共查询到16条相似文献，搜索用时 203 毫秒
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研究了部分相干贝塞尔光束经过光阑透镜聚焦后的光强分布。研究表明．部分相干贝塞尔光束在几何焦点附近的光强分布不仅取决于阶数和贝塞尔光束系数,还与相干度有关。据此,可以通过选择合适的参数。产生部分相干局域空心光束。产生的局域空心光束运用广泛,如微粒导引,捕获和诱导旋转等等。还有一些研究者采用局域空心光束来构成激光导管、光学镊子和光学扳手,从而实现微观粒子的精确、无接触操纵和控制。 相似文献
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研究了部分相干高斯-谢尔模型光束经过整数阶螺旋形位相板之后形成的部分相干涡旋光束,着重研究这种部分相干涡旋光束的传输特性。研究结果表明,这种光束在传输中呈现出环状结构的特点;整数阶螺旋形位相板的阶数越高,环状结构的半径越大：当入射的部分相干高斯-谢尔模型光束的空间相干度降低到一定程度时,环状结构消失了。此外,还研究了入射光束的空间相干度对衍射场中的光谱相干度的影响。 相似文献
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基于矢量德拜理论,研究了双环角向偏振涡旋光束经大数值孔径透镜的聚焦,且在聚焦场中考虑存在两种不同介质。研究表明当涡旋光束的拓扑电荷数为1,且当透镜孔径半径与入射双环角向偏振涡旋光束的束腰半径之比为1.5时,聚焦光束可得到一个尺寸只有零点几个波长的局域空心光束。局域空心光斑的横向半径仅为0.38λ,而空心长度为2.37λ。此外还研究了透镜的数值孔径以及光束的入射拦截比对不同介质引起聚焦光束焦移的影响。 相似文献
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从部分相干光的传输理论出发,推导出了高斯-谢尔模型光束所描述的部分相干光通过夫琅禾费单缝衍射后光强分布的表达式,通过数值计算对这种光束通过单缝光阑系统后观察屏上的光强分布特点进行了讨论,并和完全相干高斯光束的情况做了对比分析。结果表明,通过单缝系统后部分相干光在观察屏上的光强分布与光场空间相干性、单缝系统的缝参量和观察屏到入射屏的距离有关,并且对这几种因素的影响进行了分析。 相似文献
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本文从部分相干光的传榆理论出发,推导出高斯-谢尔模型(GSM)光束所描述的部分相干光通过光阑像散透镜后轴上的表示式,并通过数值计算对部分相干光通过光阑像散透镜后的传榆特性进行了分析.研究结果表明,被光阑像散透镜聚焦的部分相干光在其轴上的光强特性与光阑衍射、光场的相干性和透镜的像散有关.并对比分析了有像散和无像散两种情况下部分相干光的传输特性. 相似文献
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利用部分相干光的张量ABCD定律，采用解析的方法研究了部分相干的非轴对称高斯-谢尔模（GSM）光束在高斯型光腔内的频谱演化特性，结果表明非轴对称GSM光束的相对频移与振荡的次数以度光腔的参数有关．解析的分析方法避免了已往处理部分相干光频谱演化时采用数值积分所带来的计算冗长的问题，并且适用于任意的傍轴光学系统． 相似文献
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采用部分相干光的传输理论,推导出了部分偏振高斯-谢尔模型光束传输的3×3阶交叉谱密度矩阵的解析表达式。与其傍轴传输相比,纵向场成分的出现不仅改变了光强在横截面上的对称性分布,还对部分偏振高斯-谢尔模型光束的相干性质和偏振性质产生重要影响。 相似文献
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利用变分法研究了1＋1维傍轴高斯光束型在含有小损耗的弱非局域非线性介质中的传输特性,得到了光束各参量的演化方程和一个临界功率。在介质损耗足够小的前提下,当光束初始功率等于临界功率时,得到了一个束宽随传输距离缓慢展宽的准空间光孤子——损耗空间光孤子。 相似文献
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依据非局域非线性薛定谔方程和强非局域非线性自散焦介质的特性,通过对强非局域非线性自散焦介质的响应函数作两次泰勒展开,使非局域非线性薛定谔方程近似简化为一个线性方程,并由此来研究1+2维傍轴高斯光束在强非局域非线性自散焦介质中的传输特性,得到了光束各参量的演化方程和束宽的演化规律.其结果表明:在强非局域非线性自散焦介质中,傍轴高斯光束的束宽随传输距离将不断展宽,不能形成空间孤子. 相似文献
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Lately, scholars have argued that there is a consensus on a number of critical features of effective teacher professional development (PD). This study presents the results of a systematic review of one of these features: coherence. The analysis and synthesis of 95 papers show that coherence in PD is conceptualized in various ways, and thus that the aforementioned consensus can be questioned. For example, should PD (1) be coherent with external factors, such as standards and assessments; (2) be internally coherent, for example that activities within PD programs should be aligned; or (3) create coherence between goals that are either predetermined or negotiated together with teachers? The different conceptualizations of coherence all implicate how teachers are positioned in relation to PD programs and, in the light of our results, we argue that teachers are primarily seen as implementers expected to align their instruction with external and predetermined goals and practices. 相似文献
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仇云利 《广东技术师范学院学报》2008,(9)
研究了部分相干厄米高斯光束在自由空间的傍轴传输性质,根据交叉光谱密度函数得到了不同模阶数的光强分布、平均光束束宽和光束质量因子的解析表达武,结果表明相干长度对光强分布影响较大,较高的模阶数使得光束展宽得越快,光束质量变差,且这两个光束参量的关系与部分相干厄米高斯光的相干长度无关. 相似文献
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基于广义惠更斯-菲涅耳原理,利用Yura期展宽理论和ITu-R大气结构模型,研究斜程湍流大气部分相干高斯-谢尔（GSM）光束的短期光束展宽。根据推导的解析表达式,得出短期光束展宽小于长期光束展宽。数值模拟了短期光束展宽随波长、初始半径、接收机高度、光源相干性的变化。结果表明：当增加入射波波长、增大波束初始半径、提高接收机高度时,光源相干性变差,短期光束展宽变小,受大气湍流影响小,有利于激光通信。 相似文献
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Glenn Fulcher 《Journal of Research in Reading》1989,12(2):146-163
What is the relationship between cohesion and coherence? Researchers in the field of Applied Linguistics have traditionally attempted to list and define the cohesive devices in English which provide the basis for coherent text. Schema theoreticians, on the other hand, have argued that coherence is primary, that readers look for coherence given their existing schemata and extra-linguistic knowledge of the world and only then do they recognise cohesion. This paper looks at these two approaches in the light of the conflict which has grown up around the relationship between the concepts of cohesion and coherence and suggests that the positions taken are the result of a theoretically different starting point. If the researcher is primarily interested in linguistic analysis then she will begin with cohesion whereas, if human psychology in the reading process is the main focus then it will be more natural to look at coherence. However, it seems to be at least intuitively obvious that both the text itself and the reader have a part to play in the reading process, that reading is simultaneously data-driven and concept-driven. It is suggested that these two approaches would benefit from being a part of a larger theory of the reading process. In this context the work of Ruqaiya Hasan is reviewed as the most thorough attempt to provide a theory of text which accounts for both cohesion and coherence. Secondly, data are presented which suggest that a theory which integrates cohesion and coherence is necessary. Two studies are reported: an informal classroom experiment on the influence of pronominal reference on comprehension and an analysis of the results of a test designed to examine the relationships between theoretical constructs hypothesised to constitute (at least part of) the superordinate term “reading comprehension”. 相似文献