共查询到20条相似文献,搜索用时 109 毫秒
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基于高斯谢尔光束的相干模式分解理论和波动光学,建立了部分相干同步辐射硬X射线光束通过光学器件的传播模型。模拟了微聚焦X射线光束照射下光栅的分数塔尔博特效应,得到了聚焦光束的光强分布和相干特性变化,并分析了散焦光束入射下的光栅自成像。然后通过模拟准直光束入射下的光栅塔尔博特效应,得到了不同传播距离处自成像条纹的变化情况,分析了影响光栅自成像条纹形状的因素。通过光栅衍射条纹测量同步辐射相干度,发现对矩形相位光栅来说,应该对衍射图样进行傅里叶分解,求出各级傅里叶系数随传播距离的变化曲线,从而得到入射光束相干特性。 相似文献
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有限宽光束在生物组织中传输的蒙特卡罗方法 总被引:1,自引:0,他引:1
基于光在生物组织中的传输理论,研究有限宽光束在生物组织中的传输特性.利用入射光强与格林函数进行卷积计算,推导了有限宽光束在圆柱坐标系下的光传输过程,给出了有限宽光束的光传输方程.以高斯光源和平圆光源为例,进一步给出了两种光源的有限宽光束在生物组织中的光传输方程.介绍了Monte Carlo方法原理及模拟光在多层生物组织中的传输过程.给出了典型三层生物组织的散射系数、吸收系数和折射率等光学参数.利用Monte Carlo方法模拟了有限宽光束在三层生物组织中的传输特性,对比研究了高斯光源和平圆光源有限宽光束在三层生物组织传输时光学参数漫透射率、漫反射率和光能流率的变化规律.这些参数的变化规律可为光在生物组织传输的实际应用提供理论指导. 相似文献
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轴棱锥——透镜系统的光束传输与变换 总被引:4,自引:1,他引:3
对平面波经过轴棱锥--透镜系统的整个演绎过程进行详细的理论分析,数值模拟和实验验证.平面波经过轴棱锥产生横向光场不变的近似无衍射光,在最大无衍射距离内加入合适透镜将产生局域空心光束(Bottlebeam),而空心光束的尺寸可通过改变透镜焦距进行控制.当光束继续传播,贝塞尔(Bessel)光发生自重建(Self-reconstruction),但重建的Bessel光将会发散,光强随着传播距离增大而迅速下降,且中心亮斑尺寸也迅速增大.通过引入另一聚焦透镜对光束进行修正,恢复了Bessel光束的无衍射的特性.利用显微镜-CCD光束分析系统获得不同传播距离的截面光强分布,实验结果和理论分析及数值模拟相吻合. 相似文献
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《光学学报》2016,(3)
传统的漫射方程均假设生物组织在纵向上是半无限厚的,横向上是无限大的。针对某些在横向上不是无限大的生物组织(如前臂和手指),建立了一个任意多层矩形生物组织漫射模型,该模型假设生物组织在纵向上是半无限厚的、多层的,在横向上是个矩形。在矩形边界条件下,根据光在生物介质中传播的漫射方程,结合外推边界条件,建立并给出了光在半无限厚稳态多层矩形介质中的漫射方程的精确解,利用建立的模型计算了空间分辨漫反射,同时编写相应的蒙特卡罗模拟程序,验证方程的正确性。建立的方程不但能解决横向上是矩形的介质问题,还能解决横向上无限大、纵向上半无限厚的介质问题,更能解决在横向上x或y轴之一是无限大、另一个轴是有限大小的组织问题。 相似文献
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光在苹果组织中传输的光谱特性 总被引:1,自引:0,他引:1
用M onte-Carlo方法模拟研究了激光波长632 nm与750 nm的高斯光束在苹果组织中传输的吸收、散射光谱特性。结果表明:高斯光束特殊的能量分布特性对激光在苹果组织中的传播有重要的影响,苹果组织对750 nm激光的反射、吸收、透射都较低,有更多的光子在组织内部与组织相作用,能够更清楚的反映组织内部信息。因此,在生物组织中近红外光波的传输性比较好,便于应用于研究生物组织。 相似文献
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利用蒙特卡罗方法模拟了半无限大生物组织内部深度分辨的光能流率的分布情况。分析了漫射近似理论的有效使用范围。当组织厚度大于 3/ 2个光子的平均自由程时 ,应用漫射近似理论能得到很好的结果 ,反之 ,漫射理论不能使用。也就是说 ,当组织厚度z >0 1875cm时 ,应用漫射理论能得到很好的结果 ;当组织厚度z <0 1875cm时 ,漫射理论不能使用 相似文献
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Spies M 《Ultrasonics》2007,46(2):138-147
The Gaussian beam (GB) superposition approach can be applied to model ultrasound propagation in complex-structured materials and components. In this article, progress made in extending and applying the Gaussian beam superposition technique to model the beam fields generated by transducers with flat and focused rectangular apertures as well as with circular focused apertures is addressed. The refraction of transducer beam fields through curved surfaces is illustrated by calculation results for beam fields generated in curved components during immersion testing. In particular, the following developments are put forward: (i) the use of individually determined sets of GBs to model transducer beam fields with a number of less than ten beams; (ii) the application of the GB representation of rectangular transducers to focusing probes, as well as to the problem of transmission through interfaces; and (iii) computationally efficient transient modeling by superposition of ‘temporally limited’ GBs. 相似文献
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Xichang Wang Xiancheng Wu Shumei Wang 《International Journal of Infrared and Millimeter Waves》2007,28(1):51-59
The infrared ray propagation model of finite size flat beam in biological tissue is set up. Gaussian beams and circularly
flat beams were compared. The model is simulated with Monte Carlo method, and the influence of parameters of biological tissue
and properties is analyzed. The potential application of the model is demonstrate by estimating the absorption and transport-corrected
scattering coefficients from reflectance measured from intact tissue. 相似文献
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Based on the vectorial Rayleigh diffraction integral and the hard-edge aperture function expanded as the sum of finite-term complex Gaussian functions, an approximate analytical expression for the propagation equation of vectorial Gaussian beams diffracted at a circular aperture is derived and some special cases are discussed. By using the approximate analytical formula and diffraction integral formula, some numerical simulation comparisons are done, and some special cases are discussed. We find that a circular aperture can produce the focusing effect but the beam becomes the shape of ellipse in the Fresnel region. When the Fresnel number is equal to unity, the beam is circular and the focused spot reaches a minimum. 相似文献
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An alternative theoretical model called circular partially coherent flattened Gaussian beam (FGB) is developed to describe a circular partially coherent beam with a flat-topped spatial profile. Explicit expression for the propagation factor of a circular partially coherent FGB is derived. We drive the analytical formulae for the cross-spectral density and mean-squared beam width of a circular partially coherent FGB propagating through a paraxial ABCD optical system based on the generalized Collins formula. The intensity, spreading and directionality properties of a circular partially coherent FGB propagating in free space are studied as numerical examples. The propagation properties of a circular partially coherent FGB agree well with those of a partially coherent flat-topped beam reported in the literature. Thus, our model provides an alternative but reliable model for describing a circular partially coherent beam with flat-topped profile. 相似文献
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Profile shaping of a Gaussian laser beam by an acoustic wave is well described using Collins integral and ABCD matrix formalism. It is shown by a numerical simulation that the relative width of the laser beam to the ultrasonic wavelength and the acoustic pressure inside the acoustooptic cell act on the light intensity diffraction pattern.Obtained results show that the output intensity profile differs from the incident Gaussian beam shape, and it is more broadened with an increase in the acoustic pressure. The intensity of a focused laser beam is transformed in a flat form in the central region if the acoustic pressure is proprely controlled.On the other hand the intensity longitudinal range (ILR) of the flat shape is discussed along the propagation axes, we have found the ILR is about 2 mm for a focal length distance f=100 mm. 相似文献
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Yangjian Cai Q. Lin H. T. Eyyubo?lu Y. Baykal 《Applied physics. B, Lasers and optics》2009,94(2):319-325
The propagation of an elliptical Gaussian beam (EGB) through an astigmatic ABCD optical system in a turbulent atmosphere is
investigated. An analytical formula for the average intensity of an EGB and a generalized tensor ABCD law for the generalized
complex curvature tensor are derived. As an application example, we derived an analytical formula for the average intensity
of an elliptical flat-topped beam propagating through an astigmatic ABCD optical system in a turbulent atmosphere. As a numerical
example, the focusing properties of an EGB focused by a thin lens in a turbulent atmosphere are studied. It is found that
the focused beam at the focal plane becomes a circular Gaussian beam when the atmospheric turbulence is strong enough, and
the beam width of the circular Gaussian beam is determined by atmospheric turbulence strength, focal length of the thin lens,
and wavelength of the initial beam but is independent of the initial beam widths (i.e., initial intensity distribution). 相似文献
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Zhangrong Mei 《Optics Communications》2011,284(22):5248-5252
The focal shifts of focused truncated random electromagnetic beams are investigated. Based on the complex Gaussian expansion method for a hard-edged aperture function, the analytical propagation formula of cross-spectral density matrix for a random electromagnetic beam focused by an optical system with a thin lens and a circular aperture is derived. The Fresnel numbers related with the beam and system parameters are defined and used to examine focal shifts. The dependence of the focal shifts on the different Fresnel numbers and polarization distribution are discussed in detail with numerical examples. 相似文献
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Kamakura T Ishiwata T Matsuda K 《The Journal of the Acoustical Society of America》2000,107(6):3035-3046
A model equation that describes the propagation of sound beams in a fluid is developed using the oblate spheroidal coordinate system. This spheroidal beam equation (SBE) is a parabolic equation and has a specific application to a theoretical prediction on focused, high-frequency beams from a circular aperture. The aperture angle does not have to be small. The theoretical background is basically along the same analytical lines as the composite method (CM) reported previously [B. Ystad and J. Berntsen, Acustica 82, 698-706 (1996)]. Numerical examples are displayed for the amplitudes of sound pressure along and across the beam axis when sinusoidal waves are radiated from the source with uniform amplitude distribution. The primitive approach to linear field analysis is readily extended to the case where harmonic generation in finite-amplitude sound beams becomes significant due to the inherent nonlinearity of the medium. The theory provides the propagation and beam pattern profiles that differ from the CM solution for each harmonic component. 相似文献