共查询到19条相似文献,搜索用时 109 毫秒
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混浊大气介质调制传递函数的一般特征 总被引:3,自引:2,他引:1
基于混浊介质的调制传递函数(MTF)和在各向同性漫射光源照射下平行平面混浊介质出射光强度分布之间的等效原理,利用辐射传输算法DISORT数值计算了几种典型的均匀大气混浊介质的MTF,获得了整个空间频域内MTF的一般特征.结果显示,大气介质的MTF不但依赖于介质的光学厚度(散射和吸收),也依赖于介质的散射相函数.给出了大... 相似文献
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研制了一种铝靶软X射线源,这种X射线源对轻介质、薄样品的成像更清晰、分辨能力更强。利用多层滤片和生物样品对铝靶软X射线源进行了性能检测,实验显示铝靶软X射线源对轻介质和生物成像具有较高的吸收衬度,成像效果优于其他靶材X射线源,并通过改变工作电压可以显著调节谱线中软X射线的比例。这种铝靶X射线源适合作为实验室便携式软X射线光源。 相似文献
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色散吸收非对称介质光腔中光场的量子理论 总被引:7,自引:2,他引:5
利用格林函数方法对色散吸收介质中的电磁场量子化,研究了由色散吸收介质构成的非对称介质光腔中光场的量子理论,并分析了非对称性对光腔量子性质、工作性能等的影响. 相似文献
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由于大气环境的变化,大气气溶胶污染对光学遥感器成像品质的影响越来越受到载荷研制部门的重视。天基光学遥感系统成像过程中,受到大气气溶胶退化的影响使得光学遥感器成像品质的恶化。大气导致图像质量降低主要原因之一是气溶胶混浊介质引起的前向光散射。根据气溶胶辐射特性,利用混浊介质辐射传输方程,推导了包含气溶胶光学特性的大气点扩散函数模型。根据此模型,定量化分析与评价其对光学遥感器成像的大气模糊效应。研究发现气溶胶介质除了对遥感器成像过程中大气透过率能量衰减影响外,更重要的是由于散射对成像质量产生退化作用,大气气溶胶光学厚度的增加使得气溶胶散射强度的增强,气溶胶光学厚度的变化同样强烈的影响着点扩散函数的空间分布范围,正是因为气溶胶在空间域内对图像产生的退化作用,使得遥感图像质量降低,尤其是图像清晰度的下降。同时,该模型也为遥感图像仿真中,大气链路环节的优化与改进提供了参考依据与模型方法。 相似文献
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散射介质对光的随机散射作用是制约其光学聚焦和成像的重要因素,光学相位共轭技术能够通过对散射光场共轭还原实现透过散射介质的光学聚焦和成像,其中散射光场相位的获取是共轭还原的核心。阐述了偏振相移的基本原理,将偏振相移与相位共轭技术相结合,设计了新的基于偏振相移的数字光学相位共轭系统。采用633 nm的HeNe激光器作为系统光源,毛玻璃作为散射介质开展散射光聚焦实验研究。实验结果表明:该装置能够成功实现透过散射介质的光学聚焦,其中聚焦点与背景光强的比值可达约400倍。 相似文献
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在V型系统中原子相干对吸收—色散关系的影响 总被引:1,自引:1,他引:0
在V型能级系统原子介质中,若利用外场产生相干,则弱光场在该介质中的吸收-色散关系将展现出新的特性.特别是当弱场具有某一特定频率时,介质对光的吸收为零但光折射率大于1. 相似文献
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We report on synthetic aperture microscopy through a highly turbid medium. We first recorded a transmission matrix for the turbid medium with an angular basis of 20,000 complex images covering 0.6 NA. This effectively converts the medium into a lens of the same NA. Distorted images of a target object are then taken at 500 different angles of illumination covering 0.6 NA. For each of the distorted images, the original object image is reconstructed from the transmission matrix by the recently developed turbid lens imaging (TLI) technique. All 500 reconstructed images are synthesized to enhance the NA to 1.2 and thereby generate an object image with twice the enhanced spatial resolution of the individual images. Our method of applying aperture synthesis for TLI makes it possible to enhance the resolving power without increasing the number of transmission matrix elements. This relieves the demand for data acquisition and processing that has impeded the practicality of TLI. 相似文献
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调制传递函数(MTF)定量描述混浊介质对图像质量的影响,它是混浊介质的固有光学特性,利用等效原理可以获得MTF从低频到高频的完整特征.在实际应用中,混浊介质中的图像质量不仅取决于介质的MTF,还与图像的背景辐射密切相关.本文从混浊大气中图像退化机理出发,理论分析了空间频域中天光背景下图像质量的退化过程.参考等效原理,提出了一种考虑天光背景的表观MTF,得到了表观MTF与介质MTF和天光背景的定量关系,从而得到了一种分析背景辐射下混浊介质中图像质量的有效便捷方法.针对图像质量优化方法,从空间频域的角度提出了一种评价原则. 相似文献
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Choi Y Yang TD Fang-Yen C Kang P Lee KJ Dasari RR Feld MS Choi W 《Physical review letters》2011,107(2):023902
We report that disordered media made of randomly distributed nanoparticles can be used to overcome the diffraction limit of a conventional imaging system. By developing a method to extract the original image information from the multiple scattering induced by the turbid media, we dramatically increase a numerical aperture of the imaging system. As a result, the resolution is enhanced by more than 5 times over the diffraction limit, and the field of view is extended over the physical area of the camera. Our technique lays the foundation to use a turbid medium as a far-field superlens. 相似文献
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We present a new method that can provide high resolution images of absolute optical absorption coefficient in heterogeneous turbid media. In this method, acoustic measurements in conventional photoacoustic tomography are combined with diffusing light measurements to separate the product of absorption coefficient and optical fluence or photon density. We validate this method using a series of tissuelike phantom experiments. The experimental results show that targets as small as 0.5 mm in diameter with optical absorption contrasts as low as 1.5 relative to a 50 mm diameter scattering background medium can be clearly detected. 相似文献
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A. Karabutov N. B. Podymova V. S. Letokhov 《Applied physics. B, Lasers and optics》1996,63(6):545-563
The methods of time-resolved laser optoacoustic tomography of inhomogeneous media and related problems are reviewed. Time-resolved laser optoacoustic tomography allows one to measure the distribution of light absorption in turbid media with depth resolution up to several microns in real time. The theory of laser excitation of acoustic waves by absorbing of light in particles, dispersed in transparent, light-absorbing or scattering media, is developed. The distribution of light absorption can be obtained from the temporal course of acoustic pressure. Two schemes of acoustic wave detection — in the medium under testing (direct detection) and in transparent medium, coupled to the investigated one (indirect detection) — are discussed. In both cases the reconstruction of light absorption can be made by simple calculations. Test experiments with homogeneous and layered media confirm the proposed theoretical models and the possibility of using the proposed experimental schemes. Light absorption in homogeneous, inhomogeneous media and in absorbing particles dispersed in turbid media was investigated. The experimental setup allows one to measure the absorption coefficients over the range 1-500 cm–1 with the depth resolution 10–15 m over the depth 1–1.5 mm. 相似文献
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An effective point-spread function (EPSF) for microscopic imaging through turbid media is proposed and calculated. The EPSF incorporates the property of a microscope system as well as the scattering property of a turbid medium. We prove that the image of a thin object embedded in a turbid medium can be expressed by the convolution of the EPSF with an object function. With the help of the convolution relation, image modeling for 5, 000, 000 incident photons can be approximately 15 times faster than the direct Monte Carlo simulation method for a one-dimensional object and can be at least 2 orders of magnitude faster for a two-dimensional object. 相似文献
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A method that uses a Zeeman laser in conjunction with a Glan-Thompson analyzer to image an object in a turbid medium is proposed. A heterodyne signal is generated only when the scattering photons are partially polarized, and the spatial coherence is not seriously degraded after the signal propagates in the turbid medium. A system combining polarization discrimination with optical coherence detection to image the object in a scattering medium is successfully demonstrated. The medium is a solution of polystyrene microspheres measuring 1.072 mum in diameter suspended in distilled water contained in a 10-mm-thick quartz cuvette. The advantages of this optical system, including better selectivity of the weak partially polarized scattering photons and better imaging ability in higher-scattering media, are discussed. 相似文献
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Lev S. Dolin Ekaterina A. Sergeeva Ilya V. Turchin 《Journal of Quantitative Spectroscopy & Radiative Transfer》2012,113(9):691-703
Noisy structure of optical coherence tomography (OCT) images of turbid medium contains information about spatial variations of its optical parameters. We propose analytical model of statistical characteristics of OCT signal fluctuations from turbid medium with spatially inhomogeneous coefficients of absorption and backscattering. Analytically predicted correlation characteristics of OCT signal from spatially inhomogeneous medium are in good agreement with the results of correlation analysis of OCT images of different biological tissues. The proposed model can be efficiently applied for quantitative evaluation of statistical properties of absorption and backscattering fluctuations basing on correlation characteristics of OCT images. 相似文献
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Two-wave mixing in a dynamic holographic film acts as the adaptive beam combiner in a short-coherence interferometer that performs optical coherence-domain reflectometry (OCDR) through turbid media. This approach combines the high spatial resolution and sensitivity of coherence-domain reflectometry with photorefractive quantum-well-based adaptive homodyne detection. A depth resolution of 28 microm and penetration through 16 mean free paths in a turbid medium have been obtained in this adaptive OCDR application. 相似文献