共查询到20条相似文献,搜索用时 46 毫秒
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The performance of pupil filters consisting of two zones each of constant complex amplitude transmittance is investigated. For filters where the transmittance is real, different classes of potentially useful filter are identified and optimized. These include leaky filters with an inner zone of low amplitude transmittance, pure phase filters with phase change of π, and equal area filters. The first of these minimizes the relative power in the outer rings for a given axial resolution, the second maximizes the Strehl ratio for a given transverse resolution, and the third minimizes the relative power in the outer rings for a given transverse resolution. Complex filters can give an axially shifted maximum in intensity: the performance parameters calculated relative to the true focus are investigated for some different classes of filter, but filters with phase change not equal to π are found to give inferior performance to the real value filters. 相似文献
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S.-L. Guo M. Ganz M. Fuest P. Vater R. Brandt 《Isotopes in environmental and health studies》2013,49(6):272-273
The flow rate of some liquids (water, heptane, toluene, xylene, dodecane) through Kapton nuclear track filters has been measured. The results can be interpreted with a modified Poiseuille formula. The influence of the viscosity of the liquids on their throughput through Kapton nuclear track filters has been determined. The purification of liquids with Kapton filters has been investigated. It is possible to measure the density of solid particles in deionized water by using Kapton filters. Consequently, nuclear track filters can remove solid particles from high-purity liquids. The soaking effect of some common liquid chemicals on Kapton filters has also been studied, no such soaking could be observed in most of the cases. Finally, these Kapton nuclear track filters are compared with a filter device from Hamamatsu (Japan). 相似文献
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《中国物理 B》2015,(5)
The angular resolutions of the phase-shifted Rugate thin-film filters, the ultra-narrow bandpass filters, and a cutoff filter-combination device are discussed, and the electric field distributions of the filters are compared. The results show that the three transmitting multi-layer thin-film filters can realize the same angular resolution, but the electric field in the cutoff filter-combination device is the lowest. Because a lower electric-field distribution corresponds to a higher laser-induced damage threshold of the thin films, the cutoff filter-combination device may replace the traditional spatial filters in high power laser systems. 相似文献
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Split spectrum processing is a frequency diversity technique used to enhance the signal-to-noise ratio of ultrasonic signals. Traditionally, many Gaussian bandpass filters are used to achieve frequency diversity. This paper introduces an alternative method of obtaining frequency diversity wherein raised-cosine bandpass filters with flat-tops are recommended for use. The reasoning behind the use of raised-cosine filters is outlined. Experimental results are provided to demonstrate the advantages of the raised-cosine filters over Gaussian filters. Finally, the limitation of the new filters is experimentally shown. 相似文献
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The effect of the third-order filter term on soliton interactions in optical fibers with guiding filters is theoretically analyzed. We find that this term causes a significant difference to the interaction of solitons through filters among the regimes of without sliding, with up- and down-sliding frequencies of filters. It is shown that the interaction between solitons can be more effectively suppressed by up-sliding filters than that by down-sliding filters in the presence of the third-order filter term. Moreover, the third-order filter term is found to play a positive role in suppressing soliton interactions in the case of non-sliding. 相似文献
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Stack filters are more general and robust nonlinear filters than median filter, which possess threshold decomposition and stacking properties. Stack filters can be carried out one step using optical parallel fuzzy logic technique instead of three steps in threshold decomposition. All window, width 3 stack filters but two trivial stack filters are expressed in unified expression with coefficiencies to choose desired stack filter, so they are realized by an optical approach, window 3×3 separable stack filters can be realized by cascading the window width 3 stack filters. Window width 5 stack filters can be realized using the same method. 相似文献
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W. S. Hu Q. J. Zeng Y. H. Jing 《Chinese Journal of Lasers》1998,7(6):542-546
1IntroductionWavelengthdivisionmultiplexing(WDM)isacostefectivewaytomakefuluseofthebroadbandwidthoftheopticalfiberwhenthetr... 相似文献
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Abner Shimony 《Foundations of Physics》1971,1(4):325-328
With the use of a suitable assumption about the structure of the class of experimental filters, it is shown that the sequence of alternating replicas of two filters is their greatest lower bound, as Jauch suggests. A generalization of his suggestion yields the greatest lower bound of a denumerable set of filters. The criteria of admissibility of filters are briefly discussed. 相似文献
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微缺陷对薄膜滤光片环境稳定性的影响 总被引:4,自引:2,他引:2
用热蒸发方法沉积了薄膜滤光片.并将样品分别在去离子水中浸泡10天和30天.通过分光光度计、光学暗场显微镜、及扫描电子显微镜等多种测试手段,对诱导透射滤光片在潮湿环境下的稳定性进行了研究.实验发现,在潮湿环境下滤光片产生的膜层分离都是从薄膜中微缺陷点处开始发生和发展的,微缺陷是影响滤光片环境稳定性的重要原因之一,其中杂质和针孔是滤光片中两种最常见的微缺陷.EDS能谱分析进一步表明,薄膜中杂质缺陷成分即为Al2O3膜料本身,所以不能推测,薄膜沉积中的喷溅可能是微缺陷产生的根本原因,抑制喷溅可以有效提高薄膜滤光片的环境稳定性.最后还用扩散理论对微缺陷引起滤光片失效的机理进行了分析. 相似文献
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Statistical evaluation of clutter filters in color flow imaging 总被引:3,自引:0,他引:3
The filter used to separate blood signals from the tissue clutter signal is an important part of a color flow system. In this paper, statistical detection theory is used to evaluate the quality of the most commonly used clutter filters. The probability of falsely classifying a sample volume as containing blood is kept below a specified threshold. With this constraint, the probability of correctly detecting blood is calculated for all the filters. Using a measured clutter signal, we found that polynomial regression filters and projection-initialized IIR filters are best among the commonly used filters. The probability of correctly detecting blood with velocity 10.1 cm/s was 0.32 for both these filters. The corresponding value for the optimal detector was 0.81, whereas a regression filter that depends on the clutter signal statistics achieved a blood detection probability of 0.72. 相似文献
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普通彩色相机加载宽带滤光片构造的多通道光谱采集系统的光谱重建性能与滤光片的选用密切相关。针对上述问题,提出基于主成分分析法的合成滤光片设计方法,旨在获得具有较高光谱重建性能并对所有图像场景均适用的最优滤光片组合。在收集多个宽带滤光片的基础上,测得其透射率并转换成矩阵形式;采用主成分分析方法提取该矩阵的前2个主成分,标准化处理后的主成分即为所求合成滤光片的透射率。为了验证上述方法获得的滤光片的性能,利用色差和光谱均方根误差2个指标对加载了合成滤光片的仿真采集系统的光谱重建精度进行了评价。实验结果表明:采用该方法得到的滤光片组合优于常用方法得到的滤光片组合, 用其构造的成像系统具有较高的色度重建精度和光谱重建精度,此外,改变目标场景颜色特性,其重建性能保持稳定。 相似文献
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Super-resolution filters based on a Gaussian beam are proposed to reduce the focusing spot in optical data storage systems. Both of amplitude filters and pure-phase filters are designed respectively to gain the desired intensity distributions. Their performances are analysed and compared with those based on plane wave in detail. The energy utilizations are presented. The simulation results show that our designed super-resolution filters are favourable for use in optical data storage systems in terms of performance and energy utilization. 相似文献
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Parameters of van der Lugt holographic matched filters for phase and amplitude transparencies, including random phase masks, are studied. Conditions for recording such filters in a phase self-developing photopolymer are determined. A significant difference in the recording conditions for the holographic filters for amplitude transparencies and phase masks is demonstrated. The holographic filters for phase masks with a signal-to-noise ratio of 20–40 dB and η from 6 to 70% that are recorded in the photopolymerizable composition seem to be promising for optical pattern recognition. 相似文献