基于数字微镜器件超像素法实现散射介质传输矩阵的自参考干涉测量

散射介质的传输矩阵系统描述了散射介质对输入与输出光场之间的变换关系,是研究与控制光在无序介质中传输特性的重要工具.本文使用数字微镜器件实现散射介质传输矩阵的自参考干涉测量,首先利用超像素法实现对入射光的复振幅调制获得同时包含参考光和信号光的复合场,进而基于四步相移法分别测量了散射介质在Hadamard基和轨道角动量(OAM)基下的传输矩阵.进一步,根据相位共轭原理实现了光透过散射介质后的单点聚焦、多点聚焦以及涡旋聚焦,验证了传输矩阵测量的准确性.该方法能够有效提高光场调制的自由度,实现散射介质传输矩阵的测量,对散射环境下的光学成像和光通信等具有潜在应用价值.     

利用受激布里渊散射改善偏振抽取腔光束质量的研究

在理论上分析了受激布里渊散射相位共轭效应和阈值效应对后向受激布里渊散射光束发散角的影响。在实验上，用受激布里渊散射相位共轭镜（SBS PCM）代替普通反射镜构成Nd:YAG激光器的偏振抽取腔，补偿了激活介质和光学元件造成的波前畸变，压缩了发散角，改善了光束质量。研究了抽运能量、透镜焦距等因素对受激布里渊散射偏振抽取腔输出光光束质量的影响。     

散射介质超衍射极限技术研究进展

综述了已有散射介质超衍射极限聚焦和成像技术的研究现状及进展。首先介绍了这一领域的研究背景及意义,以及已有超衍射极限成像技术的发展现状;然后给出了应用于超衍射极限成像的散射介质定义;其次分析了时间反演技术在声学、微波领域聚焦上的应用,介绍了时间反演法在光学领域超衍射极限聚焦应用中的实现方法,总结了散射介质加入到光学系统中的作用,分析了利用反馈控制调节和光学相位共轭方法进行散射介质超衍射极限聚焦方法的特点;讨论了基于空域和空频域传输矩阵测量的散射介质宽场成像方法及在该目的下的散射介质制备方法;最后给出了散射介质光学超衍射极限成像技术研究前景及展望。     

散射介质超衍射极限技术研究进展

综述了已有散射介质超衍射极限聚焦和成像技术的研究现状及进展。首先介绍了这一领域的研究背景及意义,以及已有超衍射极限成像技术的发展现状;然后给出了应用于超衍射极限成像的散射介质定义;其次分析了时间反演技术在声学、微波领域聚焦上的应用,介绍了时间反演法在光学领域超衍射极限聚焦应用中的实现方法,总结了散射介质加入到光学系统中的作用,分析了利用反馈控制调节和光学相位共轭方法进行散射介质超衍射极限聚焦方法的特点;讨论了基于空域和空频域传输矩阵测量的散射介质宽场成像方法及在该目的下的散射介质制备方法;最后给出了散射介质光学超衍射极限成像技术研究前景及展望。     

相干光经过不透明散射介质的聚焦

由于散射介质的散射特性,入射光通过散射介质后相干性受到破坏形成散斑场,使得传统光学成像系统无法聚焦探测内部物体的信息。根据波前整形原理,通过反馈优化算法调控入射光束的相位,在目标位置处将散斑调制为聚焦光斑,光强增强。基于此方法,在实验上搭建实验平台,对空间光调制器(SLM)的每个像素加载系列等间隔相位,一次采集多幅散斑图像,应用局部最大优化算法实现对光束任意点聚焦,并提出了一种得到不同大小区域的均匀的聚焦光斑的新方法,为实现聚焦平面内的目标成像提供了新思路。     

基于深度学习的透过散射介质偏振识别

当偏振光在散射介质中传播时,由于散射粒子的多重散射作用而造成偏振信息的扰乱和丢失.为了保证偏振信息在散射介质中高效和高保真的传输,提出一种基于深度学习的透过散射介质偏振识别方法.通过构建卷积神经网络来提取散斑光强信息中入射光波偏振信息的特征,实现对入射光波偏振态的高分辨率识别,并使用初始相位不同的偏振光来验证卷积神经网络对偏振态识别的鲁棒性.实验结果表明,所提方法具有识别速度快和准确率高的优点,理论上可以通过无限大的数据来训练神经网络,因此该方法在偏振光学成像和激光通信等领域具有巨大的应用潜力.     

激光通过不同厚度的强散射介质的聚焦

通常情况下,激光光束经过散射介质后会产生无序的散斑。基于波前相位调制技术,利用连续序列算法结合四步相移法对入射激光的波面进行相位调制,使其通过散射介质在目标位置处形成聚焦。实验着重研究激光经过不同厚度的强散射片样品的聚焦,讨论散射介质的厚度与聚焦点光强增长因子的关系。实验结果表明,透过的散射介质越厚,聚焦光斑尺寸越小,目标位置处聚焦点的光强增长因子也越小。     

混浊介质二维后向漫散射穆勒矩阵的测量

研制了一套实验系统用于测量混浊介质的后向漫散射穆勒矩阵.在系统中，激光被调制成所需偏振态，聚焦于混浊介质表面.利用CCD相机配合相应的偏振元件，测量入射点周围区域的后向散射光中特定偏振态的能量空间分布，并由测量值计算出介质的后向漫散射穆勒矩阵.描述了系统的组成、测量原理以及方法，分别测量了消偏振分光棱镜的反射穆勒矩阵和浓度1.5％的脂肪乳溶液的后向漫散射穆勒矩阵.实验证明:该系统能够完全消除样品表面镜面反射光的干扰，精确的测量混浊介质的后向漫散射穆勒矩阵；并可望用于生物组织的研究中.     

基于频谱信息的浑浊水下偏振成像技术

水体中悬浮粒子对光的散射导致浑浊水下成像质量下降。偏振光学成像技术可基于偏振信息分离散射光和信号光,是浑浊水下成像的有效方法。然而,现有的水下偏振成像技术主要从空域分离散射光和信号光,对于散射光的抑制效果较为有限。利用散射光和信号光在频域的差异性,基于对偏振图像频谱信息的处理实现了对后向散射光的有效抑制,从而实现了成像清晰度的显著提升。在不同浑浊程度水体环境下对于不同物体开展了多组实验,实验结果表明,所提方法相对于传统的水下偏振成像方法可更好地抑制后向散射光和凸显物体信号光,最终实现在浑浊水体环境下的清晰成像,尤其对于高浑浊水体,成像清晰度提升效果明显。     

透过散射介质对直线运动目标的全光成像及追踪技术

光散射是限制光传输以及降低和破坏光学成像性能的主要因素,透过复杂散射介质对运动目标的全光成像是光学领域极具挑战性的技术之一.本文提出一种利用散斑差值自相关透过散射介质对运动目标进行实时追踪的方法.采用赝热光照明,基于光学记忆效应理论,通过对运动目标采集的两帧散斑做差值,然后做自相关运算,计算目标移动的距离,实现对目标的实时追踪,并且利用相位恢复算法进行简单处理就可以重建隐藏目标.对该方法进行了实验验证,成功地对隐藏的运动目标实现了成像与追踪.这种透过散射介质对运动目标的全光成像及实时追踪技术,在生物医学等领域具有重要应用潜力.     

Imaging and multiple scattering through media containing optically active particles

This paper examines the behaviour of polarized light scattered by a medium containing small chiral spheroidal particles. We show that for single scattering the observed phenomena of optical activity may be interpreted in terms of an averaged Mueller matrix and describe how the degree of polarization is affected by such a medium. The polarization properties of multiply scattered light by chiral particles are considered through the use of Monte Carlo simulations. It is shown that the effects of chirality under multiple scattering can be interpreted as an order-preserving influence in a disordered system and that this influence can, in principle, be exploited for the purposes of imaging.     

Imaging and multiple scattering through media containing optically active particles

Abstract

This paper examines the behaviour of polarized light scattered by a medium containing small chiral spheroidal particles. We show that for single scattering the observed phenomena of optical activity may be interpreted in terms of an averaged Mueller matrix and describe how the degree of polarization is affected by such a medium. The polarization properties of multiply scattered light by chiral particles are considered through the use of Monte Carlo simulations. It is shown that the effects of chirality under multiple scattering can be interpreted as an order-preserving influence in a disordered system and that this influence can, in principle, be exploited for the purposes of imaging.     

Memory effect evaluation based on transmission matrix calculation

The memory effect is a type of auto correlation observed in linear systems, which is widely used to control scattered light through thin scattering layers.We show that there exists a strong correlation among the optimized phase distributions of adjacent focal points in focusing through scattering media.The numeric simulation and experiment indicate that within the memory effect, the phase difference between the two adjacent focal points shows an optical phase fringe pattern, and the closer the adjacent focal points are, the wider the fringe pattern will be, corresponding to the tilting of a plane wave phase added onto the acquired optical phase distribution at the focal point.This effect can be utilized for achieving optimal phase distributions of focal point scanning without optical phase evaluation via the experiment, which has great potential application in imaging through the scattering medium.     

Time reversal versus phase conjugation in a multiple scattering environment

We present experimental results on the reversibility of ultrasound in a multiple scattering medium. An ultrasonic pulsed wave is transmitted from a point source to a 128-element receiving array through 2D samples with various thickness. The samples consist of random collections of parallel steel rods immersed in water. The scattered waves are recorded, time reversed and sent back into the medium. The time-reversed waves are converging back to their source and the quality of spatial and temporal focusing on the source is related to the second-order moments of the scattered wave (correlation) in time and in space. Experimental results show that it is possible to obtain a robust estimation of the correlations on a single realisation of disorder, taking advantage of the wide frequency bandwidth. The spatial resolution of the system is only limited by the correlation length of the scattered field, and no longer by diffraction. Moreover, successful time-reversal focusing using a single element instead of an array is possible, whereas a one-channel monochromatic phase conjugation fails. The efficiency of broad-band time reversal compared to monochromatic phase conjugation lies in the number of 'information grains' in the frequency bandwidth.     

High reflectivity phase conjugation in magnetized diffusion driven semiconductors

Optical phase conjugation via stimulated Brillouin scattering (OPC-SBS) in magnetized diffusion driven semiconductors under the off-resonant transition regime has been investigated theoretically. The model is based upon the coupled-mode approach and incorporates the effect of pump absorption through the first-order induced polarization. The linear dispersion is found not to affect the reflectivity of the phase conjugate Stokes shifted Brillouin mode. The reflectivity of the image radiation is dependent upon the Brillouin susceptibility and can be significantly enhanced through n-type doping of the crystal and the simultaneous application of magnetic field. Moreover, the threshold of the pump intensity required for the occurrence of SBS in the crystal with finite optical attenuation can be considerably diminished through a suitable choice of the excess carrier concentration and the magnetic field. Consequently, OPC-SBS becomes a possible tool in phase-conjugate optics even under not-too-high power laser excitation by using moderately doped n-type semiconductors kept under the influence of magnetic field. Numerical estimates made for n-InSb crystal at 77 K duly irradiated by nanosecond pulsed 10.6 μm CO₂ laser show that high OPC-SBS reflectivity (70%) can be achieved at pump intensities below the optical damage threshold if the crystal is used as an optical waveguide with relatively large interaction length (L ∼5 mm) which proves its potential in practical applications such as fabrication of phase conjugate mirrors.     

A phase sensitive optical rotation measurement in a scattered chiral medium using a Zeeman laser

A novel circular polarized optical heterodyne interferometer using a Zeeman laser to measure optical rotation both in nonscattered and scattered chiral medium is proposed. A pair of correlated orthogonal circular polarized light waves of different temporal frequency propagating in the chiral medium at different speed is studied. This results in phase retardation between circular polarized light waves of which the phase difference is proportional to the optical rotation angle of a linear polarized light in a chiral medium. In the mean time, two orthogonal circular polarized light waves can be treated as a circular polarized photon pair that is able to reduce the scattering effect in a scattered chiral medium. Then the optical rotation angle can be measured in the scattering medium. In addition, a common-path configuration with respect to circular polarized light waves immune the background noise. This further improves the sensitivity on optical rotation measurement based on phase difference detection.     

Polarization visualization of scattering media with CW laser radiation

The method of polarization visualization of a multiply scattering medium containing macroinhomogeneities based on analysis of polarization spatial distribution of a scattered linearly polarized light is discussed. The treatment is based on statistical properties of the effective optical path distribution of scattered field components. The influence of media scattering properties and the geometry of the experiment on the inhomogeneity image contrast obtained with use of polarization degree and of normalized scattered intensity of radiation as visualization parameters are discussed, as well as spatial resolution achieved in these both cases. Using the results of theoretical analysis and of the experimental model, the relationship between the shapes of spatial distributions of polarization degree and the intensity of the scattered light is considered as a function of the position of the visualized object (an absorbing half-plane immersed in a plane layer of the scattering medium). The opportunities for enhancing the quality of the images formed in this way are also discussed.     

四元裂解位相调制实现相干光通过散射介质聚焦

光在不均匀介质中传播会受到散射的干扰,在这些散射材料中,例如粉末、生物组织、亚波长颗粒对入射光多次散射使得出射光无法聚焦,从而在接收平面形成散斑.本文提出四元裂解位相调制方法对入射相干光场进行调制,使其通过散射介质聚焦.此方法利用入射光场全场调制,充分考虑光场单元之间的干涉作用,从整个空间光调制器的调制面开始,逐层进行四元裂解及位相优化.运用此方法在实验中实现了相干光的前向散射和后向散射有效聚焦,这为生物医学领域中通过散射介质成像提供了新的思路和方法.