混浊介质多光子激发显微成像的快速模型

将二维点扩散函数（PSF）和蒙特卡罗方法相结合,引入了一种研究混浊介质显微成像的快速仿真模型,将该模型用于混浊介质的多光子激发（MPE）显微成像研究,极大地提高了模拟效率,与直接蒙特卡罗方法计算结果的比较证实了该方法的正确性和有效性,此外,一个计算实例说明了混混介质的多光子激发显微成像具有比共焦荧光显微成像更优的横向分辨率。     

Wavefront Shaping for Fast Focusing Light through Scattering Media Based on Parallel Wavefront Optimization and Superpixel Method

When light travels in biological tissues,it undergoes multiple scattering and forms speckles,which seriousl.y restricts the penetration depth of optical imaging in biological tissues.With wavefront shaping method,by modulating the wavefront of incident light to compensate for the wavefront aberration,light focusing and scanning imaging through scattering media can be achieved.However,wavefront shaping must be accomplished within the speckle decorrelation time.Considering the short speckle decorrelation time of living tissues,the speed of wavefront shaping is rather essential We propose a new iterative optimization wavefront shaping method to improve the speed of wavefront shaping in which the existing parallel optimization wavefront shaping method is improved and is combined with the superpixel method.Compared with the traditional multi-frequency parallel optimization method,the modulation rate of our method is doubled.Moreover,we combine the high frame rate amplitude modulator,i.e.,the digital micromirror device(DMD),with the superpixel method to replace the traditional phase modulator(i.e.,spatial light modulator),which further increases the optimization speed.In our experiment,when the number of the optical modes is 400,light focusing is achieved with only 1000 DMD superpixel masks and the enhancement factor reaches 223.Our approach provides a new path for fast light focusing through wavefront shaping.     

Frequency bandwidth of light focused through turbid media

We study the effect of frequency detuning on light focused through turbid media. By shaping the wavefront of the incident beam light is focused through an opaque scattering layer. When detuning the laser we observe a gradual decrease of the focus intensity, while the position, size,and shape of the focus remain the same within experimental accuracy. The frequency dependence of the focus intensity follows a measured speckle correlation function. We support our experimental findings with calculations based on transport theory. Our results imply wavefront shaping methods can be generalized to allow focusing of optical pulses in turbid media.     

Active spectral filtering through turbid media

We demonstrate controlled wavelength-dependent light focusing through turbid media using wavefront shaping. Due to the dispersion caused by multiple light scattering, light propagation through turbid media can be independently controlled between different wavelengths. Foci with various wavelengths can be generated by applying different optimized wavefronts to a highly scattering layer. Given the linearity of the transmission matrix, multiple foci with different wavelengths can also be simultaneously constructed.     

混浊介质多光子激发荧光显微成像的蒙特卡罗模拟

将蒙特卡罗方法与几何光线追踪技术相结合用于研究样品混浊特性对多光子激发蒌光显微成像的影响。推导了模拟多层样品显微成像的数学模型,给出了用程序框图表示的基本仿真系统骨架,对传统蒙特卡罗方法的改进有效地增强了对聚焦光束的模拟能力,初步的模拟结果说明了混浊介质散射特性对显微成像的显著影响。     

Overcoming the diffraction limit using multiple light scattering in a highly disordered medium

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.     

Wide-field imaging through scattering media by scattered light fluorescence microscopy

To obtain images through scattering media, scattered light fluorescence (SLF) microscopy that utilizes the optical memory effect has been developed. However, the small field of view (FOV) of SLF microscopy limits its application. In this paper, we have introduced a re-modulation method to achieve wide-field imaging through scattering media by SLF microscopy. In the re-modulation method, to raster scan the focus across the object plane, the incident wavefront is re-modulated via a spatial light modulator (SLM) in the updated phase compensation calculated using the optimized iterative algorithm. Compared with the conventional optical memory effect method, the re-modulation method can greatly increase the FOV of a SLF microscope. With the phase compensation theoretically calculated, the process of updating the phase compensation of a high speed SLM is fast. The re-modulation method does not increase the imaging time. The re-modulation method is, therefore, expected to make SLF microscopy have much wider applications in biology, medicine and physiology.     

Pupil-segmentation-based adaptive optical microscopy with full-pupil illumination

Optical aberrations deteriorate the performance of microscopes. Adaptive optics can be used to improve imaging performance via wavefront shaping. Here, we demonstrate a pupil-segmentation based adaptive optical approach with full-pupil illumination. When implemented in a two-photon fluorescence microscope, it recovers diffraction-limited performance and improves imaging signal and resolution.     

Configuration optimization of laser guide stars and wavefront correctors for multi-conjugation adaptive optics

Multi-conjugation adaptive optics(MCAOs) have been investigated and used in the large aperture optical telescopes for high-resolution imaging with large field of view(FOV).The atmospheric tomographic phase reconstruction and projection of three-dimensional turbulence volume onto wavefront correctors,such as deformable mirrors(DMs) or liquid crystal wavefront correctors(LCWCs),is a very important step in the data processing of an MCAO's controller.In this paper,a method according to the wavefront reconstruction performance of MCAO is presented to evaluate the optimized configuration of multi laser guide stars(LGSs) and the reasonable conjugation heights of LCWCs.Analytical formulations are derived for the different configurations and are used to generate optimized parameters for MCAO.Several examples are given to demonstrate our LGSs configuration optimization method.Compared with traditional methods,our method has minimum wavefront tomographic error,which will be helpful to get higher imaging resolution at large FOV in MCAO.     

Effective point-spread function for fast image modeling and processing in microscopic imaging through turbid media

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.     

Elimination of beam walk-off in low-coherence off-axis photorefractive holography

Whole-field photorefractive holography can be combined with low-coherence interferometry for three-dimensional imaging and other applications, including imaging through turbid media, but the off-axis holographic recording geometry results in a limited field of view when light of low temporal coherence is used. We show that tilting the energy fronts with respect to the wave fronts by use of prisms can eliminate this problem and point out that this approach will be useful for many linear and nonlinear wave-mixing experiments.     

Estimation of optical abnormalities in breast phantom by diffuse equation

Optical imaging is an emerging method for bio-imaging. The advantages of this imaging provide non-ionizing and safe radiation, non-invasive and functional medical imaging. Due to diffusion of photons inside biological tissues, its image processing is complicated. So in spite of these advantages, this imaging method has not been progressed like ultrasound imaging and magnetic resonance imaging (MRI). Also, the penetration depth of photons inside biological phantom is low. To overcome this problem, the complicated diffusion of photons through tissue must be modeled. The diffuse equation can be applied to simulate photons through turbid media like biological tissues. In this paper, the diffuse equation is used to study propagation of diffuse photons. The green function method is applied to solve this equation, and then the optical properties of abnormalities in breast phantom are estimated. This fast method can be applied for image processing.     

Synthetic holography in microscopy: opportunities arising from advanced wavefront shaping

The advent of computer-generated or synthetic holography has created a wealth of possibilities for wavefront shaping in optics. We discuss the impact this has had on optical microscopy. Synthetic Holographic Microscopy utilises wavefront shaping by a computer-generated ‘hologram’ (CGH) to modify light on the illumination or the detection side, or both. This enables modifications of the general sample appearance concerning contrast, resolution and other aspects. Multiplexing CGHs can perform several tasks at once, for instance splitting the image into sub-images corresponding to different depths in the sample, or displaying differently contrasted images of the sample, e.g. bright field, darkfield or (spiral) phase contrast, in different sub-images. We give an overview of the options and discuss the advantages and disadvantages of using programmable holographic elements inside an optical microscope.     

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.     

宽场光学相干断层成像系统的三维显微成像

宽场相干断层成像技术（WFOCT）具有提高OCT系统的扫描速率和实现高分辨率的三维显微技术等优点,成为当前研究的热点。本文阐述了WFOCT的基本原理,利用八步移相法重建出玻璃物体微细结构的断层图像,研究了宽场OCT系统对玻璃材料的纵向分辨率和探测深度,其中探测深度可达3.3 mm。在获得多幅断层图像的基础上,利用VC6.0和OpenGL混合编程,采用移动立方体（MC）算法重建出玻璃物体微细结构的三维图像。实验结果表明,WFOCT系统不但能够在生物组织检测等医学方面得到应用,而且对反射率较高的物体能够完成三维形貌显微成像探测和深度探测。     

High-contrast imaging based on wavefront shaping to improve low signal-to-noise ratio photoacoustic signals using superpixel method

Photoacoustic(PA) imaging has drawn tremendous research interest for various applications in biomedicine and experienced exponential growth over the past decade. Since the scattering effect of biological tissue on ultrasound is two-to three-orders magnitude weaker than that of light, photoacoustic imaging can effectively improve the imaging depth.However, as the depth of imaging further increases, the incident light is seriously affected by scattering that the generated photoacoustic signal is very weak and the signal-to-noise ratio(SNR) is quite low. Low SNR signals can reduce imaging quality and even cause imaging failure. In this paper, we proposed a new wavefront shaping and imaging method of low SNR photoacoustic signal using digital micromirror device(DMD) based superpixel method. We combined the superpixel method with DMD to modulate the phase and amplitude of the incident light, and the genetic algorithm(GA) was used as the wavefront shaping algorithm. The enhancement of the photoacoustic signal reached 10.46. Then we performed scanning imaging by moving the absorber with the translation stage. A clear image with contrast of 8.57 was obtained while imaging with original photoacoustic signals could not be achieved. The proposed method opens new perspectives for imaging with weak photoacoustic signals.     

Comparison of frequency-domain and time-domain fluorescence lifetime tomography

We compare frequency-and time-domain formulations of deep-tissue fluorescence imaging of turbid media. Simulations are used to show that time-domain fluorescence tomography, implemented via the asymptotic lifetime-based approach, offers a significantly better separability of multiple lifetime targets than a frequency-domain approach. We also demonstrate experimentally, using complex-shaped phantoms, the advantages of the asymptotic time-domain approach over a Fourier-based approach for analyzing time-domain fluorescence data.     

Edge enhancement of phase objects through complex media by using transmission-matrix-based spiral phase contrast imaging

The wavefront shaping based technique has been introduced to detect the edges of amplitude objects through complex media, but the extraction of the boundary information of invisible phase objects through complex media has not been demonstrated yet. Here, we present a phase contrast imaging technique to overcome the scattering, aiming to achieve the edge detection of the phase object through the complex media. An operator based on the experimentally measured transmission matrix is obtained by numerically adding a spiral phase in the Fourier domain. With the inverse of the filtered transmission matrix, we can directly reconstruct the edge enhanced images for both amplitude object and phase object beyond scattering. Experimentally, both digital and real objects are imaged, and the results verify that isotropic edge detection can be achieved with our technique. Our work could benefit the detection of invisible phase objects through complex media.     

无透镜显微成像的重构算法研究

针对单幅图像进行了无透镜显微成像的重构算法研究，介绍了无透镜显微成像系统实验装置和ASM(angle spectrum method)、改编后的L-R(Lucy-Richardson)两种重构算法。对比两种算法重构后的USAF分辨率板图像的分辨率，利用瑞利判据得出ASM获得的振幅图分辨率最高(即3.10 μm)，且计算用时最少(即0.9 s)，证明了ASM为最佳的单幅无透镜显微重构算法。其次，利用无透镜显微成像系统结合ASM重构的方法，进行细胞成像实验。该无透镜成像视场为5×显微镜的4.4倍，且分辨率介于5×及10×光学显微镜之间，统计学优势明显，在生物医学领域具有广阔的应用前景。     

基于大数值孔径环形光锥照明的超分辨光学 显微成像方法研究

提出和发展了一种基于大数值孔径环形光锥照明的远场超分辨光学显微成像新方法, 采用将发光二极管(LED)面光源、窄带滤光和环形光锥照明相结合的特种照明方式, 实现超分辨显微成像. 建立了大数值孔径环形光锥照明成像的物理模型, 根据标量衍射理论, 在不同环形光锥照明时, 推导出光学显微系统像面衍射斑光强分布的理论计算公式; 通过Matlab求解和绘图, 得到衍射斑光强的分布图样, 从理论上证明这一成像方法可以有效提高光学显微镜的分辨率; 建立了相应的显微成像系统, 通过实验验证了该方法可有效改善显微镜的成像质量, 显著提高分辨率; 在中心波长450 nm、环形光锥数值孔径1.125—1.25时, 实验获得的分辨率至少优于150 nm, 与理论研究结果相符合, 从而证明了这一方法的可行性.