焦脉冲时间宽度展宽之间的解析关系,从数值计算结果分析,面平行左右偏差对脉冲的时间宽度影响较大,必须控制在21.08 μrad内；条纹密度差异对脉冲宽度的影响很显著,相对条纹密度的比值应控制在10-5以内；从消除角色散的角度分析,面平行俯仰偏差和条纹平行度偏差可以相互补偿,条纹密度差异和面平行左右偏差也可以相互补偿。

Antireflective characteristics of triangular shaped gratings

The antireflection properties of triangular shaped gratings are studied by a combination of the effective medium theory and the anisotropic thin-film theory. The triangular shaped structures are analyzed as a function of grating period, filling factor, and groove depth, and the antireflective characteristics are also studied when visible-infrared light is incident upon them. Numerical examples are given for gratings on glass substrate with refractive index of 1.5. The results show that this kind of grating is capable of reducing reflections, and could achieve very low reflectivity over a wide field of view and a wide waveband by choosing appropriate parameters.

飞秒激光用多层介质膜脉宽压缩光栅的设计

以薄膜光学的干涉理论和衍射光学的傅里叶模式理论为基础，给出了0．8μm飞秒激光器用多层介质膜脉宽压缩光栅的理论设计；设计采用H3L（HL）^9H0．5L2．4H的多层介质膜为基底，当刻蚀后表面浮雕结构的占宽比为0．35，线密度为1480线／mm，槽深为0．2μm，顶层HfO2的剩余厚度为0．15μm时，对于Littrow角度（36．7°）和TE波模式入射的衍射光栅其-1级衍射效率达到95％以上．

鉴别用变方位角导模共振滤光片的设计

设计了在0°和90°方位角下都具有低旁带的鉴别用导模共振滤光片。利用严格的耦合波理论，分析了这种器件在不同入射角、不同光栅槽深和覆盖不同厚度SiO2层情况下的衍射特性。得到了满足鉴别要求的导模共振滤光片结构。在30°入射角情况下，对于TE模式偏振光，设计的滤光片在0°和90°方位角下都有形状对称的反射光谱、低的旁带、两个位置分开的共振峰和适当的半宽度。

梯形介质膜光栅衍射特性分析

基于严格耦合波理论建立了梯形介质膜光栅的衍射机理模型,利用该模型讨论了底角为70°的梯形介质膜光栅-1级的衍射行为。通过对梯形介质膜光栅的占空比、槽深和剩余厚度的优化,设计了应用于1053 nm和51.2°角度入射的梯形介质膜光栅。对于顶层为HfO2的介质膜光栅,当槽深为200 nm,剩余厚度为100 nm,占空比为0.35时,其衍射效率优于99.5%,而对于顶层为SiO2的梯形光栅,为获得99.5%的衍射效率,其槽深为800 nm,剩余厚度为320 nm。而且,获得同样的衍射效率,顶层为HfO2的梯形光栅具有更宽的光谱特性。数值计算表明,严格耦合波理论模型对梯形介质膜光栅衍射效率的计算具有很好的收敛性和稳定性。

Study of the surface plasma transmission properties of a Fabry-Perot resonator by numerical simulation

It is demonstrated with powerful evidence that the extraordinary transmission of a metallic grating is undoubtedly due to the excitation of standing surface plasma waves in the Fabry-Perot like resonator. This is the first time that the strong standing waves set up in the groove of a sub-wavelength double-layer grating (SWDG) for the surface plasma waves have been reported. Moreover, about 90% transmission is gained with an SWDG, more easily fabricated than ordinary metallic gratings, in the first peak of transmission spectrum.

可见光波段双层浮雕型导模共振滤波器设计与分析

基于傅里叶模式理论分析了双层浮雕型导模共振光栅的共振效应,分别讨论了光栅的槽深、剩余厚度、周期以及填充系数对峰值反射率、带宽、旁带反射率的影响.数据计算表明,欠刻蚀情形的误差宽容度远远优于过刻蚀情形,两者在光栅槽深相对误差小于15%的范围内,都能保证共振峰的衍射效率高于99.5%,在相同的误差范围内,共振峰线宽的相对误差将分别达到7%和60%,因此厚度误差集中反映在对共振线宽的改变上.另外,光栅周期和填充系数的变化将明显改变共振峰中心波长和线宽.

Compensation of reflectance response deviations of guided-mode resonant filters induced by overetching fabrication

Unless the fabrication error control is well treated, it easily causes overetched fabrication errors, which causes the resonant peak value deviation during the fabrication process of guided-mode resonant filters (GMRFs). Hence, the fabrication error control becomes a key point for improving the performance of GMRF. We find that, within the range of the groove depth from 93 to 105 nm, the relationship between the overetched error and the resonant peak value deviation is nearly linear, which means that we can compensate the reflectance response deviation and reduce the resonant peak value deviation by the method of covering the layer film on the GMRF. Simulation results show that the deviation is compensated perfectly by this way. (C) 2008 Optical Society of America

Sources of variability in the free-ball micro-scale abrasion test

In the 'free-ball' version of the micro-scale abrasion or ball-cratering test the rotating ball rests against a tilted sample and a grooved drive shaft. Tests under nominally identical conditions with different apparatus commonly show small but significant differences in measured wear rate. An indirect method has been developed and demonstrated for continuous on-line measurement of the coefficient of friction in the free-ball test. Experimental investigation of the effects of sample tilt angle and drive shaft groove width shows that both these factors influence the stability of the rotation of the ball, and the shape of the abrasive slurry pool, which in turn affect the coefficient of friction in the wear scar area and the measured wear rate. It is suggested that in order to improve the reproducibility of this method the geometry of the apparatus should be specified. For the apparatus used in this work with a steel ball of 25 mm diameter, a sample tilt angle of 60-75° and a shaft groove width of about 10mm provided the most stable ball motion and a wear rate which showed least variability. © 2004 Elsevier B.V. All rights reserved.

Enhancing the stability of subsonic compressors using casing grooves

Casing grooves are known to increase the stable operating range of axial compressors. The mechanism by which this stability enhancement occurs is poorly understood. This paper develops a better understanding of the behavior of casing grooves through analysis of new data. An experimental parametric study is used to demonstrate the effect of varying the axial location of a single casing groove on the stability and efficiency of the compressor. The effect that the groove has on rotor outflow blockage, blade loading, and the near-casing flow field is then investigated using both experimental and computational methods. It is found that the interaction of the groove with the flow field is different when the groove is positioned forward or aft relative to the blade. The interaction of the groove with the flow in the tip region in both of these positions is presented in detail. Finally, the implications of these findings for the design of casing grooves of different depths are discussed. © 2011 American Society of Mechanical Engineers.

Stability enhancement by casing grooves: The importance of stall inception mechanism and solidity

This paper concerns the optimisation of casing grooves and the important influence of stall inception mechanism on groove performance. Installing casing grooves is a well known technique for improving the stable operating range of a compressor, but the wide-spread use of grooves is restricted by the loss of efficiency and flow capacity. In this paper, laboratory tests are used to examine the conditions under which casing treatment can be used to greatest effect. The use of a single casing groove was investigated in a recently published companion paper. The current work extends this to multiple-groove treatments and considers their performance in relation to stall inception mechanisms. Here it is shown that the stall margin gain from multiple grooves is less than the sum of the gains if the grooves were used individually. By contrast, the loss of efficiency is additive as the number of grooves increases. It is then shown that casing grooves give the greatest stall margin improvement when used in a compressor which exhibits spike-type stall inception, while modal activity before stall can dramatically reduce the effectiveness of the grooves. This finding highlights the importance of being able to predict the stall inception mechanism which might occur in a given compressor before and after grooves are added. Some published prediction techniques are therefore examined, but found wanting. Lastly, it is shown that casing grooves can, in some cases, be used to remove rotor blades and produce a more efficient, stable and light-weight rotor. © 2010 by ASME.

Enhancing the stability of subsonic compressors using casing grooves

Casing grooves are known to increase the stable operating range of axial compressors. The mechanism by which this stability enhancement occurs is poorly understood. This paper develops a better understanding of the behaviour of grooves through analysis of new data. An experimental parametric study is used to demonstrate the effect of varying the axial location of a single casing groove on the stability and efficiency of the compressor. The effect that the groove has on rotor outflow blockage, blade loading and the near-casing flow field is then studied using both experimental and computational methods. It is found that the interaction of the groove with the flow field is different when the groove is positioned forward or aft relative to the blade. The interaction of the groove with the flow in the tip region in both of these positions is presented in detail. Finally, the implications of these findings for the design of casing grooves of different depths are discussed. Copyright © 2009 Rolls-Royce plc.

Amolops bellulus: A new species of stream-breeding frog from western Yunnan, China (Anura : Ranidae)

We describe a new species of stream-breeding frog of the genus Amolops, Amolops bellulus, from the mountainous region of Lushui County, Yunnan Province, China, near the boundary between Yunnan and Myanmar. This species differs from all its congeners in a combination of morphological characteristics including the absence of a circummarginal groove at the tip of first finger, lack of a supratympanic fold, a white band along the upper jaw extending to shoulder, a black band starting from tip of snout along upper loreal region and extending to anterior flank of body, absence of a vocal sac, tympanum distinct and feebly concave, and the presence of vomerine teeth.

Self-regulating casing treatment for axial compressor stability enhancement

The operating range of an axial compressor is often restricted by a safety imposed stall margin. One possible way of regaining operating range is with the application of casing treatment. Of particular interest here is the type of casing treatment which extracts air from a high pressure location in the compressor and re-injects it through discrete loops into the rotor tip region. Existing re-circulation systems have the disadvantage of reducing compressor efficiency at design conditions because worked flow is unnecessarily re-circulated at these operating conditions. Re-circulation is really only needed near stall. This paper proposes a self-regulating casing treatment in which the re-circulated flow is minimized at compressor design conditions and maximized near stall. The self-regulating capability is achieved by taking advantage of changes which occur in the tip clearance velocity and pressure fields as the compressor is throttled toward stall. In the proof-of-concept work reported here, flow is extracted from the high pressure region over the rotor tips and re-injected just upstream of the same blade row. Parametric studies are reported in which the flow extraction and re-injection ports are optimized for location, shape and orientation. The optimized design is shown to compare favorably with a circumferential groove tested in the same compressor. The relationship between stall inception type and casing treatment effectiveness is also investigated. The self-regulating aspect of the new design works well: stall margin improvements from 2.2 to 6.0% are achieved for just 0.25% total air re-circulated near stall and half that near design conditions. The self-regulating capability is achieved by the selective location and orientation of the extraction hole; a simple model is discussed which predicts the optimum axial location. Copyright © 2011 by ASME.

武汉东湖轮虫种类组成及其分类讨论

作者根据Koste(1978)提出的轮虫分类系统对武汉东湖4个站1991年的轮虫种类进行了分类;同时,对我国以往的轮虫分类中存在的若干问题进行了讨论。 1991年作者共观察到轮虫69种,隶属于19个科,29个属。新记录12种。其中,采自水样的轮虫种类有59种,沉积物中休眠卵萌发的种类41种,两者相同种类31种,休眠卵萌发特有种类10种,其中的盘状鞍甲轮虫(Lepadella patella)、侧刺伏嘉轮虫(Wolga spinifera)、侧扁棘管轮虫(Mytilina cortlpressa)等在60年