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光学综合孔径成像技术实验研究 总被引:2,自引:0,他引:2
根据光学综合孔径成像系统的成像质量与点扩散函数和光学传递函数的关系,以G o lay-3阵列结构为例,从空间域和频率域对光学综合孔径成像技术进行理论仿真和实验研究。在空间域从理论上分析光学综合孔径成像系统的点扩散函数,对复杂目标的成像通过目标函数与点扩散函数的卷积求得,点扩散函数决定了成像质量。通过数值仿真和模拟实验取得了点扩散函数强度分布图,两者分布规律一致证明理论分析正确。在频率域研究光学综合孔径调制传递函数,理论仿真和实验取得的调制传递函数表明,空间域和频率域内光学综合孔径成像技术的理论分析与实验结果具有较好的一致性。 相似文献
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依据基尔霍夫衍射理论,利用幂级数展开的方法,推导出傍轴条件下高斯光束的矩孔及单缝衍射的近似计算公式,并通过数值计算、数值模拟等方法对衍射场的基本特性进行了讨论。 相似文献
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The modified synthetic transmit aperture (STA) algorithm is described. The primary goal of this work was to assess the possibility to improve the image quality achievable using synthetic aperture (SA) approach and to evaluate the performance and the clinical applicability of the modified algorithm using phantoms. The modified algorithm is based on the coherent summation of back-scattered RF echo signals with weights calculated for each point in the image and for all possible combinations of the transmit-receive pairs. The weights are calculated using the angular directivity functions of the transmit-receive elements, which are approximated by a far-field radiation pattern of a narrow strip transducer element vibrating with uniform pressure amplitude over its width. In this way, the algorithm takes into account the finite aperture of each individual element in the imaging transducer array. The performance of the approach developed was tested using FIELD II simulated synthetic aperture data of the point reflectors, which allowed the visualization (penetration) depth and lateral resolution to be estimated. Also, both simulated and measured data of cyst phantom were used for qualitative assessment of the imaging contrast improvement. The experimental data were obtained using 128 elements, 4 MHz, linear transducer array of the Ultrasonix research platform. The comparison of the results obtained using the modified and conventional (unweighted) STA algorithms revealed that the modified STA exhibited an increase in the penetration depth accompanied by a minor, yet discernible upon the closer examination, degradation in lateral resolution, mainly in the proximity of the transducer aperture. Overall, however, a considerable (12 dB) improvement in the image quality, particularly in the immediate vicinity of the transducer’s surface was demonstrated. The modified STA method holds promise to be of clinical importance, especially in the applications where the quality of the “near-field” image, that is the image in the immediate vicinity of the scanhead is of critical importance such as for instance in skin- and breast-examinations. 相似文献
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The rich available transverse intensity structure of vector Bessel-Gauss beams make it important to probe into the focusing property by high numerical aperture objective. In this paper, we obtain the analytical expressions of azimuthally, radially and longitudinally polarized components in the focal area of the objective after tight focusing. Theoretical analysis and the numerical simulation show that, the transverse intensity distributions of the focused beams still have doughnut-like structure, two separate peak structure and circularly aligned array structure. The focused beam spots obtained by an objective with annular aperture usually have smaller spots than with circular aperture. The focused beam of the vector Bessel-Gauss beam with lowest mode number m = 0 is a radially and azimuthally polarized doughnut-like beam with no longitudinal component. These properties and results are useful in optical trapping and particle alignment. 相似文献
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根据波像差理论,推导了光学合成孔径成像系统单个子孔径存在各种像差时波面方差与子孔径数(N)的关系。推导结果表明,piston误差对系统的影响最大,其次是离焦误差、倾斜误差、球差、彗差和像散。运用离焦误差对piston误差、球差和像散进行像差平衡,其效果显著,特别是球差引起的波面方差下降90%。系统各项像差系数随子孔径数的增加而降低;当子孔径数大于6时,各像差系数变化缓慢。根据瑞利判据,计算N(N≤6)个子孔径合成系统的像差允限和相应的3孔径系统的斯特列尔比。 相似文献
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本文对散斑剪切照像术中傅里叶滤波平面的光场分布进行了讨论,得出滤波系统频谱面上的光场分布是以孔径函数的自相关和互相关的边界为周界;对最佳拍摄孔径的设计作了探讨,认为采用适当分离的孔径可以研善波效果,提高条纹的质量。实验的验证结果与理论相吻合。 相似文献
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Focusing of elliptically polarized Gaussian beams through an annular high numerical aperture 下载免费PDF全文
Based on the vectorial Debye theory,the focusing properties of the Gaussian beam through an annular high numerical aperture are studied numerically,including the intensity,the phase and the orbital angular momentum properties.Then the influence of certain parameters on the focusing properties is also investigated.It is shown that sub-wavelength elliptical light spots can be obtained.And there exists a vortex in the longitudinal component of the focused field even though the incident beam is Gaussian beam,indicating that the spin angular momentum of the elliptically polarized Gaussian beam is converted into the orbital angular momentum by the focusing. 相似文献
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针对ICF系统要求,提出了一种基于统计理论的大口径光学元件功率谱密度测量方法。该方法将大口径波前划分成足够多个子区域,分别求得每个子区域波前的功率谱密度,根据统计理论可将大口径波前功率谱密度表示为各个子区域波前功率谱密度的加权平均,其权重因子是各子区域对应的面积。模拟计算和实验结果验证了统计法测量的有效性,并表明当子区域个数大于等于8×8时,统计法测量和子孔径拼接测量得到的功率谱密度吻合较好。统计法测量对平台移动精度和环境稳定性要求不高,可应用于大口径光学元件功率谱密度的过程检测。 相似文献
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In this paper, we present a generalization of the so-called Frozen Waves, which are new solutions to Maxwell’s equations having the important characteristic of remaining static in space and keeping any previously chosen arbitrary longitudinal field pattern. In the pioneering work, these waves were introduced as a discrete superposition of zero-order Bessel beams. As a fact, here we will represent these waves as a continuous superposition of Bessel beams leading to a simpler and more compact mathematical formalism, which allows us to derive certain inequalities that restrict the physical properties of the Frozen Waves, such as their attainable longitudinal resolution. Besides this, we will discuss losses compensation in a lossy medium and, finally, their practical realization through finite apertures. 相似文献
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大数值孔径光学系统表面光线的入射角较大, 会导致薄膜的偏振分离, 诱发偏振像差, 影响光学系统的聚焦特性. 本文利用矢量光衍射理论, 建立了光学薄膜各参量与光学系统聚焦光场的模型. 利用该模型分析了线偏振光入射时, 光学薄膜对光学系统聚焦光斑的扰动. 在此基础上, 探讨了应用了不同约束条件下得到的光学薄膜对最终聚焦光场的影响, 确定了减小薄膜扰动光学系统光斑的设计方法, 即额外添加透射率差和位相差的约束条件, 并且适当增加位相差约束的权重. 利用该方法优化设计的薄膜, 相比于普通减反膜而言, 对系统聚焦光场中心强度的提升可达约12.5%. 相似文献
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研究了半径随角度的变化而随机变化的圆孔波纹锯齿光阑的衍射特性,提出并证明半径随机的圆孔纹波锯齿光阑能改善光束的近场分布和抑制光束中央部分的衍射调制。给出了衍射光轴上和横截面内光强分布的模拟计算结果,通过计算结果可以看出:通过半径随机圆孔波纹锯齿光阑后,衍射光横截面内填充因子比经过调幅型波纹锯齿光阑后的填充因子高,调制强度比经过调幅型波纹锯齿光阑低,并且半径随机锯齿光阑能在较大的空间范围内抑制轴上光强的衍射调制, 其可抑制的最远空间距离可达0.15 m。 相似文献
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针对机载平台激光3D成像系统的轻小型需求,设计了采用APD阵列的共口径激光收发光学系统。在分析激光成像系统照明方式及其光学系统结构的基础上,给出了激光3D成像光学系统结构框图:激光经衍射元件实现分束照明,采用双工反射镜实现收发光路的耦合。该光学系统用于2 km以内的目标三维成像,根据激光测距方程,确定了接收光学系统的参数以获得满足信噪比的回波能量。为避免造成像素之间串扰,设计了5倍扩束比的发射光学系统。最后,采用偏振片与1/4波片相结合的方式消除杂光,降低了发射光路对接收光路的影响。设计结果表明:接收光学系统弥散斑直径小于120μm,畸变小于0.2%。该光学系统体积小、重量轻,成像质量良好,可为同类激光成像光学系统提供借鉴参考。 相似文献