Model-driven CT reconstruction algorithm for nano-resolution x-ray phase contrast imaging

The low-density imaging performance of a zone plate-based nano-resolution hard x-ray computed tomography(CT)system can be significantly improved by incorporating a grating-based Lau interferometer. Due to the diffraction, however,the acquired nano-resolution phase signal may suffer splitting problem, which impedes the direct reconstruction of phase contrast CT(nPCT) images. To overcome, a new model-driven nPCT image reconstruction algorithm is developed in this study. In it, the diffraction procedure is mathematically modeled into a matrix B, from which the projections without signal splitting can be generated invertedly. Furthermore, a penalized weighted least-square model with total variation(PWLSTV) is employed to denoise these projections, from which nPCT images with high accuracy are directly reconstructed.Numerical experiments demonstrate that this new algorithm is able to work with phase projections having any splitting distances. Moreover, results also reveal that nPCT images of higher signal-to-noise-ratio(SNR) could be reconstructed from projections having larger splitting distances. In summary, a novel model-driven nPCT image reconstruction algorithm with high accuracy and robustness is verified for the Lau interferometer-based hard x-ray nano-resolution phase contrast imaging.

Exact calculation of the minimal thickness of the large optical path difference wind imaging interferometer

This paper gives the relation between spatial ray and its projection on paper plane based on the vector form of reflective law. Using the method of prism expansion, it obtains the exact expression of the exit height. The exit height can ensure that the incident rays, at arbitrary direction and arbitrary angle, after several transmission and reflection in the two right-angle reflectors, finally pass through the exit surface. Furthermore, it analyses the effects of different parameters on the exit height through computer simulation, and some important conclusions are obtained. The physical meaning of the sign of exit height is described, and the exact expression of the minimal thickness of the large optical path difference wind imaging interferometer is gained. This work is of great scientific significance to the static, real- time simultaneous detection of atmospheric wind field, and it will provide a theoretical and practical guidance for the miniaturization design and engineering realization of wind imaging interferometer.

X-ray phase-sensitive microscope imaging with a grating interferometer:Theory and simulation

A general theoretical framework is presented to explain the formation of the phase signal in an x-ray microscope integrated with a grating interferometer,which simultaneously enables the high spatial resolution imaging and the improved image contrast.By using this theory,several key parameters of phase contrast imaging can be predicted,for instance,the fringe visibility and period,and the conversion condition from the differential phase imaging(DPI)to the phase difference imaging(PDI).Additionally,numerical simulations are performed with certain x-ray optical components and imaging geometry.Comparison with the available experimental measurement[Appl.Phys.Lett.113063105(2018)]demonstrates the accuracy of this developed quantitative analysis method of x-ray phase-sensitive microscope imaging.

Noncontact ultrasound sensing based on Mach-Zehnder homodyne interferometer for photoacoustic imaging

We present a novel noncontact ultrasound(US)and photoacoustic imaging(PAI)system,overcoming the limitations of traditional coupling media.Using a long coherent length laser,we employ a homodyne free-space Mach-Zehnder setup with zero-crossing triggering,achieving a noise equivalent pressure of 703 Pa at 5 MHz and a-6 dB bandwidth of 1 to8.54 MHz.We address the phase uncertainty inherent in the homodyne method.Scanning the noncontact US probe enables photoacoustic computed tomography(PACT).Phantom studies demonstrate imaging performance and system stability,underscoring the potential of our system for noncontact US sensing and PAI.

Experimental research on spectrum and imaging of continuous-wave terahertz radiation based on interferometry

A system for measuring terahertz spectrum is proposed based on optical interferometer theory, and is experimentally demonstrated by using a backward-wave oscillator as the terahertz source. A high-resolution, high-precision interferometer is constructed by using a pyroelectric detector and a chopper. The results show that the spectral resolution is better than 1 GHz and the relative error of frequency is less than 3%. The terahertz energy density distribution is calculated by an inverse Fourier transform and tested to verify the feasibility of the interferometric approach. Two kinds of carbon-fiber composites are imaged. The results confirm that the interferometer is useful for transmission imaging of materials with different thickness values.

Experimental research on the feature of an x-ray Talbot–Lau interferometer versus tube accelerating voltage

X-ray Talbot-Lau interferometer has been used most widely to perform x-ray phase-contrast imaging with a con- ventional low-brilliance x-ray source, and it yields high-sensitivity phase and dark-field images of samples producing low absorption contrast, thus beating tremendous potential for future clinical diagnosis. In this work, by changing the accel- erating voltage of the x-ray tube from 35 kV to 45 kV, x-ray phase-contrast imaging of a test sample is performed at each integer value of the accelerating voltage to investigate the characteristic of an x-ray Talbot-Lau interferometer （located in the Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Japan） versus tube voltage. Ex- perimental results and data analysis show that within a range this x-ray Talbot-Lau interferometer is not sensitive to the accelerating voltage of the tube with a constant fringe visibility of ~ 44%. This x-ray Talbot-Lau interferometer research demonstrates the feasibility of a new dual energy phase-contrast x-ray imaging strategy and the possibility to collect a refraction spectrum.

Present Status of EUV Interferometer Development at the Research Center for Soft X-ray Microscopy

A new interferometer for extreme ultraviolet (EUV) radiation with a laser produced plasma (LPP) laboratory source is under construction. The LPP source is operated with a Sn solid rod target on which pulsed YAG laser is focused to produce high temperature plasma emitting EUV radiation. The source is equipped with a newly designed debris stopper protecting a condenser multilayer mirror from the particle debris of the target. The condenser mirror focuses the light onto an EUV beam-splitter to form transmitted and reflected paths for producing interference fringes of a sharing type. The optical configuration is of a common path based on a triangular path type with a focusing at the beam-splitter, which is enabled to produce fringes by a low coherence radiation with a standard optical quality beam-splitter. The fringes are recorded by an imaging plate with pixels as small as 25μm. The dynamic range of linearity in detection of the EUV light was found to be more than 10 4 with sensitivity of 10 4 photons/pixel, enough for the purpose of interferogram recording, possibly with one laser shot.

Non-destructive study of fruits using grating-based X-ray imaging

Grating-based X-ray imaging can make use of conventional tube sources to provide absorption, refraction and scattering contrast images from a single set of projection images efficiently. In this paper, a fresh cherry tomato and a dried umeboshi are imaged by using X-ray Talbot–Lau interferometer. The seed distribution in the scattering image of the cherry tomato, and the wrinkles of epicarp in the refraction image of the umeboshi, are shown distinctly. The refraction and scattering images provide more information on subtle features than the absorption image. Also, the contrast-to-noise ratio values show distinguishing capacity of the three kinds of imaging techniques. The results confirm that grating-based X-ray imaging is of great potential in non-destructive fruit testing.

Shifting curves based on the detector integration effect for x-ray phase contrast imaging

In theory, we find that the actual function of the analyzer grating in the Talbot–Lau interferometer is segmenting the self-images of the phase grating and choosing integral areas, which make sure that each period of self-images in one detector pixel contributes the same signal to the detector. Furthermore, in the case of the lack of an analyzer grating, the shifting curves are still existent in theory as long as the number of fringes is non-integral in a detector pixel, which is a sufficient condition for creating shifting curve. The sufficient condition is available for not only the Talbot–Lau interferometer and the inverse geometry of Talbot–Lau interferometer, but also the x-ray phase contrast imaging system based on geometrical optics. In practical applications, we propose a method to improve the performances of the existing systems by employing the sufficient condition. This method can shorten the system length, is applicable to large period gratings, and can use the detectors with large pixels and large field of view. In addition, the experimental arrangement can be simplified due to the lack of an analyzer grating. In order to improve detection sensitivity and resolution, we also give an optimal fringe period.We believe that the theory and method proposed here is a step forward for x-ray phase contrast imaging.

嫦娥一号干涉成像光谱仪(IIM)2C级数据信息提取

通过分析Chang’E-1卫星所获取的高光谱数据的太阳高度角因素,选取了太阳高度角较高的IIM2C数据进行光谱定标。采用邻域平均法及邻域加权均值法对原始数据进行了杂点、条带修复。由于干涉成像光谱仪CCD阵列增益畸变以及它的自身问题使得干涉影像存在横向响应不均一性,提出采用基于子空间最大特征值法进行校正,结果影像亮度统计其强度表现均一,符合自然图像特征,并采用自编程序进行几何校正。运用国际上较为成熟的经验线性法对Chang’E-1IIM 2C数据进行绝对定标;与此同时,为了修正线性定标的偏置系数及降低数据噪声,首次采用自适应小波变换法对辐射定标后数据进行后处理,确定了IIM2C数据可用波段。通过对比国际标准定标点数据,制订了嫦娥IIM2C数据分析方案,完成了第一幅完整的Chang’E-1IIM 2C月球正面反射率影像。

双光源干涉法测量液态薄膜厚度

以迈克尔逊干涉仪为核心设备搭建实验系统,提出双光源光学干涉条纹的调试方案,引入基于Python的图像处理技术,分析基准图样与调节图样的重合度判断调节边界,实现薄膜厚度的精确测量。以肥皂膜为样品进行了实验,结果表明该实验方案具有良好的可操作性和可重复性,较目视估算法提升了测量精度,为无损测量液态薄膜厚度提供了解决方案,也可引入大学物理实验课程,提升学生研究创新能力。

基于白光干涉的三维表面形貌拼接方法研究

白光干涉测量技术由于具有非接触、无损伤、量程大、精度高和灵敏度高等特点,被应用于微纳米结构三维表面形貌测量中,但存在受限于显微物镜视场限制测量范围问题。提出了一种可以有效提高测量范围的三维表面形貌拼接方法。通过对多次采集的小范围高分辨率白光干涉图样进行域划分,采用三维形貌数据拼接配准方法,利用模板匹配算法对图像的二值化矩阵进行匹配计算,实现了待测元件的表面形貌的有效表征。研究发现,当采用不同的图像拼接方式即上下拼接、左右拼接和2&2拼接方式时,图像拼接效果有一定差异,其准确度和产生的误差不同。三种拼接方式中,2&2拼接方式能够有效减小操作误差,实现大范围和高分辨干涉图样拼接,在白光干涉三维形貌表征中具有广阔应用前景。

基于影像测量的三等标准金属线纹尺检定不确定度评定

以激光干涉仪为主标准器,结合显微镜瞄准和CCD影像采集装置检定三等金属线纹尺的实际长度,已成为目前常用的检定方法。文中从多个方面分析该方法检定三等金属线纹尺实际长度的测量不确定度来源,得到满足要求的评定结果。

Preliminary results of TiO_2 mapping using Imaging Interferometer data from Chang'E-1

The distribution of titanium abundance on the lunar surface is important knowledge for lunar geologic studies and future resource utilization.In this paper,we develop a preliminary model based on"ground truths"from Apollo and Luna sample-return sites to produce a titanium abundance map from Chang’E-1 Imaging Interferometer(IIM) images.The derived TiO2 abundances are validated with Clementine UVVIS results in several regions,including lunar highlands neighboring the Apollo 16 landing site,and high-Ti and low-Ti maria near the standard site of Mare Serenitatis(MS2) .The validation results show that TiO2 abundances modeled with Chang’E-1 IIM data are overestimated for highlands(～0.7 wt.%) and low-Ti maria(～1.5 wt.%) and underestimated for high-Ti maria(～0.8 wt.%).

Comparative analysis of phase extraction methods based on phase-stepping and shifting curve in grating interferometry

Two phase extraction methods which are based separately on phase-stepping and shifting curve are mainly used in phase-sensitive imaging in gating interferometry to determine the x-ray phase shift induced by an object in the beam. In this paper, the authors perform a full comparative analysis and present the main virtues and limitations of these two methods according to the theoretical analysis of the grating interferometry.

Preliminary results of FeO mapping using Imaging Interferometer data from Chang'E-1

Information about the variability,and spatial distribution of iron abundance is important to understand lunar geological history and for future resource utilization. In this paper we present a preliminary model to produce an iron abundance map using images taken by an Imaging Interferometer on board the satellite Chang'E-1. Compared with the Clementine UVVIS images,the images from the Chang'E-1 satellite also allowed for the extraction of FeO abundance distributions on the Moon. However,the prelimi-nary model results suggest an underestimation of ～2 wt.% for the FeO content of the mare region and an overestimation of ～3 wt.% for the highland region.

Quantitative coherence analysis of dual phase grating x-ray interferometry with source grating

Dual phase grating x-ray interferometry is compatible with common imaging detectors,and abandons the use of an absorption analyzer grating to reduce the radiation dose.When using x-ray tubes,an absorbing source grating must be introduced into the dual phase grating interferometer.In order to attain a high fringe visibility,in this work we conduct a quantitative coherence analysis of dual phase grating interferometry to find how the source grating affects the fringe visibility.Theoretical analysis shows that with the generalized Lau condition satisfied,the fringe visibility is influenced by the duty cycle of the source grating and the transmission through the grating bar.And the influence of the source grating profile on the fringe visibility is independent of the phase grating type.Numerical results illustrate that the maximum achievable fringe visibility decreases significantly with increasing transmission in the grating bar.Under a given transmission,one can always find an optimal duty cycle to maximize the fringe visibility.These results can be used as general guidelines for designing and optimizing dual phase grating x-ray interferometers for potential applications.

Lunar absolute reflectance as observed by Chang'E-1 Imaging Interferometer

Lunar absolute reflectance, which describes the fraction of solar radiation reflected by the Moon, is fundamental for the Chang'E-1 Imaging Interferometer(IIM) to map lunar mineralogical and elemental distributions. Recent observations made by the Spectral Irradiance Monitor(SIM) onboard the Solar Radiation and Climate Experiment(SORCE) spacecraft indicate that temporal variation in the solar radiation might have non-negligible influence on reflectance calculation, and the SIM measurements are different from the two previously used solar irradiances, i.e., ATLAS3 and Newkur. To provide reliable science results, we examined solar irradiance variability with the SIM daily observations, derived lunar absolute reflectances from the IIM 2A radiance with the SIM, ATLAS3 and Newkur data, and compared them with the Chandrayaan-1 Moon Mineralogy Mapper(M3), the Robotic Lunar Observatory(ROLO) and the Kaguya Multispectral Imager(MI) results. The temporal variability of the SIM solar irradiance is 0.25%–1.1% in the IIM spectral range, and less than 0.2% during the IIM observations. Nevertheless, the differences between the SIM measurements and the ATLAS3 and Newkur data can respectively rise up to 8% and 5% at particular IIM bands, resulting in discrepancy between which might affect compositional mapping. The IIM absolute reflectance we derived for the Moon using the SIM data, except for the last two bands, is consistent with the ROLO and the MI observations, although it is lower.

基于光栅干涉仪的暗场成像的Cramér-Rao下界

在光栅相衬成像中,通常使用相位步进法进行数据采集和信息提取。然而,对于相位步进法在提取暗场信号的算法效率还没有得到充分的评估。本研究引入Cramér-Rao下界对提取暗场信号的算法效率进行评估。基于理论分析和数值计算发现目前完全有效的算法仅适用于三步相位步进法,其他更多步数的相位步进法都是次优的。本研究以Cramér-Rao下界作为依据,定量地分析了相位步进数和可见度对算法效率的影响。结果表明在低可见度的情况下,相位步进法可以接近理论的最佳效率;在高可见度的情况下,当相位步进数大于5时,算法效率仅为77.4%,这可为基于X射线和中子光栅干涉仪的暗场成像的信噪比优化提高、剂量优化提供指导。

冲击波与爆轰实验瞬态光电测试技术研究进展

冲击波物理与爆轰物理是发展爆轰装置物理设计,工程设计和效应研究的重点基础学科,主要研究在爆炸、冲击和能量突然沉积等强动载荷下介质、材料与结构的力学响应、效应和工程技术应用。适用于极端环境的先进瞬态光电测试技术是冲击波物理与爆轰物理研究发展的重要推动力。根据国内外冲击波与爆轰实验瞬态光电测试技术发展现状,梳理归纳了以高速摄影、X射线闪光照相、瞬态全息成像、瞬态辐射测温、瞬态干涉测速测距等为主的瞬态光电测试技术的特点和典型技术指标,总结分析了相关技术的未来发展趋势,可为我国冲击波与爆轰实验瞬态光电测试技术发展提供一定参考。