压缩感知光谱测量局部哈达玛矩阵的构造与性能

针对压缩感知光谱测量中随机矩阵作为测量矩阵无法获得高质量重建精度问题,提出了一种测量矩阵构造的新方法。介绍了局部哈达玛矩阵的构造方法,以随机测量矩阵为比较对象,通过仿真实验对局部哈达玛矩阵在压缩感知光谱测量中的性能进行分析。实验结果表明,相对于随机矩阵,新型局部哈达玛矩阵下的重建光谱与原始光谱重合度大大提高,在100%采样率时,定量指标MSE为3.2,实现了光谱的精确重建,25%采样率的MSE指标水平已经与随机矩阵100%采样率时相当,局部哈达玛矩阵可以有效的改善光谱重建的精度;光谱重建时间大约缩短到1/3,系统具有更好的信噪比特性。     

相控阵超声缺陷检测数据压缩感知

为了解决超声相控阵信号采集、存储和传输中数据量大的问题,研究了压缩感知在相控阵无损检测信号和图像压缩重构中应用的可行性。首先使用5种贪婪算法对相控阵仿真信号进行压缩重构,根据百分比均方误差选取最优算法并考虑了噪声对精度的影响,结果表明压缩感知可以用低于奈奎斯特极限的测量点数准确重构原始图像;其次用人工缺陷回波信号进行实验验证,通过稀疏度计算选择适用相控阵信号的最优稀疏基,并通过5种传感矩阵的优化选择进一步提高了重构精度。实验结果尽管达不到仿真中的理想效果,但是能以少量测量值准确恢复图像,并能保证缺陷的识别,说明压缩感知算法可以有效提高相控阵缺陷检测效率。此外,在保持测量点数相同的情况下,仿真和实验都研究了不同采样率对重构精度的影响,当测量点数超过一定值时,证实了压缩感知实际与采样率无关。      

动态光谱频域提取的FFT变换精度分析

近红外光谱无创血液成分检测因其测量方法的优越性,已经成为生物医学领域的研究热点之一.但除血氧饱和度外,目前还没有进入临床应用成果的报道,其关键在于个体差异和测量条件对检测精度的影响.文章先介绍一种可以消除个体差异的新的检测方法--动态光谱法,再从其原理出发,推导出基于傅里叶变换的动态光谱频域提取法.同时,文章通过实验,研究了采样率,采样周期个数,非同步采样对(快速傅里叶变换(FFT)精度的影响.分析结果表明:选择合适的采样率,采样信号周期个数、并利用现有的加窗和插值算法能够大幅度提高动态光谱数据的精度.     

基于自适应条纹投影的彩色物体三维形貌测量

针对三维形貌测量技术中彩色物体表面反射率的非均匀性影响测量结果的问题,提出一种基于自适应条纹投影的三维形貌测量技术,该方法可避免彩色物体表面反射率非均匀的影响,提高系统的测量精度。彩色相机采集RGB光强图像,并根据物体表面颜色的反射特性计算每个像素点的最优投射光强和颜色;采集水平和垂直的正弦条纹序列,利用计算所得绝对相位值将相机图像坐标系中每一个像素点的最优投射光强和颜色映射到投影仪像素坐标系;投射自适应条纹序列进而测量彩色物体的三维形貌。实验结果表明,该方法能够有效测量彩色物体三维形貌,具有很高的测量精度。     

紫外波段高光谱太阳参考光谱时变模型研究

太阳参考光谱是星上辐射定标和波长定标的基准。太阳活动周期内,太阳辐照度光谱幅值存在周期性波动,紫外波段光谱幅值变化达10%以上,相对于3%的星上绝对定标需求,太阳的时变特性不可忽略。针对不同分辨率和采样率的太阳参考光谱,首先研究了插值间隔和卷积间隔对计算MgII参数的数值影响,通过分析比较后选择合适的插值、卷积间隔,并基于Climate和SORCE的MgII参数时间序列完成太阳周期性变化建模。然后选择2003年8月21日至2012年4月15日期间80组数据,每组包含2个不同日期的不同波长的辐照度光谱幅值和MgII值,针对该80组数据使用一阶拟合取代比值方法计算得到转换因子,将不同日期的太阳参考光谱幅值修正到同一日期并与实际观测真值比较;结果表明了一阶拟合与比值方法相比有着更高的反演精度及预测精度。最后,基于一阶拟合转换因子和MgII参数时间序列对现有光谱进行时间和格式归一化,通过分波段筛除偏离较大光谱数据的方法构建了2008年6月25日,分辨率为1 nm、采样率为0.1 nm的太阳参考光谱。原有的12条光谱经过筛除后,留下全波段均位于中位的光谱6条,所构建的光谱同筛选出的6条光谱平均值相比,绝对误差在0.982%以内。所构建的光谱可以通过MgII参数时间序列和转换因子计算得到任意日期下的光谱。针对该参考光谱利用KNMI高光谱进行分辨率和采样率提升,最终基于我国计划发射的风云三号紫外高光谱臭氧探测仪(OMS)在轨观测和星上定标需求,构建得到了波长范围250～500 nm,分辨率0.1 nm,采样率0.01 nm的太阳参考光谱。     

基于光时分复用技术的高速成像系统北大核心CSCD

提出了一种基于光时分复用技术的高速成像系统。飞秒激光器中心波长1557nm,脉冲宽度90fs,对USAF-1951分辨率板线性扫描成像,扫描频率为38.88 MHz。在连续时间序列编码放大显微成像技术的基础上,运用光时分复用技术,复制光脉冲信号并携带检测物体相同的空间信息。原光脉冲和复制光脉冲以相同的采样率分别采样,通过相应的数据处理将两次采样数据整合在一起还原图像。实验结果表明,与传统的超快成像方法相比,成像系统利用10GHz的数字采样设备可以达到20GHz的采样率,采样点数是传统超快成像方法的两倍。该方法有效克服了成像系统采样率不足的问题,提高了成像系统的空间分辨率。与此同时,该系统算法复杂程度不高,有利于进一步促进超高速成像技术的发展。     

测量石英晶体光轴方向厚度的光谱分析法

基于石英晶体的旋光色散原理,提出了一种测量石英晶体光轴方向厚度的光谱分析方法。利用光学矩阵方法对测量原理进行了分析,指出通过测量由两个正交的偏光镜和待测石英晶体所组成的系统的透射曲线就可以精确计算出待测石英晶体的厚度。在实验的过程中进行了误差分析,分析表明选取长的测量波段、低的扫描速度、短的响应时间和小的狭缝宽度都有利于提高测量精度,并从理论上证明所得厚度的精度高于电子数显千分尺的测量精度。利用三种不同的方法对两块不同厚度的石英晶体进行了测量,测量结果表明利用提出的方法所得厚度的精度可以达到0.1μm,与理论分析的结果相一致。     

一种提高激光波长测量精度的改进算法

分析了一种激光波长测定装置对波长较长的激光测量精度难以提高的原因,提出了用离散傅里叶变换精确测定有限长周期序列信号频率的改进算法.仿真结果表明:此算法切实可行,且有利于该装置测量精度的提高和测量范围的扩大.     

基于角度散射法的气溶胶粒子粒径分布反演研究

本文基于人工蜂群-差分近似优化算法(Artificial Bee Colony and Differential Evolution algorithm, ABC-DE)和角度光散射法对气溶胶粒径分布进行了反演研究。此外,本文还提出了一种基于敏感度分析和主成分分析的角度散射测量信号筛选方法,用以提高粒径分布反演结果精度。研究表明:采用角度散射法反演颗粒粒径分布时,选择前向散射角度,如[0°,30°],更有利于提高反演结果精度;粒径分布反演精度与所选择测量角度信号的贡献率相关,高贡献率的测量信号更有利于确保反演结果精度和鲁棒性。     

双目立体视觉测距系统误差模型的研究

针对双目立体视觉测距中产生误差的问题,分析了系统中的各个参量,并建立了双目立体视觉测距系统的误差模型。得出引起测量系统误差最大的两个参量是CCD摄像头的对准程度和测量的距离;在视场中心的距离测量精度低,边缘测量精度高,在视场中心的水平和纵向的测量精度却远高于在边缘的测量精度两个结论。基于本文建立的误差模型可以指导适用于具体应用场合的双目立体视觉测距系统的设计。     

Attosecond‐precision ultrafast photonics

We review our recent progress toward attosecond‐precision ultrafast photonics based on ultra‐low timing jitter optical pulse trains from mode‐locked lasers. In femtosecond mode‐locked lasers, the concentration of a large number of photons in an extremely short pulse duration enables the scaling of timing jitter into the attosecond regime. To characterize such jitter levels, we developed new attosecond‐resolution measurement techniques and show that standard fiber lasers can achieve sub‐fs high‐frequency jitter. By leveraging the ultra‐low jitter of free‐running mode‐locked lasers, we pursued high‐precision optical‐optical and optical‐microwave synchronization techniques. Optical signals spanning 1.5 octaves were synthesized by attosecond‐precision timing and phase synchronization of two independent mode‐locked lasers. High‐stability microwave signals were also synthesized from mode‐locked lasers with drift‐free sub‐10‐fs precision. We further demonstrated the attosecond‐precision distribution of optical pulse trains to remote locations via timing‐stabilized fiber links. Finally, the application of optical pulse trains for high‐resolution sampling and analog‐to‐digital conversion is discussed.     

Broadband interference of received pulse for single normal mode and solitary internal wave localization

To analyze the solitary internal wave(SIW) influence on acoustic field interference pattern and thereby monitor SIW, for broadband pulse signal propagating through SIWs, we adopt a parabolic equation model, and simulate the variation of received single normal mode(SNM) pulse sequence with SIW position, and analyze the spatiotemporal interference characteristics and mechanism of the sequence. Based on the coupled mode theory, we derive the relationship between SIW position and interference striation slope(ISS). The relationship can monitor the SIW position precisely, with greatly improved precision and robustness compared with previous work. Furthermore, based on the SNM interference pattern periodicity in frequency, we also develop another method to estimate SIW range, with better real-time property than the first method. The SIW-normal mode interference relationship can be used for improving acoustic field localization in the presence of SIWs, which has great value for oceanology,marine engineering, marine military and so on. Besides, the relationship can be expanded to other detection for local variation, e.g., detecting metal flaw and locating dramatic variation in seabed topography.     

单阶简正波宽带干涉特性与孤立子内波定位

为了分析孤立子内波(SIW)对声场干涉特性的影响以及由此监测SIW,我们采用抛物方程模型,分析了孤立子内波影响下简正波耦合带来的单阶简正波宽带脉冲序列的干涉特性;仿真了宽带脉冲信号穿过SIW时,单阶简正波接收脉冲序列随内波位置的变化情况,分析了它们的时空干涉特性和机理;基于耦合简正波理论,推导得到了内波位置和干涉条纹斜率之间的关系。仿真表明,这一关系式可以精确估计SIW距离,估计精度和稳定性比以往方法大大提升。此外,还根据单阶简正波干涉图样在频率上的周期性,推导了另一种估计SIW距离的方法,该方法具有更好的实时性。SIW-简正波干涉关系可用于改善声场定位,对于海洋学、海洋工程和海洋军事等方面具有重要价值。此外,该关系还可以拓展到其他的局部特性变化的探测,如金属探伤和海底地形突变定位等。      

基于FPGA和DSP的微型惯导系统

 惯导系统的硬件组成直接影响到系统的体积和解算速度,构建合理的硬件系统直接关系到惯导系统的精度指标。针对某小型惯导系统对体积和解算精度的特殊要求,解决已有微型惯导系统的方案缺陷,提出一种工程实用强的惯导系统。该系统用FPGA作为采集控制惯性传感器的核心芯片,设计了并行采集方案,32位浮点型高速DSP实现惯导解算。经过转台测试与外场试验表明：系统具有抗干扰能力强、实时响应迅速、惯性单元标定简便、易实现等优点,系统指标完全满足原设计要求。     

Non-Geometric Conditional Phase Gate by Quantum Zeno Dynamics in Laser-Excited Nitrogen-Vacancy Centers

Based on the quantum Zeno dynamics,we propose a two-qubit non-geometric conditional phase gate between two nitrogen-vacancy centers coupled to a whispering-gallery mode cavity.The varying phases design of periodic laser can be used for realizing non-geometric conditional phase gate,and the cavity mode is virtually excited during the gate operation.Thus,the fidelity of the gate operation is insensitive to cavity decay and the fluctuation of the preset laser intensity.The numerical simulation with a realistic set of experimental parameters shows that the gate fidelity 0.987 can be within reached in the near future.     

基于高速肖特基二极管的100 ps瞬态取样门设计与仿真

 皮秒级瞬态取样门主要应用于激光聚变实验和高能物理实验中，对单次高速脉冲进行实时取样。提出了一种新颖的基于肖特基二极管桥的平衡取样门，给出其模型和具体电路设计。电路仿真结果表明，对称的选通设计保证了选通脉宽为100 ps时，取样间隔也为100 ps，取样门带宽为4.4 GHz，可应用于多路超短激光脉冲取样。     

空间采样傅里叶变换光谱仪光谱反演研究

根据相似性准则,对采集到的干涉图像进行干涉图元的拆分,通过寻址定位,得到与离散光程差序列相匹配的采样干涉图序列。采用过零采样方式,对大单边干涉图序列与小双边干涉图序列利用不同的窗函数进行切趾。为了校正相位误差,结合所研究采样干涉图的特点,对频域光谱乘积校正和空域干涉图卷积校正进行了研究和改进,获得了比较理想的光谱线形,其中空域干涉图卷积校正后的光谱偏差仅为0.012088,具有最好的校正效果。     

Defining optimal axial and lateral resolution for estimating scatterer properties from volumes using ultrasound backscatter

The rf signals used to construct conventional ultrasound B-mode images contain frequency-dependent information that can be examined through the backscattered power spectrum. Typically, the backscattered power spectrum is calculated from a region of interest (ROI) within some larger volume. The dimensions of the ROI are defined axially by the spatial length corresponding to the time gate and laterally by the number of scan lines included in the ROI. Averaging the backscattered power spectra from several independent scan lines can reduce the presence of noise caused by electronics and by the random scatterer spacings, but also decreases the lateral resolution of the interrogation region. Furthermore, larger axial gate lengths can be used to reduce the effects of noise and improve the precision and accuracy of scatterer property estimates but also decreases the axial resolution. A trade-off exists between the size of the ROI (the number of scan lines used, the separation distance between each scan line, the axial gate length) and the accuracy and precision of scatterer property estimates. A series of simulations and measurements from physical phantoms were employed to examine these trade-offs. The simulations and phantom measurements indicated the optimal lateral and axial sizes of the ROI, where estimate accuracy and precision were better than 10% and 5%, respectively, occurred at 4 to 5 beamwidths laterally and 15 to 20 spatial pulse lengths axially.     

Experimental Realization of Arbitrary Accuracy Iterative Phase Estimation Algorithms on Ensemble Quantum Computers

We report the first experimental demonstration of a nuclear phase estimation algorithms. Using feedback and iterations, magnetic resonance （NMR） realization of iterative we experimentally obtain the phase with 6 bits of precision on a two-qubit NMR quantum computer. Furthermore, we experimentally demonstrate the effect of gate noise on the iterative phase estimation algorithm. Our experimental results show that errors of measurements of the phase depend strongly on the precision of coupling gates. This experiment can be used as a benchmark for multi-qubit realizations of quantum information processing and precision measurements.     

Information-Efficient,Off-Center Sampling Results in Improved Precision in 3D Single-Particle Tracking Microscopy

In this work, we present a 3D single-particle tracking system that can apply tailored sampling patterns to selectively extract photons that yield the most information for particle localization. We demonstrate that off-center sampling at locations predicted by Fisher information utilizes photons most efficiently. When performing localization in a single dimension, optimized off-center sampling patterns gave doubled precision compared to uniform sampling. A ~20% increase in precision compared to uniform sampling can be achieved when a similar off-center pattern is used in 3D localization. Here, we systematically investigated the photon efficiency of different emission patterns in a diffraction-limited system and achieved higher precision than uniform sampling. The ability to maximize information from the limited number of photons demonstrated here is critical for particle tracking applications in biological samples, where photons may be limited.