Laser-induced pattern formation in liquid sulfur

Liquid sulfur is a well-known liquid which exhibits a polymerization transition at T_p=159 °C. Recently, it was found from our experiments that such a transition can be induced below T_p through laser illumination and that an iridescent pattern appears under strong illumination with a pulsed laser of more than 60 mJ/cm² pulse. It is proposed that the visible change in iridescence is due to a macroscopic reconstruction of laser-generated polymers and that a laser-induced phase transition takes place from a freely expanded polymer phase to an ordered polymer phase when increasing the laser illumination. To further examine this possibility, the time variation of the iridescent pattern has been fully investigated using a macro lens, a polarized microscope and an optical microscope. In an analysis of the iridescent pattern, a rapid decrease in the area was observed after an initial slow decrease, suggesting a type of phase transition. Results from the observation of a quenched sulfur sample with a polarized microscope gave evidence that the iridescent region consists of polymers. Through observation of the liquid with a microscope, a striped pattern with micrometer sized spacing was noted in the iridescent pattern. A drastic color change was observed in the pattern from its generation to its disappearance. Sample thickness dependence of the pattern was also observed. These results were well explained by assuming the self-arrangement of laser-generated colloidal polymers.     

Nanofabrication and characterization of a grating‐based condenser for uniform illumination with hard X‐rays

In the development of full‐field transmission X‐ray microscopy for basic study in science and technology, a condenser capable of providing intense illumination with high uniformity and stability on tested specimens in order to achieve high‐quality images is essential. The latest design of a square‐shaped condenser based on diffractive gratings has demonstrated promising uniformity in illumination. This paper describes in more detail the development of such a beam shaper for hard X‐rays at 10 keV with regard to its design, manufacture and optical characterization. The effect of the grating profile on the diffracted intensity has been theoretically predicted by numerical simulation using the finite‐difference time‐domain method. Based on this, the limitations of the grating‐based condenser are discussed.     

All-incoherent dispersion-compensated optical correlator

We report on a simple, spatially incoherent, wavelength-independent imaging system that, in contrast to the conventional case, exhibits a dispersion-compensated point-spread function. Our hybrid (diffractive-refractive) three-lens imaging configuration thus acts as an all-incoherent dispersion-compensated optical irradiance correlator. So the optical arrangement is well adapted to processing color information (both spatially and temporally incoherent) under natural illumination.     

Spectral contrast imaging microscopy

We introduce a new technique, spectral contrast imaging microscopy (SCIM), for super-resolution microscopic imaging. Based on a novel contrast mechanism that encodes each local spatial frequency with a corresponding optical wavelength, SCIM provides a real-time high-resolution spectral contrast microscopic image with superior contrast. We show that two microscopic objects, separated by a distance smaller than the diffraction limit of the optical system, can be spatially resolved in the SCIM image as different colors. Results with numerical simulation and experiments using a high-resolution United States Air Force target are presented. The ability of SCIM for imaging biological cells is also demonstrated.     

Application of a femtosecond self-sustaining mode-locked Ti:sapphire laser to the field of laser scanning confocal microscopy

Developments in ultrafast Ti:sapphire laser technology can be applied in the investigation of nonlinear optical processes. We describe the application of a self-sustaining femtosecond Ti:sapphire laser as an illumination source in the field of confocal laser scanning fluorescence microscopy (LSM). We present spectra for various fluorescent stains under two-photon excitation and present LSM images of stained samples under mode-locked illumination. The potential for such a system as a non-destructive technique for studying live cells in biomedical research is discussed.     

Resolution of 90 nm (lambda/5) in an optical transmission microscope with an annular condenser

Resolution of 90 nm was achieved with a research microscope simply by replacing the standard bright-field condenser with a homebuilt illumination system with a cardioid annular condenser. Diffraction gratings with 100 nm width lines as well as less than 100 nm size features of different-shaped objects were clearly visible on a calibrated microscope test slide. The resolution increase results from a known narrower diffraction pattern in coherent illumination for the annular aperture compared with the circular aperture. This explanation is supported by an excellent accord of calculated and measured diffraction patterns for a 50 nm radius disk.     

Wide-field high-resolution structured illumination solid immersion fluorescence microscopy

The use of aplanatic solid immersion lenses (ASILs) made of high-refractive-index optical materials provides a route to wide-field high-resolution optical microscopy. Structured illumination microscopy (SIM) can double the spatial bandwidth of a microscope to also achieve high-resolution imaging. We investigate the combination of ASILs and SIM in fluorescence microscopy, which we call structured illumination solid immersion fluorescence microscopy (SISIM), to pursue a microscopic system with very large NA and high lateral resolution. We demonstrate that the combination can produce a wide-field high-resolution microscopic system with bandwidth corresponding to an NA of 3. Future developments of the SISIM system to make it achieve even higher resolution are proposed.     

Compositional contrast of uncoated fungal spores and stained section-face by low-loss backscattered electron imaging

Comparative surface imaging was performed on uncoated fungal spores and stained section-face by field emission scanning electron microscopy with an in-column energy-selective backscattered electron detector. Epoxy resin thin sections (ca. 200 and 500 nm thick) of the osmicated and uranyl acetate/lead citrate-stained fungus were examined with the microscope. Topographical contrast was evident in secondary electron imaging by either a below-lens or an in-lens detector. Meanwhile, low-loss backscattered electron images showed mainly compositional contrast at low accelerating voltages (mostly below 1 kV). With attenuated topographical contrast, several different electron densities could be detected, exhibiting several levels of electron density even on a flat plane of spines. Minute differences in topography on epoxy resin sections as seen by secondary electron imaging represented the periphery of the fungal spores and hyphae. On the other hand, the compositional contrast could be retrieved from stained section-face in low-loss BSE imaging, revealing subcellular entities after contrast inversion. The resolution of low-loss BSE imaging was sufficient to resolve plasma membrane, and various types of vacuoles and vesicles. These results suggest that low-loss backscattered electron imaging could potentially provide compositional information to resolve surface chemical features of uncoated microbial cells and stained section-face with heterogeneous surface compositions.     

Wave field restoration using focal-depth extension techniques under dynamic hollow-cone illumination

Wave field restoration has been achieved based on focal-depth extension under dynamic hollow-cone illumination using an optical microscope. Two kinds of focal-depth extension techniques, such as moving focus averaging and an objective annular aperture, were compared and their effectiveness for transmission electron microscopy applications is discussed. Both techniques enabled resolution enhancement at the same level and effectively obtained aberration-free phase and amplitude images separately by canceling out the rotationally invariant component of system wave aberrations, such as spherical aberration. The influence of nonlinear interference on image contrast was confirmed as significant by using a figure 8 shaped spatial frequency filter.     

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.     

Condenser for Koehler-like illumination in transmission x-ray microscopes at undulator sources

We report on a novel condenser for full-field transmission x-ray microscopes that use synchrotron radiation from an undulator source. The condenser produces a Koehler-like homogeneous intensity distribution in the sample plane and eliminates object illumination problems connected with the high degree of spatial coherence in an undulator beam. The optic consists of a large number of small linear diffraction gratings and is therefore relatively easy to manufacture. First imaging experiments with a prototype condenser were successfully performed with the Twinmic x-ray microscope at the Elettra synchrotron facility in Italy.     

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。     

深海光学照明与成像系统分析及进展

深海光学成像系统分为4个子系统:照明系统、相机系统、图像处理系统以及数据存储与传输系统,本文对深海光学成像系统化研究与发展趋势展开分析。文中有针对性地对深海光学成像最前端的两个子系统-照明系统与相机系统进行了较为详细地阐述。其中,深海照明系统进一步细分为3个更小的系统:光源系统、配光系统以及灯阵系统;对于深海相机系统则根据其应用领域及技术特点细分为水下普通成像、激光成像、偏振光成像、3D/全景成像、显微成像以及光谱成像6类。从近年来国内外深海光学成像的发展历史及现状来看,其未来的发展趋势可以归结为以下几点:更高的分辨率,更深的工作深度,更大的观测范围以及更多样的成像方式。     

Quantitative phase microscopy of biological samples using a portable interferometer

This Letter presents the τ interferometer, a portable and inexpensive device for obtaining spatial interferograms of microscopic biological samples without the strict stability and the highly coherent illumination that are usually required for interferometric microscopy setups. The device is built using off-the-shelf optical elements and can easily operate with low-coherence illumination, while being positioned in the output of a conventional inverted microscope. The interferograms are processed into the quantitative amplitude and phase profiles of the sample. Based on the phase profile, the optical-path-delay profile is obtained with temporal stability of 0.18 nm and spatial stability of 0.42 nm. Further experimental demonstration of using the τ interferometer for imaging the quantitative thickness profile of a live red blood cell is provided.     

基于微球透镜的任选区高分辨光学显微成像新方法研究

提出和发展了基于毛细管-微球组合探针的任选区、 高分辨显微成像新方法. 建立了微球显微成像的物理模型, 利用成像理论,推导出微球成像的放大倍率; 采用3.0, 4.4, 5.6, 7.5, 10.0 μm等不同直径的SiO₂微球, 对未经刻录的DVD光盘进行了微球显微成像实验, 可以观察到DVD光盘的微纳米结构被明显放大且对比度显著提高, 与理论计算结果相符合; 采用毛细管微探针操纵微球的方法, 实现了基于微球透镜阵列的样品微纳米结构的高分辨显微成像; 在此基础上, 进一步将毛细管微探针与微球组合, 制备出毛细管-微球组合型探针, 首次实现了基于微球透镜的样品任意区域高分辨显微成像.     

Beam‐shaping condenser lenses for full‐field transmission X‐ray microscopy

A new type of diffractive X‐ray optical elements is reported, which have been used as beam‐shaping condenser lenses in full‐field transmission X‐ray microscopes. These devices produce a square‐shaped flat‐top illumination on the sample matched to the field of view. The size of the illumination can easily be designed depending on the geometry and requirements of the specific experimental station. Gold and silicon beam‐shapers have been fabricated and tested in full‐field microscopes in the hard and soft X‐ray regimes, respectively.     

Programmable aperture microscopy: A computational method for multi-modal phase contrast and light field imaging

We demonstrate a simple and cost-effective programmable aperture microscope to realize multi-modal computational imaging by integrating a programmable liquid crystal display (LCD) into a conventional wide-field microscope. The LCD selectively modulates the light distribution at the rear aperture of the microscope objective, allowing numerous imaging modalities, such as bright field, dark field, differential phase contrast, quantitative phase imaging, multi-perspective imaging, and full resolution light field imaging to be achieved and switched rapidly in the same setup, without requiring specialized hardwares and any moving parts. We experimentally demonstrate the success of our method by imaging unstained cheek cells, profiling microlens array, and changing perspective views of thick biological specimens. The post-exposure refocusing of a butterfly mouthpart and RFP-labeled dicot stem cross-section is also presented to demonstrate the full resolution light field imaging capability of our system for both translucent and fluorescent specimens.     

Three-dimensional modeling of amplitude-object imaging in scanning near-field optical microscopy

The imaging properties of the transmission-illumination mode of a scanning near-field optical microscope are investigated. Three-dimensional calculations of the power transmitted into classically allowed and forbidden regions for a nonsymmetrically positioned amplitude object are implemented by use of the finite-difference time-domain solution of Maxwell's equations. The evolution of the images with the distance from the object as well as the effect of the polarization of the illumination is shown. The computations show that for applications involving the imaging of an amplitude object, the use of the allowed light is preferred. Collection of light from both the allowed and the forbidden zones leads to degraded contrast and resolution.     

模拟退火算法色差校正的傅里叶叠层显微彩色成像技术

提出一种基于模拟退火算法的自动聚焦方法,可以分别重建三种照明色光的高分辨率图像,从而实现高分辨率彩色图像的构建.模拟仿真和分辨率靶及生物切片样品实验结果均表明,即使色差较严重的显微系统,利用该方法也能准确地获得高分辨率彩色图像,极大降低了对显微镜的性能要求,扩展了傅里叶叠层彩色成像的适用范围.     

Simultaneous optically sectioned fluorescence and optical coherence microscopy with full-field illumination

Full-field optical coherence microscopy (FF-OCM) and optically sectioned fluorescence microscopy are two imaging techniques that are implemented here in a novel dual modality instrument. The two imaging modalities use a broad field illumination to acquire the entire field of view without raster scanning. Optical sectioning is achieved in both imaging modalities owing to the coherence gating property of light for FF-OCM, and a structured illumination setup for fluorescence microscopy. Complementary image data are provided by the dual modality instrument in the context of biological tissue screening. FF-OCM imaging modality shows the tissue microarchitecture, while fluorescence microscopy highlights specific tissue features with cellular-level resolution by using targeting contrast agents. Complementary tissue morphology and biochemical features could potentially improve the understanding of cellular functions and disease diagnosis.