Tomographic Imaging of Collagen Fiber Orientation in Human Tissue Using Depth-Resolved Polarimetry of Second-Harmonic-Generation Light

We propose a nonlinear optical probe method to image the distribution of collagen fiber orientation in human tissue by measuring the polarization of collagen-induced second-harmonic-generation (SHG) light (SHG polarimetry). Depth-resolved SHG polarimetry, with a depth resolution of 14 μm, was used to evaluate the cross-sectional profile of collagen fiber orientation in Achilles tendon and dentin, revealing a characteristic distribution of collagen orientation along the depth direction. We evaluated the two-dimensional (2D) lateral distribution of collagen fiber orientation in back reticular dermis and anklebone by polarization-resolved SHG imaging, and confirmed an appreciable difference in the distribution profiles of the two samples. We further extended the method to a depth-resolved measurement of the three-dimensional (3D) distribution of collagen orientation in anklebone. The proposed system promises to be a powerful tool for in vivo measurement of collagen fiber orientation in human tissue.     

Macromolecular structure of cellulose studied by second-harmonic generation imaging microscopy

The macromolecular structure of purified cellulose samples is studied by second-harmonic generation (SHG) imaging microscopy. We show that the SHG contrast in both Valonia and Acetobacter cellulose strongly resembles that of collagen from animal tissues, both in terms of morphology and polarization anisotropy. Polarization analysis shows that microfibrils in each lamella are highly aligned and ordered and change directions by 90 degrees in adjacent lamellae. The angular dependence of the SHG intensity fits well to a cos2 theta distribution, which is characteristic of the electric dipole interaction. Enzymatic degradation of Valonia fibers by cellulase is followed in real time by SHG imaging and results in exponential decay kinetics, showing that SHG imaging microscopy is ideal for monitoring dynamics in biological systems.     

A quasi-crystal model of collagen microstructure based on SHG microscopy

<正>Second harmonic generation(SHG) results from molecules which are polarized by an external electric field often provided by an intense laser beam.The polarizability depends on firstly the intrinsic structural properties of the substance and hence the second-order nonlinear susceptibility,and secondly the intensity and polarization direction of the incident light.The polarization characteristics of the beam are therefore of interest.In this letter,we discuss some considerations in SHG microscopy of collagen when the incoming beam is circularly polarized,and present some supporting results as well as a numerical analysis.We propose a quasi-crystal model of collagen microstructure in an effort to further our understanding on this protein.     

The temperature dependence of surface second-harmonic generation from the air-water interface

An investigation of the polarization and temperature dependence of surface second-harmonic generation (SHG) at the air-water interface shows that the intensity of the SHG signal decreases over the range 20–70°C. Accounting for the changes in the SHG polarization behaviour with temperature to extract the relative temperature dependence of X_zzz shows that it is similar to that obtained from simulation studies. The role of the interfacial refractive index in the interpretation of the SHG signals is addressed.     

Second harmonic generation from thick leaves using the two-photon laser scanning microscope

A laser-scanning microscope using second harmonic generation (SHG) as a probe is shown to produce high-resolution images of duckweed Lemna minuta leaves. These leaves are multi-cell layer thick. Second harmonic light is generated by a tightly focused short pulse laser beam and is collected by two objectives yielding forward and backward second harmonic digital images. This measurement shows that the signal of the second harmonic imaging in the forward and backward directions depends on the thickness of the chloroplast and that the forward-SH image was brighter than the backward-SH image. The image intensity also depended on the orientation of the chloroplast in relation to the illuminating polarization direction. Their light-induced re-orientation which was affected by the intensity of the illumination could be observed during the experiments.The novelty of this work is to establish new compact technique in which one can use the SH imaging to investigate the true architecture of the sensitive samples, the unknown samples and the samples which is not producing auto-fluorescence. Moreover, investigation of new or unknown samples needs a long time for looking at details of the sample. Thereby the sample will be exposed for long time to the laser radiation that will cause photobleaching and photodamage. Since the SHG does not undergo photobleaching and photodamage this will be the promising technique for investigating the sensitive and new unknown samples. Then one can move to acquire fluorescence images after complete investigation of the true architecture of the sample. The other advantage of SHG is that it has the ability to image highly ordered structural proteins without any exogenous labels. The SHG is an intrinsic and a coherent process. Imaging of intrinsic compounds avoids the complications of slicing and labeling, and samples can be investigated under physiological conditions.     

手性薄膜表面二次谐波圆二向色性的研究

给出了螺旋型手性分子薄膜表面反射方向的圆二向色性的谐波强度表示式,分析了谐波的强度与手性分子的取向,分子的螺距和半径等结构参数的关系,给出了数值模拟结果,发现在入射光强一定的情况下,谐波强度在螺距和半径的取值范围内分别存在着最大值,以及螺距与半径之间满足的关系式随分子取向角的变化而不同。     

Surface plasmon effects on surface second harmonic generation during Au nanoparticle deposition onto H–Si(1 1 1)

Deposition of Au nanoparticles from aqueous HF onto H–Si(1 1 1) was studied in situ by surface second harmonic generation (SHG) and ex situ by extinction spectroscopy and non-contact atomic force microscopy (AFM). AFM measurements indicate that the maximum SHG intensities occur at lateral particle diameters of approximately 90–100 nm independent of solution phase composition, but with an intensity that depends on solution phase composition.

Employing the evolution of SHG intensity to monitor lateral cluster growth, simultaneous Au deposition and Si oxidation exhibit apparent kinetic reaction orders of 1/2 and zero with respect to HF and Au(CN)₂⁻, respectively. These results are similar to those obtained purely from ex situ AFM analysis. The variations in SHG intensity with Au(CN)₂⁻ concentration can be related to particle nucleation densities. These results demonstrate the utility of SHG as an in situ probe of particle growth.     

超高真空中C60光聚合效应光学二次谐波的研究

利用１．０６４μｍ基频超短脉冲激光，使用光学二次谐波方法研究了超高真空中蒸镀在多晶银表面上的Ｃ６０薄膜紫外光照射下的光聚合现象，发现聚合以后的Ｃ６０二阶非线性响应增强，同时观察到光聚合的饱和效应，Ｃ６０光聚合二阶非线性的提高可以用电四极了磁偶极子对二次谐波贡献的增强来解释。     

Nondestructive evaluation of incipient corrosion in a metal beneath paint by second-harmonic tomography

A second-harmonic optical scanning imaging method for nondestructive evaluation of corrosion of painted metals is demonstrated. Two-dimensional images of the sectional structure from a sample of painted metal with corrosion were obtained by detection of second-harmonic generation (SHG). The second-harmonic signals generated from paint, corrosion, and metal can be spatially imaged in ~10-mum sliced subsurface layers. Corroded metal layers covered with paint are found to have more intensity variation than normal polished metal. The spatial mapping of the second-harmonic signals shows depth differentiation of paint, corrosion, and metal surfaces. The depth of corrosion beneath the paint can be measured from the SHG images.     

RELATIONSHIP BETWEEN INTENSITY OF SURFACE SECOND HARMONIC GENERATION ANDMOLECULAR STRUCTURE INHELIX MOLECULAR FILMS

The relationship between intensity of surface Second Harmonic Generation (SHG) and the pitch, radius and azimuthal angle of molecules on the surface of helix molecular films is analyzed. The values of pitch and radius corresponding to the maximal intensity of SHG have been shown to exist. The theoretical results are compared with the experimental ones reported by Mohlman et al., and the limitation of their conclusion is also pointed out.     

RELATIONSHIP BETWEEN INTENSITY OF SURFACE SECOND HARMONIC GENERATION AND MOLECULAR STRUCTURE IN HELIX MOLECULAR FILMS

The relationship between intensity of surface Second Harmonic Generation (SHG) and the pitch, radius and azimuthal angle of molecules on the surface of helix molecular films is analyzed. The values of pitch and radius corresponding to the maximal intensity of SHG have been shown to exist. The theoretical results are compared with the experimental ones reported by M?hlman et al., and the limitation of their conclusion is also pointed out.     

Influence of the sample-probe coupling on the resolution of transmitted near-field optical image

Numerical simulation of photon scanning tunneling microscopy is presented to study the near-field distribution in the vicinity a dielectric surface with one-dimensional sub-wavelength structures. Multiple scattering between the probe tip and the sample has been taken into account implicitly by matching electromagnetic boundary conditions at interfaces. The near-field intensity in transmission mode through two ridges on surface has been modeled in order to analyze the resolution of the system. The effects on the signal by the sample-tip coupling, the polarization of the incident light, and the angle of incidence are investigated. We find that the capability to recognize the feature will be improved when the tip–object interaction is strong.     

Study on effective probe depth of optical coherence tomography system by Monte Carlo simulation

The intensities of Class I and Class II signals at several different probing depths and different coherence lengths are analyzed using a Monte Carlo model with a pencil beam, and the result shows that the longitudinal resolution has influence on the effective probe depth. A Monte Carlo model for optical coherence tomography system with a focused Gaussian beam is proposed. The intensities of Class I and Class II signals at different probing depth for different radius and depth of focus of the beam are simulated using this model. We found that increasing of the depth of focus and decreasing of the beam radius can finitely increase effective probing depth. When the effective probing depth is fixed, optimal signal intensity can be achieved by altering the beam radius or the depth of focus.     

Tightly focusing of linearly polarized vortex beams through a dielectric interface

Based on vectorial Debye theory, the tightly focusing properties of linearly polarized vortex beams through a dielectric interface are studied. Then the intensity distribution in the focal region is investigated in detail by numerical calculations. The focal shifts induced by the mismatch of the refractive indices across the interface has been found. And the dependence of focal shifts and spot size of the focused field on the probe depth and numerical aperture of the objective are presented. Furthermore, the characteristic of intensity pattern of the cross section of the focused field is illustrated, finding that the intensity pattern rotates with the propagation of beams.     

Nonlinear optical and electrostatic force microscopy for ferroelectric polarization imaging

Second-harmonic generation (SHG)-based nonlinear optical microscopy is used for spatially resolved imaging of the polarization switching in lead zirconium titanate ferroelectric thin films. The local SHG hysteresis loops reveal a strong dependence on film composition and structure. The SHG microscopy results are in good agreement with the efficiency of electrostatic force microscopy writing and allow us to predict the microscopic dielectric memory efficiency, both in contact and contact-less ways. Received: 15 January 2001 / Revised version: 27 March 2002 / Published online: 6 June 2002     

Second harmonic generation in planar chiral nanostructures

The effect of the chirality of planar spiral nanostructures on optical second harmonic generation (SHG) is studied in the paper. It is shown that the intensity of left and right circularly polarized SHG differs for structures of different handedness and the direction of the SHG polarization rotation plane is opposite for enantiomers.     

有机/无机薄膜凝胶动态过程的实时光学二次谐波产生研究

采用实时光学二次谐波产生(SHG)测量方法,以两亲性分子半花菁为掺杂探针分子,对溶胶-凝胶技术制备的玻璃薄膜的凝胶干燥的动态过程进行了研究.结合紫外—可见吸收光谱的测量,发现：因两亲性分子在膜中的自取向性可诱导出二阶光学非线性,溶胶-凝胶技术制备的有机/无机复合膜的凝胶干燥过程可通过薄膜SHG强度的变化半定量地反映.凝胶干燥收缩导致有序掺杂分子数减少,膜片的光学非线性减弱.该过程随薄膜处理温度的升高而急剧缩短;另外,有机分子在膜中的聚集程度随膜片处理温度的增加而很快减少. 关键词：     

三维光存储中折射率失配引起的球差补偿

为实现三维光存储中折射率失配引起的球差补偿,建立了光学存储系统模型,获得了折射率失配引起的波前偏差函数与存储深度的表达式.采用泽尔尼克循环多项式对波前偏差函数进行补偿展开.在双光子荧光和单光子共焦荧光读出方式下,均可获得读出荧光强度与存储深度的关系:在折射率失配引起的球差未得到补偿矫正的情况下,存储深度在200 μm左右读出荧光强度基本上下降为零;当折射率失配引起的初级球差被补偿矫正后,读出荧光强度随存储深度的下降得到较好改善;当折射率失配引起的二级球差被补偿矫正后,存储深度在1 mm内存储点强度随深度基本上没有明显地变化.并且对像差补偿方法进行了具体地分析.     

31P NMR表面线圈探头射频场B1的空间分布特性研究

对本实验室自制的³¹P表面线圈探头的射频场B₁强度的空间分布和脉冲宽度进行了初步研究.结果表明该表面线圈中心的90°脉冲约为10μs.得到的信号主要是线圈圆周内射频场B₁作用的结果,在垂直线圈平面的方向上随距离增加,信号迅速减弱.因此该表面线圈射频场B₁有效的作用范围在一个近半圆球体内,底面积半径约为线圈外半径,有效作用深度约为线圈半径.     

数值分析在不同偏振时复杂样品的近场强度分布

采用三维时域有限差分法(FDTD),模拟计算了光子扫描隧道显微镜(PSTM)系统中的介质和银质金属样品在不同偏振模式光源下的近场强度分布。使用介质小样品检验探针性能,在探针不同位置计算得到了相似的近场强度分布图,说明编写的程序是可信的。给出了等高扫描时p偏振和s偏振条件下,“PSTM”字样介质样品和银质金属样品上方5nm处的近场强度分布图,结果显示:对介质样品,p偏振波能较好的反映样品的形貌,这是由入射电场的方向决定的;银质金属有表面增强作用,对不同偏振波均能在某种程度上反映样品的形貌,仍有待近一步的研究。