共查询到20条相似文献,搜索用时 28 毫秒
1.
Jakob J. Stamnes 《Optics Communications》2009,282(12):2286-19414
We derive explicit formulas for the focal shift, the intensity increase, and the axial zeros obtained on focusing at low Fresnel numbers through a plane interface between two isotropic media, and demonstrate their validity through comparisons with numerical plots of axial intensity distributions. Also, we show that for the special case in which the two isotropic media have the same refractive index, these formulas are in complete agreement with previous results presented for focusing in a single medium. 相似文献
2.
基于部分相干光的传输理论,研究了部分相干平顶高斯光束通过球差透镜聚焦后轴上点的光强分布。数值计算表明:轴上最佳聚焦点随着球差从负到正的变化而向几何焦点方向移动;光束阶数越大,实现最佳聚焦点越过几何焦点所需的正球差值越小;正负球差对应的最佳聚焦点始终分居于无球差时最佳聚焦点的两侧;轴上最佳聚焦点的光强随着球差从负到正的变化而变小;当正负球差绝对值较大时,光强随球差的变化较为缓慢,而在球差值为0附近,光强随球差的变化比较剧烈。 相似文献
3.
M. Bondani A. Allevi G. Zambra A. Andreoni J. Peřina J. Křepelka J. Peřina Jr. 《The European physical journal. Special topics》2008,160(1):33-41
Twin-beam states of light produced by spontaneous parametric downconversion are endowed with sub-shot-noise photon-number
correlations at any intensity regime. We have demonstrated sub-shot-noise photon-number correlations in a ps-pulsed intense
(more than 1000 photons) twin beam by measuring the variance of the difference in the number of photons detected in the two
outputs of the crystal. The variance is 3.25 dB below the shot-noise level. Measurements show that detection of sub-shot-noise
correlation requires a careful selection of twin coherence areas and that these areas depend on the pump intensity. 相似文献
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5.
Romeric Pobre 《Optics Communications》2006,267(2):295-304
We calculate the radiation force that is exerted by a focused continuous-wave Gaussian beam of wavelength λ on a non-absorbing nonlinear particle of radius a ? 50λ/π. The refractive index of the mechanically-rigid particle is proportional to the incident intensity according to the electro-optic Kerr effect. The force consists of two components representing the contributions of the electromagnetic field gradient and the light scattered by the Kerr particle. The focused intensity distribution is determined using expressions for the six electromagnetic components that are corrected to the fifth order in the numerical aperture (NA) of the focusing objective lens. We found that for particles with a < λ/21.28, the trapping force is dominated by the gradient force and the axial trapping force is symmetric about the geometrical focus. The two contributions are comparable with larger particles and the axial trapping force becomes asymmetric with its zero location displaced away from the focus and towards the beam propagation direction. We study the trapping force behavior versus incident beam power, NA, λ, and relative refractive index between the surrounding liquid and the particle. We also examine the confinement of a Kerr particle that exhibits Brownian motion in a focused beam. Numerical results show that the Kerr effect increases the trapping force strength and significantly improves the confinement of Brownian particles. 相似文献
6.
采用变焦液体透镜的共焦检测系统的设计与仿真 总被引:1,自引:0,他引:1
共焦显微技术越来越广泛地应用于微机电系统和半导体器件的三维轮廓测量。设计一种新型采用变焦透镜作为轴向扫描方式的共焦显微系统,利用变焦透镜的焦距变化来代替传统的轴向位移扫描。系统实现了无机械运动的轴向扫描,消除了传统共焦系统中由位移台移动带来的振动,不仅减小了系统的复杂度,而且降低了成本。进一步设计了基于位移台和变焦透镜的两种共焦检测系统,并且对其进行了仿真实验。实验结果表明:基于位移台和基于变焦透镜的共焦系统的聚焦成像和离焦成像结果类似,并且光强的轴向分布曲线也基本相同,表明此方法可行。 相似文献
7.
We discover that the slight transverse offset of a point detector results in a shift of the axial intensity response curve in a dual-axes confocal microscopy (DCM). Based on this, we propose a new dual-axes differential confocal microscopy (DDCM) with high axial resolution and long working distance, in which two point detectors are placed symmetrically about the collection axis. And a signal is obtained through the differential subtraction of two signals received simultaneously by the two point detectors. Theoretical analyses and preliminary experiments indicate that DDCM is feasible and suitable for the high precision tracing measurement of microstructures and surface contours. 相似文献
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9.
用矢量衍射方法分析了线偏振光入射到带有三环位相型光瞳滤波器的高数值孔径物镜时,焦点的轴向和横向光强分布.数值模拟结果表明,高数值孔径物镜聚焦时需同时考虑光强的轴向和横向分布.通过加入三环位相光瞳滤波器,在实现横向超分辨的同时实现了光学系统轴向焦深扩展和轴向光强分布平坦化,并且位相调制深度变化时,会出现轴向焦移现象.对三环位相光瞳滤波器结构进行了优化,得出了优化结果.
关键词:
光学超分辨
扩展焦深
位相型光瞳滤波器
矢量衍射方法 相似文献
10.
Appearance of anterior cruciate ligament autografts in their tibial bone tunnels on oblique axial MRI. 总被引:4,自引:0,他引:4
The objective of this study was to observe the changing appearance of human anterior cruciate ligament (ACL) grafts in their tibial bone tunnels by MRI using oblique axial images. One-hundred and eight knees in 75 patients were studied by MRI at 1-33 months after arthroscopic ACL reconstructions using double-looped, autogenous semitendinosus and/or gracilis tendons. Knees with poor stability were excluded from this study. The examinations were performed at 0.2T with spin echo proton density and T2-weighted oblique axial images. Appearances of grafts were mainly described on spin echo proton density images based upon time after surgery. The grafts appeared as homogeneous, low signal intensity areas in the bone tunnels at 1 month after the surgery. Ring-shaped low signal intensity areas were observed along the wall of the bone tunnels in the 2- to 3-month group. In many grafts from this group, each tendinous bundle appeared as a low signal area separated by a high signal intensity area. In all cases in the 4- to 6-month group, the thickness of the ring-shaped low signal intensity area had increased, whereas the thickness of the high signal intensity area had decreased. In almost all of the cases, the interior of the bone tunnel gradually became a homologous low signal intensity region by 7 to 12 months after the surgery. According to these results, it is suggested that the maturation of the tendon-bone interface was completed from 6 to 12 months after the ACL reconstruction. 相似文献
11.
Dikanov SA Tyryshkin AM Bowman MK 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2000,144(2):228-242
The cross-peak intensity for a S = 1/2, I = 1/2 spin system in two-dimensional HYSCORE spectra of single-crystals and powders is analyzed. There is a fundamental difference between these two cases. For single crystals, the cross-peak intensity is distributed between the two (+, +) and (+, -) quadrants of the hyperfine sublevel correlation (HYSCORE) spectrum by the ratio c(2):s(2) (C. Gemperle, G. Aebli, A. Schweiger, and R. R. Ernst, J. Magn. Reson. 88, 241 (1990)). However, for powder spectra another factor becomes dominant and governs cross-peak intensities in the two quadrants. This factor is the phase interference between modulation from different orientations of the paramagnetic species. This can lead to essentially complete disappearance of the cross-peak in one of the two (+, +) or (+, -) quadrants. In the (+, +) quadrant, cross-peaks oriented parallel to the main (positive) diagonal of the HYSCORE spectrum are suppressed, while the opposite is true in the (+, -) quadrant where cross-peaks nearly perpendicular to the main (negative) diagonal of HYSCORE spectra are suppressed. Analytical expressions are derived for the cross-peak intensity profiles in powder HYSCORE spectra for both axial and nonaxial hyperfine interactions (HFI). The intensity is a product of two terms, one depending only on experimental parameter (tau) and the other only on the spin Hamiltonian. This separation provides a rapid way to choose tau for maximum cross-peak intensity in a region of interest in the spectrum. For axial HFI, the Hamiltonian-dependent term has only one maximum and decreases to zero at the canonical orientations. For nonaxial HFI, this term produces three separate ridges which outline the whole powder lineshape. These three ridges have the majority of the intensity in the HYSCORE spectrum. The intensity profile of each ridge resembles that observed for axial HFI. Each ridge defines two principal values of the HFI similar to the ridges from an axial HFI. 相似文献
12.
Combining differential confocal microscopy and an annular pupil filter, we obtained the normalized axial intensity distribution curve of an optical system. We used the sharp slopes of the axial response curve of the optical system to measure the surface profile of a reflection grating. Experimental results prove that this method can extend the axial dynamic range and improve the transverse resolution of three-dimensional profilometry by sacrificing axial resolution. 相似文献
13.
用Langmuir探针对射频(13.56 MHz)感应等离子体进行了诊断,给出了Ar等离子体轴向和径向参数随气压的变化。采用发射光谱测量了等离子体中氩原子的750.3nm谱线强度随气压在轴向的变化,其变化趋势与Langmuir探针测量结果的变化趋势相一致。测量了氩离子的434.8nm谱线强度随气压在轴向的变化并获得了氩离子的434.8nm谱线强度与氩原子的430.0nm谱线强度的比值在轴向三个不同位置的变化。从测得的结果可知:在放电室中上部形成了均匀稳定的高密度等离子体,在靶附近有所降低,在中部以下等离子体密度逐渐变低;在径向6~7 cm以内的区域等离子体参数变化不大,形成了均匀稳定的等离子体,等离子体参数在器壁处变化明显。 相似文献
14.
We address the effect of the truncation parameter and spherical aberration (SA) on the singularity transformation and spectral behavior of the polychromatic Gaussian beams focused by an aperture lens with SA in detail. The numerical simulation results, based on the derived equations of the intensity and the spectral density, are given. It is found that the axial singularities vanished with the change of the truncated parameter. The intensity and drastic spectral change fade away with an annihilation process of the phase singularities, and the drastic spectral change does not disappear immediately at the moment the phase singularity annihilates. The singularities in the focal region will redistribute with the increment of SA coefficient, some singularities will vanish, some will spilt into two new singularities, and other off-axial singularities will appear and split into two new singularities as well. When SA coefficient changed, we can find that the axial singularities disappear as well with the decreasing value of truncation parameter. These new splitted singularities due to the change of SA coefficient will converge into one singularity again and disappear gradually. 相似文献
15.
Based on the beam model for the flattened multi-Gaussian beams (FMGBs) with an axial shadow and partially coherent theory, the expression for cross-spectral density of partially coherent FMGBs with an axial shadow has been given, and the analytical expression for the spectral intensity of partially coherent FMGBs with an axial shadow passing through paraxial ABCD optical systems has been derived. The spectral shift of partially coherent FMGBs with an axial shadow focused by a thin lens has been analyzed quantitatively. The effects of the beam profile, spatial coherence parameter and the system parameters on the relative spectral shift have been discussed in detail. Our results show that the spectral intensity and the spectral shift of partially coherent FMGBs with an axial shadow passing through paraxial ABCD optical systems depend on the source spectral density, the generalized Fresnel number of the system, the transverse coordinate, the spatially coherence parameter, as well as the beam orders. 相似文献
16.
用3维时域有限差分方法分别研究了在355 nm入射激光作用下, 熔石英后表面具有不同形状 和位置的断点划痕对场分布的影响.研究表明,对于椭圆状的坑点, 当共线的轴长逐渐 增大时, 电场幅值与强点数目先增大后减小, 获得最大光强增强因子的两轴 比是1.1-1.2, 此时坑点呈近圆形. 当平行的轴长逐步增大时,电场幅值先逐渐增大, 当两轴比为0.53时趋于平缓, 而强点总数则呈"J"形曲线不断增长. 当坑点尺寸相同 但排放位置不同时, 相邻坑点的相对面积愈大, 调制愈强. 相似文献
17.
阐述了GS算法用于相位恢复的原理,并对算法的应用范围进行了扩展,不再局限于已知光瞳面和焦平面光强的情况。仿真中,选取了光束自由传输的两个垂轴截面,利用光强分布,采用了GS迭代算法对常见的几种波前畸变进行了恢复。针对相位恢复中GS算法收敛速度慢和精度低的问题,提出了迭代过程中,在光束输入端和输出端分别进行加权改进,给出了加权系数取值范围。仿真结果表明,这种改进有利于算法跳出局部极值,在加权值取1.2时,针对象散像差的恢复中,速度和精度提高了2倍左右,对一些其它常见像差的恢复精度也有所提高。 相似文献
18.
探头对共聚焦内窥成像系统层析能力的影响 总被引:2,自引:1,他引:1
根据透镜成像规律和单模光纤的传输特性,获得基于单模光纤的共聚焦内窥成像系统轴向光强分布,发现系统的成像过程由于单模光纤的介入呈现非线性,照明光路系统和接收光路系统仅影响系统接收信号的总强度,系统层析能力取决于探头和单模光纤性能.通过建立的共聚焦内窥成像实验装置,测量出在三组不同物镜组合情况下系统的归一化轴向光强分布.结果显示已建立的共聚焦内窥成像系统的理论模型是正确的,扫描光点的定位精度对系统层析能力影响很大,系统设计应该综合考虑光学、机械和电子方面的性能要求. 相似文献
19.
Homma M. Somei H. Niwa Y. Yokokura K. Ohshima I. 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》1999,27(4):961-968
Our new vacuum arc control technology SADE doubles the high current interruption capability of our conventional axial magnetic field technology. First, we describe the vacuum arc motion behavior recorded by a high speed charge-coupled device video camera. This arc behavior is closely related to axial magnetic field intensity. In particular, it depends on the profile of the externally generated axial magnetic field. The anode spot is likely to move to the highest magnetic field intensity. Second, we describe analytical results for concentration of vacuum arc at the anode side contact surface. This analysis implies the possibility of an ideal magnetic field profile and intensity for vacuum arc control. Finally, we describe experimental results for vacuum arc control compared with the physical and theoretical results mentioned above, and we show a practical electrode configuration for vacuum interrupters and its application in a high current interruption experiment 相似文献
20.
基于非线性薛定谔方程,采用分步傅里叶算法模拟了方形超高斯光束在Kerr介质中的传输情况,重点分析了方形超高斯光束轴向中心强度与对角方向强度的演化特性,同时还分析了其在Kerr介质中的自聚焦特性、峰值光强变化情况以及B积分变化情况。研究结果表明:方形超高斯光束通过Kerr介质后,距光束中心不同距离处有不同程度的强度增强和凹陷,光束中心附近的强度增强和凹陷较弱,光束边缘以及四角处的强度增强和凹陷较强,且对角方向上的强度增强和凹陷程度要强于轴向中心方向;减小阶数可以减缓光束的边缘强度增强,并可以减缓B积分的增长;减少Kerr介质厚度可以降低光束边缘强度增强程度,并可以减小B积分的大小。提出了光束边缘强度起伏的主要原因可能是光束的相干叠加。 相似文献