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A very simple sufficiency condition is obtained, under which the Debye diffraction integral may be expected to give a good approximation to the solution of a boundary value problem that is generally taken to represent a field in the region of focus. When the angular aperture of the focusing system is sufficiently small, the condition reduces to the requirement that the Fresnel number of the diffracting aperture, when viewed from the geometrical focus, is large compared to unity. 相似文献
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Focusing of an atomic beam by a Fresnel atom microlens formed by an optical field diffracted by an aperture whose size is comparable to or greater than the radiation wavelength is considered. It is shown that the dipole gradient force enables one to focus the atomic beam to a spot of about 10 nm in diameter. The focusing properties of a Fresnel atom microlens are analyzed within a model describing the dipole interaction of rubidium atoms with monochromatic radiation near the D-line. 相似文献
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The problem of diffraction of a spherical wave with Gaussian amplitude distribution on two infinitesimally thin and ideally reflecting screens with apertures on an optical axis is solved within the quasi-optical approximation. It is shown that when a Gaussian beam illuminates a bicomponent diffraction system with small Fresnel numbers in a near zone of the second screen, the effect of diffractive multifocal focusing of radiation is observed. In this case, the diffraction picture from the second screen in the focal planes represents the circular nonlocal bands of the Fresnel zones with a bright narrow peak at the center, whose intensity can exceed by six times the value of the incident wave intensity. The energy efficiency of diffractive focusing of Gaussian beams by the bicomponent diffraction system can be as high as 70%. The proposed diffractive method allows the focusing of the wide-aperture beams without using classical refraction elements such as lenses and prisms, and it is applicable to both low-intensive and high-power radiation. 相似文献
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The problem of diffraction of a spherical wave with Gaussian amplitude distribution on two infinitesimally thin and ideally reflecting screens with apertures on an optical axis is solved within the quasi-optical approximation. It is shown that when a Gaussian beam illuminates a bicomponent diffraction system with small Fresnel numbers in a near zone of the second screen, the effect of diffractive multifocal focusing of radiation is observed. In this case, the diffraction picture from the second screen in the focal planes represents the circular nonlocal bands of the Fresnel zones with a bright narrow peak at the center, whose intensity can exceed by six times the value of the incident wave intensity. The energy efficiency of diffractive focusing of Gaussian beams by the bicomponent diffraction system can be as high as 70%. The proposed diffractive method allows the focusing of the wide-aperture beams without using classical refraction elements such as lenses and prisms, and it is applicable to both low-intensive and high-power radiation. 相似文献
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The applicability of different types of Fresnel acoustic lenses as antenna array systems in acoustic brightness thermometry of biological tissues is theoretically and numerically analyzed. On the basis of the technical feasibility criterion formulated for these systems, the wavelength suitable for the use in acoustic thermographs with arrays in the form of Fresnel lenses is determined. The focusing properties of different Fresnel lenses are analyzed. A method for constructing Fresnel lenses that is based on varying the focusing distances is proposed. The method provides an opportunity to design trifocal antenna systems with improved focusing properties. 相似文献
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从理论上研究部分相干光被一环形透镜聚焦,在焦点附近的轴上点的光强分布。研究结果表明,当部分相干光被一环形透镜聚焦时,最大聚焦光强不在几何焦点,而是位于透镜与几何焦点之间,出现焦移现象。并且,焦移量不仅依赖于透镜外半径的菲涅耳数,还依赖于部分相干光的空间相干度和中心拦截比。透镜的菲涅耳数越小,焦移越大;部分相干光的空间相干度越低,焦移越大。当菲涅耳数一定时,环形透镜的中心拦截比越大,焦移越大;当空间相干度很小时,情况就变得比较复杂。 相似文献
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基于Richards-Wolf矢量衍射积分公式, 研究了径向偏振涡旋光束在振幅和相位调制下的4pi聚焦特性.振幅调制是通过振幅滤波实现, 即改变入射光束起始积分值达到调节,相位调制是通过添加相位延迟角δ 的液晶相位延迟器来改变入射光束的偏振态.模拟结果显示,随着振幅的减小, 4pi聚焦系统焦点附近的光轴上呈现出多光球结构; 而相位调制对焦点附近的光强分布产生拉伸作用, 即调节入射光束的拓扑核m和相位延迟器的延迟角δ,可以得到特殊的光强分布. 随着相位δ增大, m=0产生的多光球结构慢慢向光链结构转变,最终变成暗通道;而m=1产生的光链结构慢慢变成光球结构; m=2产生的暗通道变成光球和光链叠加的结构, 这种特殊聚焦光束在光学微操纵领域具有潜在的应用价值.
关键词:
物理光学
偏振
光链
4pi聚焦系统 相似文献
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近距离数字全息术记录和再现问题 总被引:2,自引:0,他引:2
讨论了记录距离小于菲涅耳衍射要求的近距离数字全息记录和再现问题。对全息记录与再现中高次相位的补偿问题进行了分析,证明了在CCD的参量和记录距离给定后,只要记录时使物体的大小、球面参考光波的位置和距离满足一定的条件,即使在记录距离小于菲涅耳衍射要求的最小距离情况下,也可将高次相位的影响补偿到足够小,使得近距离数字全息的数字再现仍可用快速傅里叶变换算法计算。推导出了满足高次相位补偿的条件和满足补偿条件时的数值再现计算公式。实验结果与理论分析的结论相吻合,并给出了一种修正实际记录的参考光和计算机模拟的理想参考光之间偏差的方法。 相似文献
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Flicker RC 《Optics letters》2001,26(22):1743-1745
The way in which the sequence of phase correction impinges on performance in multiconjugate adaptive optics systems is described. When multiple phase modulators with different conjugate ranges are used, the conjugate images of the phase modulators in the atmosphere must be reimaged in the reverse order post focus, and adaptive phase correction applied in this sequence for perfect amplitude and phase cancellation. Performing the correction without relay optics results in residual amplitude and phase aberrations. It is shown, by Monte Carlo simulations of Fresnel propagation, that the effects of wave optical propagation become nonnegligible at visible wavelengths and for large air masses. 相似文献
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实验提取了弱散射体产生的菲涅耳极深区的散斑场.发现当散射距离一定时,弱散射体光场的相位分布特征随散射体的粗糙度的变化而变化;对于某一弱散射体,相位分布特征随散射距离的变化而变化;当弱散射体的粗糙度大到一定程度时,才产生相位涡旋现象;散射体表面上存在相位涡旋;弱散射体产生的相位涡旋的密度随散射屏粗糙度的增大而增大,还随散射距离的增大而增大.研究结果对于认识弱散射体的相位及相位涡旋分布特征随粗糙度和散射距离的演化具有重要意义,而且对于认识散斑场随散射距离的演化有一定的帮助. 相似文献
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QIAO DongHai LI ShunZhou & WANG ChengHao Institute of Acoustics Chinese Academy of Sciences Beijing China 《中国科学G辑(英文版)》2007,50(1):41-52
The acoustic field distributions and the convergent beams generated by the planar-structure Fresnel zone transducers on solid surface are investigated. Because only 0 and 180 degree phase transducers are used, an imaging system with the Fresnel zoom lens could work at very high frequency, which overcomes the frequency limit of the traditional phased array acoustic imaging system. Simulation results are given to illustrate the acoustic field distributions along the focal axis and the whole plane as well. Based on the principle of scanning of the focus with the change of frequency for the excited signal, an experimental imaging system is also built. Acoustic Fresnel zone transducers are fabricated at center frequency of 400 MHz. Measurements and detections of the known hole flaws at different depths of the fused quartz sample are presented to show that the imaging system with Fresnel zoom lens could move its focus by only changing the frequency of the excited signal. 相似文献
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部分相干修正贝塞尔高斯光束通过球差透镜的聚焦特性 总被引:2,自引:2,他引:0
由部分相干光的传输理论出发,对部分相干修正贝塞尔高斯光束通过球差透镜聚焦后轴上光强分布进行了研究.数值计算表明:当光谱相干度较小时,正、负球差对应的最佳聚焦点位于无球差时对应的最佳聚焦点的两侧;当光谱相干度较大时,正、负球差对应的最佳聚焦点将位于无球差时对应的最佳聚焦点的左侧.研究进一步表明,最佳聚焦点随着透镜菲涅耳数的增大向几何焦点方向靠近,并趋于一个定值.当光束菲涅耳数为1时,无球差时对应的最佳聚焦点逐渐趋于0.908,该值与光谱相干度无关,当透镜具有球差时,该值与光谱相干度有关. 相似文献
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The problem of diffraction of a spherical wave with Gaussian amplitude distribution on two infinitesimally thin and ideally reflecting screens with apertures on an optical axis is solved within the framework of the quasi-optical approximation. It is shown theoretically and experimentally that when a Gaussian beam illuminates such a type of bicomponent diffraction system with small Fresnel numbers in a near zone of the second screen, the effect of diffractive multifocal focusing of radiation is observed. In this case, the diffraction picture from the second screen in the focal planes represents the circular nonlocal bands of the Fresnel zones with a bright narrow peak at the center, whose intensity can exceed by six times the value of the incident wave intensity. The energy efficiency of diffractive focusing of Gaussian beams by the bicomponent diffraction system can be as high as 70%. The diffractive method proposed allows the focusing of wide-aperture beams without using classical refraction elements such as lenses and prisms, and it is applicable to both low-intensity and high-power radiation. 相似文献
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A polarization-independent and high-diffraction-efficiency Fresnel lens is developed based on blue phase liquid crystals (BPLCs). The optically isotropic characteristic of BPLCs is used to produce a polarization-independent Fresnel lens. The small optical phase shift of BPLCs that is induced by the Kerr effect is sufficient for the BPLC Fresnel lens to have high theoretical and experimental diffraction efficiencies of 41% and ~34%, respectively. An electrically erasable memory effect in the focusing diffraction at an electric field E>4.44?V/μm is observed. The electro-optical properties of the BPLC Fresnel lens are analyzed and discussed. 相似文献
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Di Yuan Jun-Long Tian Fang Lin Dong-Wei Ma Jing Zhang Hai-Tao Cui Yi Xiao 《Frontiers of Physics》2018,13(3):130504
In this study we investigate the collective behavior of the generalized Kuramoto model with an external pinning force in which oscillators with positive and negative coupling strengths are conformists and contrarians, respectively. We focus on a situation in which the natural frequencies of the oscillators follow a uniform probability density. By numerically simulating the model, it is shown that the model supports multistable synchronized states such as a traveling wave state, π state and periodic synchronous state: an oscillating π state. The oscillating π state may be characterized by the phase distribution oscillating in a confined region and the phase difference between conformists and contrarians oscillating around π periodically. In addition, we present the parameter space of the oscillating π state and traveling wave state of the model. 相似文献
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The focusing properties of an axicon illuminated by spherical wave are investigated. We define the Fresnel number of the focusing axicon impinged on by spherical wave. The on-axis irradiance distribution versus Fresnel number is studied. It is shown that, similar with the plane wave, focal squeeze, which is defined as deviations for the position of the maximum irradiance, also appears in low Fresnel number. Besides, the on-axis irradiance will be smoothed for appropriate curvature radius of the divergent spherical wave; meanwhile, when the convergent spherical wave is incident on the axicon, the on-axis irradiance varies more seriously. 相似文献