太赫兹时域光谱仪在陶瓷涂层及低压气体检测中的应用

太赫兹时域光谱仪(Terahertz Time-Domain Spectrometer, THz-TDS)在光谱学、材料表征、安检、通信等众多领域具有广阔的应用前景。首先介绍了一种稳定的1560 nm光纤短脉冲激光器及其用于THz-TDS系统的集成。然后用该THz-TDS系统对几种陶瓷基复合材料(Ceramic Matrix Composites, CMC)进行了无损检测。特别是在对热障涂层的厚度进行检测时,实现了微米量级的检测精度。与传统方法相比,太赫兹波对CMC具有较强的穿透性并且应用灵活,因此可提供更好的解决方案。最后,采用太赫兹异步光学采样(Terahertz ASynchronous OPtical Sampling, THz-ASOPS)系统对低压水蒸气进行了高分辨率光谱分析。结果表明,该系统的光谱分辨率达到10 MHz,比传统的THz-TDS提高了100倍以上。     

正弦相位调制全深度频域多普勒光学相干层析成像技术

将多普勒探测与正弦相位调制复频域光学相干层析成像技术(OCT)相结合,建立了基于正弦相位调制的全深度频域多普勒光学相干层析成像系统。利用正弦相位调制B-M扫描方法,并采用傅里叶变换结合带通滤波的方法重建复干涉谱信号,获得全深度层析及多普勒图像。成像深度范围扩大为原来的2倍,在整幅图像范围内均可获得较高的速度探测灵敏度。基于该系统获得了血流仿体的全深度层析图及全深度多普勒图。实验测量的系统最小可探测速度为5.35μm/s。     

非视域快速成像系统研究初探

非视域(Non-Line-of-Sight, NLOS)成像技术可以对被其他物体遮挡住(如拐角处、烟雾后等)的隐藏目标进行探测和成像,因此在机器视觉、安防、医学影像、灾难救援和自动驾驶等领域具有重要的应用价值。该技术通过利用脉冲激光束和时域信号探测器扫描特定表面来实现上述功能。目前NLOS技术仍然存在诸多不足之处,比如扫描时间长、计算时间长等。针对这些情况,提出了一种凝视型快速探测与重建方法。模拟结果表明,该方法可探测高反射物体,并可有效增大视域范围。     

武汉电离层斜向探测系统的时间同步设计

为武汉电离层斜向探测系统设计了一种新的时间同步方式.该同步方式利用全球定位系统(GPS)接收机输出的时钟信号校正高性能恒温晶振输出的参考时钟信号,从而获得稳定可靠的秒脉冲信号来用作斜测系统的时间同步信号.在预定的探测时刻,单片机利用该信号控制斜测系统的发射端和接收端同时开始工作,从而实现时间同步.实验结果表明:该时间同步方式在获得GPS卫星信号的情况下,时间同步精度可达到30ns.而在未获得GPS卫星信号的24小时内,时间同步精度可达到1μs.在获得和一定时间内未获得GPS卫星信号的情况下,采用该时间同步方式的武汉电离层斜向探测系统都成功地获得了斜向探测电离图,从而很好地满足了探测需求.     

投影装置中的激光扫描自动对准

众所周知,采用激光扫描方法进行自动对准,对于接触式和接近式都是一种有利的技术,并且该方法现已用于实际中了。该方法采用激光光点作为探针同时探测来自掩模和硅片的信息。激光光束在物体上形成一很小的光点,并且通过旋转的多梭反射镜和F—θ光学系统对物体进行恒速扫描。物体上的对准标记沿着扫描线设置。为了增大物体信息信号—噪声的比率系数,可用光学滤波方法对标记的部份散射光进行有选择的探测,采用此方法可获得硅片信息的高效率探测,以及高精度的自动探测。该激光光点扫描方法也可同样方便的用于投影复印技术中,如透镜或反射镜系统中。在充分利于投影装置的特性方面,该方法又具其独特的优点。例如,通过混合使用一个四分之一波片或相移反射镜以及利用激光器的偏振特性,便可消除掩模与硅片之间盼干涉现象,因而可获得稳定的输出信号,并可使对准精度达到0.3微米(2σ)。     

飞秒激光成丝过程中的太赫兹波超光速传输现象研究

通过使用太赫兹(Terahertz,THz)时域光谱系统,探测从不同长度飞秒激光光丝辐射出的THz脉冲,观察到THz波在飞秒激光成丝过程中超光速传输的实验现象。进一步的分析表明:THz波在等离子体光丝区域的折射率小于其在空气中的折射率,这是使得THz波能够在成丝过程中超光速传输的主要原因。由此可以推测:THz脉冲极有可能是在等离子体光丝中进行导引传输的。最后,通过数值模拟获得了光丝区域内的THz本征模式,从而验证了上述推测。     

太赫兹时域光谱仪在陶瓷涂层及低压气体检测中的应用

太赫兹时域光谱仪(Terahertz Time-Domain Spectrometer,THz--TDS)在光谱学、材料表征、安检、通信等众多领域具有广阔的应用前景。介绍了一种稳定的波长为1560 nm的光纤短脉冲激光器以及一种基于该激光器的THz--TDS系统。然后用该系统对几种陶瓷基复合材料(Ceramic Matrix Composites,CMC)进行了无损检测。特别是在对热障涂层(Thermal Barrier Coating,TBC)的厚度进行检测时,实现了微米量级的精度。相比于传统方法,太赫兹波对CMC具有较强的穿透性并且应用灵活,因此提供了更好的解决方案。最后使用太赫兹异步光学采样系统(Terahertz Asynchronous Optical Sampling,THz--ASOPS)对低压水蒸气进行了高分辨率光谱分析。结果表明,光谱分辨率达到10 MHz,比传统的THz--TDS提高了100倍以上。     

基于亮温光谱的表面沾染物探测方法

针对表面沾染探测中存在的不足,提出亮温光谱法。通过高灵敏度红外遥测光谱仪非接触探测获得沾染物的辐亮度光谱,利用光源和沾染本底的高发射率特性,通过普朗克公式转换得到亮温光谱,直接获得沾染物特征信息。无需预测沾染本底,特别适合已中毒事故现场。首先讨论该方法的探测原理,然后分别使用亮温光谱法和背景扣除法对铝板表面的沾染物二甲基硅油(Poly(dimethylsiloxane),PDMS)和磷酸三乙酯(Triethyl phosphate,TEP)进行探测。结果表明,亮温光谱法提取出的沾染物的特征与背景扣除法的相同,可准确识别沾染物类型,同时避免了背景扣除法对背景光谱的依赖。该方法简单可靠,测试迅速,有很大的应用潜力。     

猪肉组织的近场太赫兹成像检测研究

利用搭建的基于光电导微探针的近场太赫兹(Terahertz,THz)系统对新鲜猪肉组织切片进行了成像检测研究,结果发现近场THz成像可以很好地区分猪肉组织中的脂肪组织区域和肌肉组织区域,其成像效果明显优于传统远场THz时域光谱成像系统。研究表明了基于光电导微探针的近场THz成像技术在生物样品检测方面的可行性,展示出该技术在生物医学检测领域具有很好的应用前景。     

单激光源谐波遥感探测甲烷研究

提出了一种利用单一可调谐外腔二极管激光 (ECDL)及谐波探测技术对甲烷进行现场、实时遥感探测方案。通过理论推导计算出该方案在甲烷 2ν3 吸收带的R6支吸收线上理论最小可探测路径 积分浓度为 87× 10 -9。根据该方案建立了实验系统 ,实验结果验证了该方案的可行性并估算出实验最小可探测甲烷的路径 积分浓度为 4 2 0× 10 -9。     

基于压缩感知的地基MIMO SAR近场层析成像研究

合成孔径雷达(Synthetic Aperture Radar,SAR)层析技术是一种通过多航迹观测,获取目标高程信息,重建目标三维结构的重要手段。目前,层析SAR成像多应用于星载与机载平台,均以远场假设为基础,即认为雷达与目标间的距离远大于目标几何尺寸,此时多航迹观测雷达对目标的视角变化很小,目标的散射特征变化很小。但是在近场构型下,多航迹观测雷达对目标的视角变化大,目标的散射特征变化大,现有基于远场假设的层析处理方法不再适用。为解决这一问题,本文研究了基于压缩感知的地基多输入多输出(Multiple Input Multiple Output, MIMO)SAR近场层析成像方法,主要包含了以下方法创新:(1)基于孤立强点定标完成通道间幅相误差补偿,提高成像质量;(2)基于散射体结构信息与闪烁强点剔除实现高精度多图配准;(3)利用解斜思想与三维空间几何关系估计高程信息。最后,本研究实现了基于Ku频段MIMO SAR的建筑物三维结构反演。      

Real-time control of angioplasty balloon inflation based on feedback from intravascular optical coherence tomography: preliminary study on an artery phantom

A method is proposed to achieve computerized control of angioplasty balloon inflation, based on feedback from intravascular optical coherence tomography (IVOCT). Controlled balloon inflation could benefit clinical applications, cardiovascular research, and medical device industry. The proposed method was experimentally tested for balloon inflation within an artery phantom. During balloon inflation, luminal contour of the phantom was extracted from IVOCT images in real time. Luminal diameter was estimated from the obtained contour and was used in a feedback loop. Based on the estimated actual diameter and a target diameter, a computer controlled a programmable syringe pump to deliver or withdraw liquid in order to achieve the target diameter. The performance of the control method was investigated under different conditions, e.g., various flow rates and various target diameters. The results were satisfactory, as the control method provided convergence to the target diameters in various experiments.     

A reconstruction algorithm for breast cancer imaging with electrical impedance tomography in mammography geometry

The conductivity and permittivity of breast tumors are known to differ significantly from those of normal breast tissues, and electrical impedance tomography (EIT) is being studied as a modality for breast cancer imaging to exploit these differences. At present, X-ray mammography is the primary standard imaging modality used for breast cancer screening in clinical practice, so it is desirable to study EIT in the geometry of mammography. This paper presents a forward model of a simplified mammography geometry and a reconstruction algorithm for breast tumor imaging using EIT techniques. The mammography geometry is modeled as a rectangular box with electrode arrays on the top and bottom planes. A forward model for the electrical impedance imaging problem is derived for a homogeneous conductivity distribution and is validated by experiment using a phantom tank. A reconstruction algorithm for breast tumor imaging based on a linearization approach and the proposed forward model is presented. It is found that the proposed reconstruction algorithm performs well in the phantom experiment, and that the locations of a 5-mm-cube metal target and a 6-mm-cube agar target could be recovered at a target depth of 15 mm using a 32 electrode system.     

激光反射层析成像相位恢复算法研究

针对激光反射层析成像中目标随机抖动与径向运动造成的投影中心失配问题,提出采用相位恢复算法对重构图像进行相位恢复重建,通过反复光强迭代消除目标随机运动造成的相位误差,达到减少重构误差、恢复目标图像的目的。为改进G-S算法收敛速度与恢复精度,提出频域模值加权方法进行投影数据相位迭代恢复,仿真实验表明,将算法收敛速度与收敛精度提高了1.2倍以上。通过对三组仿真实验处理,重构图像的平均相对均方误差由2.487 5下降到0.792 7,有效地恢复了目标图像轮廓。外场实验表明,该算法能够有效消除重构图像伪迹,改善激光反射层析成像系统成像质量。     

基于红外光学层析物体被动态遮挡的边缘检测

针对导弹的红外凝视目标跟踪中存在被跟踪物体被动态遮挡的检测问题,采用光学层析的思想,借助傅里叶切片定理,对采集的目标数据进行线性积分后再进行傅里叶变换。光学层析成像中图像重建的实质是通过不同角度的投影信息确定成像平面上每个像素的实际光强分布。由于物体被动态遮挡,总有一个角度的投影可以将其他角度投影被遮挡部分填充,最后做二维傅里叶逆变换,即可得到重建后边缘完整的图像,该图像可以识别到完整的轮廓信息。     

Real-time control of angioplasty balloon inflation based on feedback from intravascular optical coherence tomography: experimental validation on an excised heart and a beating heart model

We report on real-time control of balloon inflation inside porcine arteries. In the first step, experiments were done in a coronary artery of an excised heart. In the second step, experiments were done in a beating heart setup providing conditions very close to in vivo conditions without the complications. A programmable syringe pump was used to inflate a compliant balloon in arteries, while intravascular optical coherence tomography (IVOCT) monitoring was performed. In a feedback loop, IVOCT images were processed to provide the balloon diameter values in real time to control the pump action in order to achieve a target diameter. In different experiments, various flow rates and target diameters were used. In the excised heart experiment, there was good convergence to target diameters resulting in a satisfactory balloon inflation control. In the beating heart experiment, there were oscillations in the diameter values due to cyclic arterial contractions. In these experiments, the control system maintained diameter averages satisfactorily close to predetermined target values. Real-time control of balloon inflation could not only provide a safer outcome for angioplasty procedures, but could also provide additional information for diagnostics since it implicitly provides information about the artery response to the inflation process.     

Reconstruction of attenuation map using discrete consistency conditions

Methods of quantitative emission computed tomography require compensation for linear photon attenuation. A current trend in single-photon emission computed tomography (SPECT) and positron emission tomography (PET) is to employ transmission scanning to reconstruct the attenuation map. Such an approach, however, considerably complicates both the scanner design and the data acquisition protocol. A dramatic simplification could be made if the attenuation map could be obtained directly from the emission projections, without the use of a transmission scan. This can be done by applying the consistency conditions that enable us to identify the operator of the problem and, thus, to reconstruct the attenuation map. In this paper, we propose a new approach based on the discrete consistency conditions. One of the main advantages of the suggested method over previously used continuous conditions is that it can easily be applied in various scanning configurations, including fully three-dimensional (3-D) data acquisition protocols. Also, it provides a stable numerical implementation, allowing us to avoid the crosstalk between the attenuation map and the source function. A computationally efficient algorithm is implemented by using the QR and Cholesky decompositions. Application of the algorithm to computer-generated and experimentally measured SPECT data is considered.     

基于电磁层析的地面目标内部结构图像重建

针对电磁层析成像技术在工程物探中, 采用钻孔方式进行地下介质内部结构探测有损的不足, 为适应电磁层析成像技术无损探测的需求, 研究了对地面目标内部结构探测的电磁层析成像技术, 基于电磁层析的探测方式、联合成像方法和图像重建技术, 为弥补跨孔探测方法应用于地面目标探测时, 其边界条件与传统的地下目标探测不同, 会对初至波的判断造成影响的不足, 采用时域有限差分法仿真分析了波的传播状态, 确定了初至波的提取方法, 给出了初至零点的判定方法, 并采用以上方法进行实验证实了对地上目标进行电磁层析成像的可行性和有效性.     

A new look at spotlight mode synthetic aperture radar astomography: imaging 3-D targets

A new 3D tomographic formulation of spotlight mode synthetic aperture radar (SAR) is developed. This extends the pioneering work of Munson et al. (1983), who first formally described SAR in terms of tomography but who made the simplifying assumption that the target scene was 2D. The present authors treat the more general and practical case in which the radar target reflectivities comprise a 3D function. The main goal is to demonstrate that the demodulated radar return data from a spotlight mode collection represent a certain set of samples of the 3D Fourier transform of the target reflectivity function and to do so using a tomographic paradigm instead of traditional range-Doppler analysis. They also show that the tomographic approach is useful in interpreting the reconstructed 2D SAR image corresponding to a 3D scene. Specifically, the well-known SAR phenomenon of layover is easily explained in terms of tomographic projections and is shown to be analogous to the projection effect in conventional optical imaging.     

光学层析成像技术的发展现状

光学层析成像技术对成像科学的发展具有变革传统技术的重大意义，它将在医学早期癌组织诊断、材料检测和军事模糊目标识别等方面具有广阔应用前景。综述了光学层析成像技术及发展现状，提出了发展中存在和要解决的问题。