荧光寿命的快速傅里叶变换拟合方法

介绍了一种利用快速傅里叶变换算法对稀土掺杂物质的荧光寿命进行数据拟合的方法。稀土掺杂物质可用来制备多种光学传感器,用于温度、pH值等多种参量测量领域。本方法利用快速傅里叶变换(FFT)结果作为基础,从非零项的相位角的正切值得出被测的荧光寿命,具有速度快、误差小、不受本底干扰等一系列优点。以掺铒光纤为例,通过数字仿真将本方法与其它几种传统的拟合方法进行了比较。快速傅里叶变换方法的测量偏差不到Prony方法的50％,为对数似合(log-fit)方法测量偏差的1／6。另外,快速傅里叶变换方法由于不受本底噪声影响,可以不必在信号处理时去掉本底噪声,因而可以明显缩短测量时间。     

基于小波变换的蓝宝石荧光光纤温度计

采用激光加热小基座法生长出掺Cr3+的蓝宝石光纤荧光温度传感头，它具有结构紧凑，耐高温等特点，测温范围从室温到450℃。使用基于小波变换的数据处理方法，有效去除信号中的噪声，提高了信噪比。在对荧光测温机理和有关光纤技术进行分析的基础上，采用与调制荧光信号相关的双参考源相位锁定测量方案，可在无激励光干扰的情况下对荧光寿命进行实时测量。根据噪音和信号在小波变换下表现出的不同性质，提出以小波变换为基础的温度信号特征提取及消噪方法。与其它处理方法相比，小波变换方法可以克服傅里叶变换对突变信号不起作用的缺点，同时又比Gabor变换具有可变窗口的优点。该方法可以缩短测量时间，提高测量分辨率。     

泵浦蓝宝石光纤荧光温度传感器

采用激光加热基座法制备端部Cr3＋离子掺杂的蓝宝石单晶光纤,得到一体型蓝宝石单晶光纤荧光温度传感头.对所制备的荧光温度传感头的荧光温度特性进行了实验研究.结果表明,随着温度升高Cr3＋∶Al2O3单晶光纤荧光寿命单调下降,从温度为0 ℃的4.0 ms下降到450 ℃的0.2 ms.利用所制备的荧光温度传感头,用波长405 nm紫色LED作为泵浦光源,采用相关检测技术在线实时测量荧光寿命,研制成测温范围0 ℃～450 ℃一体型蓝宝石光纤荧光温度传感器.     

Measurement of decay time based on FFT

Decay time is an important parameter in fluorescence temperature and pH value measurement. Many approaches are developed based on different principles. The decay acquisition and estimation method is one of them. A novel estimation method is given in this paper, based on the fast Fourier transform (FFT). The decay time can be calculated from the frequent items of the FFT. The advantages of this method include high accuracy, quick processing, independence on base offset etc. A set of experiment results is obtained based on this method.     

一种测量高温中间包的蓝宝石光纤温度计

介绍了一种测量高温的蓝宝石光纤温度计.蓝宝石单晶光纤由于其极好的高温物理化学性能,适用于高温下光纤测温应用,可用作辐射型光纤温度传感器.蓝宝石光纤温度计采用激光加热小基座法生长出端部掺Cr3+的蓝宝石光纤荧光温度传感头.用激光加热小基座,把对荧光有温度反应的材料如红宝石晶体光纤生长在蓝宝石光纤上,制成具有结构紧凑,耐高温,功能稳定的传感探头.通过荧光寿命的检测,可以测量所对应的温度.根据表面温度,可以依据温度场得到内部温度,用于测量连铸炉中的中间包钢水温度,并给出了温度计的实验系统以及原始实验数据.实验数据表明,此结果精度高,可实现非接触测量.     

A portable shifted excitation Raman difference spectroscopy system: device and field demonstration

In this paper, we present a portable shifted excitation Raman difference spectroscopy (SERDS) system applied in outdoor experiments. A dual‐wavelength diode laser emitting at 785 nm is used as excitation light source. The diode laser provides two individually controllable excitation lines at 785 nm with a spectral distance of about 10 cm⁻¹ for SERDS. This monolithic light source is implemented into a compact handheld Raman probe. Both components were developed and fabricated in‐house. SERDS measurements are performed in an apple orchard, and apples and green apple leafs are used as test samples. For each excitation wavelength, a single Raman spectrum is measured with 50 mW at the sample. Strong background interference from ambient daylight and laser‐induced fluorescence obscure the Raman signals. SERDS efficiently separates the wanted Raman signals from the disturbing background signals. For the Raman spectroscopic investigations of green leafs, one accumulation with an exposure time of 0.2 s was used for each excitation wavelength to avoid detector saturation. An 11‐fold improvement of the signal‐to‐background noise is achieved using SERDS. The results demonstrate the suitability of the portable SERDS system for rapid outdoor Raman investigations. Copyright © 2016 John Wiley & Sons, Ltd.     

光纤应变监测系统的数据处理方法研究

光纤应变监测系统的数据不可避免的存在噪声,导致系统的虚假预警。为了有效的消除数据噪声,提高数据准确性,减小系统的预警误报,提出了一种新的数据处理方法。首先对应变数据进行小波多层滤波处理,然后用FFT低通滤波获得信号的轮廓,再用小波滤波后的信号减去FFT低通滤波后的信号,得到消除温度影响后的应变变化信号。结果表明：该方法能够有效减小温度与噪声的影响,提高光纤应变监测系统的准确率。     

热像仪空间NETD测量技术

凝视阵列型热像仪的空间噪声制约着热像仪对远距离目标的探测、分辨、跟踪性能。为解决热像仪空间噪声实际测量问题,分析了热像仪的空间噪声测量原理,给出了热像仪基于信号传递函数的空间噪声测量数学模型,介绍了热像仪某一组、某一区域或全部像素如何剔除时间域NETD,再通过统计计算得到其空间NETD的数学模型。对制冷型MCT320256凝视列阵热像仪的SiTF和空间NETD进行测量,当背景黑体温度为5 ℃时,FOV区域中心信号传递函数（SiTF）为27.29 mV/℃,NETD为0.128 ℃,20 ℃时FOV区域中心SiTF为29.03 ℃,NETD为0.121 ℃。测量结果表明:该方法可评估空间噪声对热像仪性能的影响。     

87Rb D1线法拉第反常色散光学滤波

为了得到在高背景噪音下对弱信号光的提取,实验研究了基于⁸⁷Rb D₁线5S_1/2F=2→5P_1/2 F'=1跃迁的795 nm法拉第反常色散光学滤波器.充铷的样品池所含⁸⁷Rb的比例高于自然铷,样品池处在均匀的磁场中并且夹在两个相互正交的偏振片之间.入射的探测光通过样品池,与原子相互作用,由于法拉第旋转效应实现滤波功能.改变实验条件,透射结果随之明显变化.当温度从340 K升高到360 K,透射谱的变化情况被细致记录,并且分析了导致透射情况变化的原因.在适当的工作温度以及磁场条件下,得到线宽为约220 MHz的超窄带透射谱线,谱线透过率约为48%.⁸⁷Rb D₁线的实验结果优于⁸⁵Rb的吸收线.     

A robust method for automated background subtraction of tissue fluorescence

This paper introduces a new robust method for the removal of background tissue fluorescence from Raman spectra. Raman spectra consist of noise, fluorescence and Raman scattering. In order to extract the Raman scattering, both noise and background fluorescence must be removed, ideally without human intervention and preserving the original data. We describe the rationale behind our robust background subtraction method, determine the parameters of the method and validate it using a Raman phantom against other methods currently used. We also statistically compare the methods using the residual mean square (RMS) with a fluorescence‐to‐signal (F/S) ratio ranging from 0.1 to 1000. The method, ‘adaptive minmax’, chooses the subtraction method based on the F/S ratio. It uses multiple fits of different orders to maximize each polynomial fit. The results show that the adaptive minmax method was significantly better than any single polynomial fit across all F/S ratios. This method can be implemented as part of a modular automated real‐time diagnostic in vivo Raman system. Copyright © 2007 John Wiley & Sons, Ltd.     

铷原子气体自旋噪声谱的测量与改进

利用自主设计并制作的基于现场可编程门阵列的实时傅里叶变换采集卡(FFTsDAC),采用线偏振光检测碱金属铷原子气样品中的自旋随机涨落(即自旋噪声谱).详细讨论了背景噪声以及自旋噪声随探测光光强的变化关系,证实了自旋噪声来自于系统中自旋的随机涨落.对比了两种FFTsDAC(8 bit采样的FFTsDACl和12 bit采样的FFTsDAC2)的测量性能,分析了影响实验信噪比的因素.FFTsDAC2具有更高的测量效率和采样深度以及更长的单次采样时间,因而具有更高的信噪比和更好的频率分辨率,与数值模拟的结果一致.     

Background removal from polarized Raman spectra of tooth enamel using the wavelet transform

A wavelet transformation method is introduced to remove the large fluorescence background from polarized Raman spectra of stained tooth enamel. This method exploits the wavelet multiresolution decomposition where the experimental Raman spectrum is decomposed into signals with different frequency components, and where the lowest frequency background and highest frequency noise are removed. This method is optimized using a simulated collection of parallel‐polarized and cross‐polarized Raman spectra of the enamel and then applied to a set of experimental data. The results show that the wavelet transform technique can extract the pure spectra from background and noise, with the depolarization ratio used to discriminate between early dental caries and sound enamel preserved. Copyright © 2010 Crown in the right of Canada. Published by John Wiley & Sons, Ltd.     

Optimized temperature measurement with time-of-flight method

Driven by resonance probe light background Rubidium gas can emit fluorescence, which interacts with the falling atomic cloud in the temperature measurement with the time-of-flight (TOF) method and influence the experimental results. The dependencies of the acceleration and the temperature of the atomic cloud on the detuning of the probe beams were studied. We propose that the deviation of the acceleration from the gravity acceleration can be taken as a criterion of the accuracy of the temperature measurement using TOF method. Moreover, using the principle of the radiation force on the cold atomic cloud, one may measure the considerably weak intensity of the fluorescence.     

Noise in a coupling electromagnetic detecting system for high frequency gravitational waves

This paper discusses the basic categories of noise in detecting high frequency gravitational waves in the microwave band (～0.1--10 GHz), which contain shot noise from the laser and the thermal radiation photons, thermal noise from statistical fluctuation of the thermal photons and fluctuation of the temperature, radiation press noise on the fractal membrane, the noise caused by the scattering of the Gaussian Beam (GB) in the detecting tube and noise in the microwave radiometers. The analysis shows that a reasonable signal-to-noise ratio may be achieved for a detecting device with the fixed power of GB (10⁵ W), only when the temperature of the environment is no more than T=1 K, and the optimal length of the microwave radiometers is about 0.3 m.     

Design of a stripline kicker for tune measurement in CSNS RCS

For CSNS RCS tune measurement, tune value is measured by exciting the bunch with a strip-line kicker fed with white noise and using a FFT algorithm. This article simulates the strip-line kicker in RCS and the efficiency of the kicker is discussed in a Matlab environment. The parameters of the kicker with an arc electrode structure such as a VSWR, wake impedance, and thermal state are analyzed based on the advantages of this design.     

Thermal Conductivity Measurement of Gases by the Transient Short-Hot-Wire Method

Measurements of the thermal conductivity of helium and hydrogen are performed using the transient short-hot-wire method. The short hot wire is made of platinum and has a diameter of about 10 μm and a length of about 15 mm. It is attached by spot welding to platinum terminals with a diameter of 1.5 mm. The probe is inserted into the sample vessel that has a volume of 35 cm³ and an inner diameter of 30 mm. The thermal conductivity is evaluated by comparing a numerical solution of the heat conduction in and around the short wire with the experimentally obtained temperature rise of the wire. The measured thermal conductivities show good reproducibility. Also, the measured thermal conductivities agree with the reference equations within a deviation of ± 1%.     

Hybrid multi-resolution detection of moving targets in infrared imagery

A hybrid moving target detection approach in multi-resolution framework for thermal infrared imagery is presented. Background subtraction and optical flow methods are widely used to detect moving targets. However, each method has some pros and cons which limits the performance. Conventional background subtraction is affected by dynamic noise and partial extraction of targets. Fast independent component analysis based background subtraction is efficient for target detection in infrared image sequences; however the noise increases for small targets. Well known motion detection method is optical flow. Still the method produces partial detection for low textured images and also computationally expensive due to gradient calculation for each pixel location. The synergistic approach of conventional background subtraction, fast independent component analysis and optical flow methods at different resolutions provide promising detection of targets with reduced time complexity. The dynamic background noise is compensated by the background update. The methodology is validated with benchmark infrared image datasets as well as experimentally generated infrared image sequences of moving targets in the field under various conditions of varying illumination, ambience temperature and the distance of the target from the sensor location. The significant value of F-measure validates the efficiency of the proposed methodology with high confidence of detection and low false alarms.     

基于上/下转换发光的新型比率荧光温度探针

温度的可视化实时监测,一直都是科学研究的重点方向。荧光传感是一种具有高灵敏度、快速响应、可视化等优点的半侵入式测温方法,在生物医药等领域已被广泛应用。然而,传统荧光探针容易受到外界条件波动的影响而产生误差。为解决这一问题,可以采用两组荧光检测信号构建比率型荧光探针,通过两组信号的相互校准提高检测的准确性。传统的比率荧光温度探针大多基于下转换荧光发射,这类探针通常由短波长光激发,对生物组织穿透性差且有一定伤害,还会受到生物组织自发荧光的干扰。频率上转换是由长波长激发,短波长发射的一种光致发光现象,由其构建的荧光探针可以克服传统下转换荧光探针的上述缺点。而基于三线态-三线态湮灭(TTA)机理的频率上转换发光体系,由光敏剂和湮灭剂的双分子体系共同构成,因而自身就同时具有上/下转换的发光特性,满足了构建比率型荧光探针的条件。然而目前,基于TTA上转换体系的比率型荧光温度探针还鲜见报导,已报导的工作中仍需要另外添加参比探针。仅通过TTA双分子体系构建的上/下转换比率型荧光温度探针仍然是一大挑战。本文通过将传统的TTA上转换体系(PdOEP/DPA)负载于由温敏型两亲性聚合物Pluronic-F127组装形成的胶束中,形成上转换纳米胶束温度探针。随着温度的升高,聚合物亲水链段水溶性下降,向胶束核心位置收缩,导致负载上转换分子的胶束内部空间体积减小,TTA分子间碰撞概率增大,上转换效率提高,上转换发光的强度也随之提高;与此同时,光敏剂的下转换磷光发射也会发生小幅度的下降。由此上/下转换两组荧光信号构成的比率荧光,可成功实现25~60 ℃范围内对温度的线性检测,并可通过肉眼观察到体系发光由紫红色向蓝紫色的转变,检测结果的重复性良好。TTA上转换分子通过被温敏聚合物胶束的包覆,既解决了在实际应用中探针水溶性差,以及上转换发光易被氧气淬灭的问题,还为上转换体系提供了温敏性质,实现了上转换发光对温度的精确响应。这种基于上转换纳米胶束的比率型荧光温度探针不仅制备方法简单,具有良好的生物相容性,且检测灵敏度高,可以人眼识别,无需外加参比,对生物体内温度在线监测的实现具有重要意义。     

Thermal noise in Hg0.795Cd0.205Te detectors for large biasing fields

Thermal noise in Hg_0.795Cd_0.205Te detectors is estimated for large biasing fields at a lattice temperature of 77 K, by computing the correlation functions of the velocity fluctuations with the Monte Carlo technique. The noise temperature for current components transverse to the field is almost independent of the field, but that corresponding to the parallel component increases by a factor of about 1.3 at 50 V/cm and by a factor of 3.0 at 300V/cm. The thermal noise voltage for a detector of 85 resistance increases from 0.6nV/Hz^1/2 at low biasing fields to about 3nV/Hz^1/2 at a field of 300 V/cm. The noise power is also found to remain constant up to about 75 GHz, and it decreases thereafter by a factor of 0.25 for doubling of the frequency.     

Biolabeling with nanoparticles based on Y2O3: Nd and luminescence detection in the near-infrared

Neodymium based fluorescence presents several advantages in comparison to conventional rare earth or enzyme-substrate based fluorescence emitting sources (e.g.Tb, HRP) . Based on this fact we have herein explored a Nd-based fluoroimmunoassay. We efficiently detected the presence of an oxidized low-density lipoprotein (oxLDL) in human plasma a well-known marker for cardiovascular diseases, which causes around 30% of deaths worldwide. Conventional fluoroimmunoassay uses time-resolved luminescence techniques, with detection in the visible range, to eliminate the fluorescence background from the biological specimens. By using an immunoassay based on functionalized Y₂O₃:Nd³⁺ nanoparticles, where the excitation and emission processes in the Nd³⁺ ion occur in the near-infrared (NIR) region, we have succeeded in eliminating the interferences from the biological fluorescence background, avoiding the use of time-resolved techniques. This yields higher emission intensity from the Nd³⁺-nanolabels and efficient detection of anti-oxidized low-density lipoproteins (anti-oxLDL) by Y₂O₃:Nd³⁺-antibody-antigen conjugation, leading to a novel biolabeling method.