Imaging photothermal microscopy for absorption measurements of optical coatings

For absorption measurement of large-aperture optical coatings, a novel method of imaging photothermal microscopy based on image lock-in technique is presented. Detailed theoretical analysis and numerical calculation are made based on the image photothermal technique. The feasibility of this imaging method is proved through the coincidence between the theoretical results of single spot method and multi-channel method. The measuring speed of this imaging method can be increased hundreds of times compared with that of the raster scanning. This technique can expand the applications of photothermal technique.     

激光二维扫描显示技术的研究

结合激光特性和电视扫描成像原理,提出一种二维激光光栅扫描方案,并实际建立一套光栅产生系统。通过实验得到均匀的扫描光栅,测得一组实验数据。对实验数据进行处理得到了振镜偏转角度和扫描频率之间具体的函数表达式及其图像表示,进而推导得到光栅大小和扫描频率之间的函数关系式。另外,对扫描光栅的特征参数进行了分析。     

Three-dimensional subwavelength imaging by a photonic-crystal flat lens using negative refraction at microwave frequencies

We experimentally demonstrate subwavelength resolution imaging at microwave frequencies by a three-dimensional (3D) photonic-crystal flat lens using full 3D negative refraction. The photonic crystal was fabricated in a layer-by-layer process. A subwavelength pinhole source and a dipole detector were employed for the measurement. By point-by-point scanning, we obtained the image of the pinhole source shown in both amplitude and phase, which demonstrated the imaging mechanism and subwavelength feature size in all three dimensions. An image of two pinhole sources with subwavelength spacing showed two resolved spots, which further verified subwavelength resolution.     

基于单光子脉冲时间随机性的光量子随机源

提出了一种基于单光子脉冲时间随机性的光量子随机源。利用衰减成单光子态的光强恒定光源和一个单光子探测器产生单光子随机脉冲,通过连续比较单光子随机脉冲序列中相邻两个脉冲的时间间隔来提取随机位。通过设计高速响应的微通道板单光子探测器和基于现场可编程门阵列(FPGA)的随机位提取电路,获得了超过10Mbit/s的随机位产生速率。通过采用恒比定时和对计数时钟倍频的方法提高时间间隔的测量精度,从而减小随机位序列的相关系数。当光量子随机源的随机位产生速率在10kbit/s以下时,所获得的二进制随机位序列的相关系数小于0.001。运用随机性测试程序ENT和DIEHARD对所获的随机位序列进行测试,测试结果表明序列的随机性非常好且不需要后续处理,完全满足真随机数的标准。     

腔光力学系统中的量子测量

腔光力学系统近年来迅猛发展, 在精密测量、量子传感等方面已展现出重要的应用价值. 特别是与微纳技术和冷原子技术结合后, 这一系统正发展成为研究量子测量与量子操控的理想平台. 本文首先综述腔光力学在量子测量, 尤其是量子测量基础理论研究方面的进展; 然后分析腔光力学系统中的量子测量原理; 最后介绍我们近来在这方面的研究进展, 并通过我们设计的一系列新颖的基于腔光力学系统的量子测量方案来具体展示该系统在量子测量、量子操控等方面的潜在应用.     

Improving the purity of heralded single-photon sources through spontaneous parametric down-conversion process

The high-purity single-photon source plays an important role in the field of quantum information. Usually, it is generated through spontaneous parametric down-conversion process. In this paper, we investigate and summarize a few approaches on obtaining single-photon sources with a high purity using either PPKTP or PPLN nonlinear crystals. Moreover, we present improved schemes to increase the purity based on existing work, corresponding applicable conditions and procedures are discussed and analyzed. Besides, we carry out numerical simulations and show that nearly perfect purity can be reached even without using any filters. Therefore, this work might provide valuable references for the generation and application of high purity single-photon sources.     

Guiding a confocal microscope by single fluorescent nanoparticles

Confocal optical microscopes offer unparalleled high sensitivity and three-dimensional (3D) imaging capability but require slow point-by-point scanning; they are inefficient for imaging moving objects. We propose a more efficient solution. Instead of indiscriminate scanning, we let the focus of the microscope pursue the object of interest such that no time is wasted on uninformative background, allowing us to visualize 3D trajectories of fluorescent nanoparticles in solution with millisecond temporal and ~200 nm spatial resolution.     

Closed-System Solution of the 1D Atom from Collision Model

Obtaining the total wavefunction evolution of interacting quantum systems provides access to important properties, such as entanglement, shedding light on fundamental aspects, e.g., quantum energetics and thermodynamics, and guiding towards possible application in the fields of quantum computation and communication. We consider a two-level atom (qubit) coupled to the continuum of travelling modes of a field confined in a one-dimensional chiral waveguide. Originally, we treated the light-matter ensemble as a closed, isolated system. We solve its dynamics using a collision model where individual temporal modes of the field locally interact with the qubit in a sequential fashion. This approach allows us to obtain the total wavefunction of the qubit-field system, at any time, when the field starts in a coherent or a single-photon state. Our method is general and can be applied to other initial field states.     

量子密码通信中量子比特率理论分析

在量子密钥分配中,量子比特率是一个重要的系统参数。通过引入测量因子和筛选因子,建立了基于理想单光子源和泊松分布单光子源的量子比特率理论模型,给出了量子比特率的表达式,并对两种单光子源进行了比较分析。结果表明,当平均光子数大于1时,泊松分布单光子源能被优化。在发射机脉冲重复率一定的条件下,采用泊松分布单光子源无法达到理想单光子源的量子比特率,这是为保密通信所必须付出的代价。     

Dark-field scanning in situ spectroscopy platform for broadband imaging of resected tissue

A dark-field geometry spectral imaging system is presented to raster scan thick tissue samples in situ in 1.5 cm square sections, recovering full spectra from each 100 μm diameter pixel. This spot size provides adequate resolution for wide field scanning, while also facilitating scatter imaging without requiring sophisticated light-tissue transport modeling. The system is demonstrated showing accurate estimation of localized scatter parameters and the potential to recover absorption-based contrast from broadband reflectance data measured from 480 nm up to 750 nm in tissue phantoms. Results obtained from xenograft pancreas tumors show the ability to quantitatively image changes in localized scatter response in this fast-imaging geometry. The polychromatic raster scan design allows the rapid scanning necessary for use in surgical/clinical applications where timely decisions are required about tissue pathology.     

超导单光子探测器件直流特性研究

超导单光子探测技术是基于超薄超导薄膜的非平衡态热电子效应的一种新型的单光子探测方法。超导单光子探测器(SNSPD)的计数率可达到GHz,时间抖动小于100ps,因而在未来量子通信系统中有着广阔的应用前景。介绍了NbN超导单光子探测器件的工作原理和器件超导性能测试系统;测试了超导单光子探测器件的电阻-温度、电流-电压等特性。并对测试结果进行了分析和讨论。     

基于无衍射光的表面粗糙度三角测量及其灰色评定方法

 激光三角法是表面形貌非接触测量中的一种常用方法,在几何测量领域应用广泛。传统的激光三角法采用高斯光束作为指示光源,在机械扫描机构的配合下,通过对被测表面逐点扫描完成表面形貌的测量。采用新型的无衍射光替代传统激光光源,解决了普通高斯光束存在的“焦深”问题,简化了机械结构。并采用基于灰色系统理论的灰色滤波进行表面形貌的分离与评定,克服了原有方法对测量数据样本量和统计特性的依赖,并通过实验表明该系统能够准确地完成表面形貌的三维测量,所提出的灰色评定方法能够比较有效地进行表面形貌的分离与评定。     

水下同步扫描三角测距成像理论建模及仿真分析

针对激光同步扫描三角测距成像系统水下应用时,考虑不同介质界面的折射效应,通过理论建模,得出水下同步扫描三角测距成像系统的空间三维坐标测量关系表达式。分析了基线距离、接收透镜焦距等系统主要参数对距离测量分辨率的影响,以及成像探测器长度对测量范围的影响。仿真结果表明:增大基线距离和接收透镜焦距,有利于提高距离测量分辨率,增加成像探测器长度,有利于增大系统测量范围,为水下同步扫描三角测距成像系统的设计提供了理论依据。     

通信波长频率一致纠缠光源的频谱测量

本文利用光栅单色仪实现了对超短脉冲抽运周期极化磷酸氧钛钾晶体产生的通信波长频率一致纠缠光子源的频谱特性分析.测量到双光子的联合频谱呈正关联分布,为频率一致纠缠光源.信号光、闲置光中心波长分别为1574.4 nm和1574.9 nm,频谱宽度分别为35.3 nm和37.6 nm,双光子符合包络宽度约为3 nm.根据单光子频谱宽度与双光子符合包络宽度的比值可以得到双光子的频率纠缠参量R约为12,表征了信号光子与闲置光子之间具有较高的频率纠缠度.     

纠缠光子法绝对定标光电探测器量子效率的研究

为了应对国际上“坎德拉”新定义的动向,开展了利用纠缠光子法测量光电探测器量子效率的研究,并建立了测量装置。装置采用351.1 nm连续激光抽运BBO晶体产生纠缠光子场,然后通过双通道门控计数器组成的符合测量系统在702.2 nm和788.7 nm两个波长点对光电倍增管的量子效率进行了测量。同时对单光子脉冲信号获取、噪声抑制及提取、符合时间特性、偶然符合、暗背景计数和器件透过率等影响测量结果的关键因素进行了实验分析并给出了修正分量,最终在两个波长点量子效率测量不确定度小于0.7%。     

Generation and Detection of Infrared Single Photons and their Applications

Unbreakable secret communication has been a dream from ancient time. It is quantum physics that gives us hope to turn this wizardly dream into reality. The rapid development of quantum cryptography may put an end to the history of eavesdropping. This will be largely due to the advanced techniques related to single quanta, especially infrared single photons. In this paper, we report on our research works on single-photon control for quantum cryptography, ranging from single-photon generation to single-photon detection and their applications.     

基于伪态协议的量子密钥分配系统研究

采用包含两个伪态和一个信号态的双伪态协议分析了量子密钥分配系统的性能,比较了双伪态（真空态—弱伪态）和单伪态协议条件下密钥生成率与通信距离的关系,分析了信号态的强度、量子比特误码率、单光子的增益和单光子的误码率对系统密钥生成率的影响,得出密钥生成率的最优化条件,为实现实用安全的量子密钥分配系统奠定理论基础. 关键词： 伪态协议 量子密钥生成率 量子比特误码率     

激光雷达扫描方式

为实现激光束对空域的有效扫描和探测,研究了栅形扫描、李萨茹形扫描、螺旋形扫描和六边形扫描四种常见的激光雷达扫描方式,推导了相应的扫描方程,讨论了参数的物理意义及调整方法;重点研究了栅形扫描和六边形扫描方式下光斑的分布情况,通过仿真分析了两种扫描方式下光束的漏扫率和重叠率,结果表明,在相同扫描条件下六边形扫描方式的漏扫区域最少。展示了基于上述研究内容的扫描控制系统实物图及扫描图案。分析总结了四种扫描方式的特点,给出了每种扫描方式的适用情况及使用建议。     

基于Walsh-Hadamard变换的单像素遥感成像

本文提出了基于Walsh-Hadamard变换的单像素成像方案, 并从理论分析、模拟仿真和实验验证三方面分别验证了该方案的可行性. 实验上实现了350-900 nm波段对 距离500 m和5000 m自然目标的128×128 像素成像, 成像速度0.5帧/秒. 研究并讨论了单像素相机方案与计算量子成像方案的差异与共性, 在此基础上分析了基于Walsh-Hadamard变换的单像素成像方案的优势与局限性. 研究表明本方案同时适用于单像素相机和计算量子成像. 由于单像素成像适用于应用在如红外热成像、微波成像等波段, 因此在阵列探测器灵敏度或工艺达不到要求时存在优势. 本文所提出的方案使得单像素成像技术向实际应用迈进了一步.     

Hyperentanglement-assisted hyperdistillation for hyper-encoding photon system

In quantum information processing, the quality of photon system is decreased by the inevitable interaction with environment, which will greatly reduce the efficiency and security of quantum information processing. In this paper, we propose hyperentanglement-assisted hyperdistillation schemes to guarantee the quality of hyper-encoding photon system based on the method of quantum hyper-teleportation, which can increase the success probability of hyperdistillation and reduce the resource consumption. First, we propose a hyperentanglement-assisted single-photon hyperdistillation (HASPHD) scheme for polarization and spatial qubits to get rid of the vacuum state component caused by transmission loss, whose success probability can achieve the optimal one by increasing the efficiency of quantum hyper-teleportation. Subsequently, we present two hyperentanglement-assisted hyperentanglement distillation (HAHED) schemes for photon system to protect hyperentanglement from both transmission loss and quantum channel noise, which can recover the less-entangled mixed state to maximally hyperentangled state for known-parameter and unknown-parameter cases with high success probability and low resource consumption. In these hyperdistillation schemes, the influence of imperfect effects of optical elements can be largely decreased by the quantum hyper-teleportation method. These characters make the hyperentanglement-assisted hyperdistillation schemes have potential application prospects in practical quantum information processing.