超纯水中杂质对光子相关谱法测量纳米颗粒粒径的影响

为了研究光子相关光谱法测粒技术中,溶液介质中的杂质对纳米颗粒有效直径和分散度测量准确性的影响,获取并分析了3种超纯水蒸发后残留杂质的显微图像,讨论了上述3种水对标称直径为960、340、90、60nm的颗粒物测定结果的影响。研究结果表明,水中杂质会增大光子平均计数率,以及增大100nm以下单分散颗粒的有效直径和分散度的测量结果;对于自身分散度较大的颗粒,水质对分散度测量结果的影响不明显。     

光子相关光谱法纳米颗粒测定的准确性问题

本文基于光子相关光谱法测粒原理,系统研究了影响该法测定纳米颗粒物有效直径和分散度的准确性的因素,包括如何配置实验系统及实验参数、信号获取中的干扰、使用的分散介质含杂质颗粒物的干扰以及数据处理中的基线选择等对测量结果的影响。本文通过多角度测量分析了测量装置的界面反射对cps值的影响,分析了噪声的来源和噪声对测量结果的影响。通过对纳米金及二氧化硅颗粒的测定,验证了信号接收角度和分散溶液介质的性质对测量结果的影响,指出选择不同基线的方法和采用噪声剔除技术,可减少或消除噪声的影响。     

基于光子计数调制的光学时域反射测量

针对光学时域反射测量的信噪比受到光子计数的量子起伏的影响,本文提出了光子计数调制技术应用于1.55μm单光子探测光时域反射测量系统,该方法根据相干光场量子涨落的噪声功率在频域上具有均匀分布的特性,采用光子计数调制与锁相放大器解调的方法抑制了量子起伏.实验结果表明,通过改变锁相放大器的积分时间设置滤波带宽,改善了光子计数的信噪比.与光子计数直接测量的结果相比,光子计数调制的光学时域反射测量的信噪改善比达到28.3 dB.     

自动基线拟合累积量算法纳米颗粒反演

传统累积量反演算法是一种经典的纳米颗粒反演算法,但是利用传统累积量算法对颗粒粒径进行计算时基线值的不同会影响颗粒粒径信息.提出采用一种自动基线拟合的累积量算法,此方法利用光子相关光谱函数作为目标函数进行反演,直接拟合基线值及颗粒粒径信息.利用光子相关光谱实验台对90 nm的乳胶颗粒进行了测试并采用以上两种累积量算法进行数据处理,实验结果表明采用传统累计量算法,由于基线值的不同和噪声的影响,其结果受相关时间影响较大,而采用本文自动基线拟合累积量方法,其测量结果其稳定性好,基本不受相关时间影响.     

光阻积分式颗粒粒度测试方法的模拟研究

对传统光阻式颗粒计数器的计数方法进行了改进 ,采用积分统计的方法进行颗粒计数 ,研究了信号阀值的选取 ,以及信号噪声和颗粒脉冲信号的重叠对粒度分布求解的影响。数值模拟表明 ,在整个粒经范围内 ,求解结果对噪声不敏感 ,颗粒信号重叠程度加大 ,粒度求解结果在测量范围的上限的偏差加大 ,但对于中部和下限的粒度重合程度非常好。     

紫外荧光大气SO2浓度监测系统

大气污染物SO_2分子在紫外光的作用下会激发出一定波长的荧光,由此开发出一种大气SO_2浓度监测系统。整个系统由光路、电路和气路三部分构成,光电倍增管将探测到的荧光信号转换为电脉冲信号,经过电路处理后,由光子计数板计数,通过虚拟仪器平台实现系统的测控。该方法克服了化学方法测量时需要试剂、采集时间长等缺点。实验结果表明,系统实现了激发光213.8nm和荧光峰值320nm的最佳光谱匹配,当累积时间为300s时,监测极限为0.5ppb,重复精度可达±1.5%。     

EUV波段光子计数成像探测器信息处理器的设计与实现

EUV波段光子计数成像探测器通过对30.4nm的He+共振散射分布进行成像,从而对地球等离子体层的分布进行研究。信息处理器是EUV波段光子计数成像探测器的核心部分,利用FPGA进行信息处理器的设计,从而完成对图像信号的放大、整形、保持、量化、采集和传输等重要功能控制,空间分辨率达到0.28mm。     

立包包装机出口烟条缺包检测装置的设计

目的 为了解决立包包装机不能有效检测和自动剔除烟条缺包不合格产品的问题。方法 设计一套基于光子检测的烟条缺包检测装置,通过对X射线管、高压电源、X射线探测器、主控板、显示屏、缺包烟条剔除机构、OPA354和AMP02降增益二级放大、高斯滤波处理、检测移位程序的设计等,实现立包包装机产生的缺包烟条不合格产品的全部检测并准确剔除。结果 该光子条缺包检测装置安装后,其缺包烟条检出剔除率≥99.9%,误剔率≤0.01%。结论 该光子条缺包检测装置能提升产品质量、降低物耗、提高设备作业率、降低缺包烟条进入下道工序的风险,可推广应用于行业内所有包装机组设备上。     

光子图象统计处理的计算机模拟

用统计理论分析了光子图象中信号和噪声的分布，提出了用Ｘ２准则拟合信号和背影的强度及分布区域，并统计区域中计数是背影的概率大于是信号的概率的计数去除。     

多功能超高速计数器

脉冲信号计数是最简单的数据获取工作和最基本的测量方法。在许许多多高科技领域中,对计数器(Counter)计数分辩率提出很高要求。当前,核物理上应用的计数器都有计数率较高(最高为200MHz),结构复杂,价格昂贵的缺点。本文报导我们最新研制的一种计数率为500MHz的超高速计数器,后级采用Intersil公司生产的通用计数器电路ICM7216B,只需外接少量元件就可构成最简单多功能超高速计数系统。     

NP1024神经网络处理器中的数据传输与图形显示

介绍在ＮＰ１０２４神经网络系统中如何将网络中有关数据按要求高速送到ＬＣ－ＳＡ屏上的接口及显示电路的软件硬件设计技巧。     

Individual detection of single-nanometer-sized particles in liquid by photothermal microscope

We have developed a thermal lens microscope for liquid-phase and surface microanalyses. By applying the thermal lens microscope to particle detection, we succeeded in detecting a pulsed photothermal signal from single-nanometer-sized particles in liquid and counting them individually. The samples were polystyrene latex particles (190 and 80 nm in diameter) and colloidal Ag particles (10 nm in diameter). To verify that the detected pulsed signals corresponded to the single-particle photothermal effects, we confirmed the items as described below using 190-nm polystyrene particles. First, no pulsed signal was generated under irradiation by either the excitation beam or the probe beam. Second, the pulse counts were proportional to the expectation value of the particles in the detection volume and zero for ultrapure water blank. Third, the pulse counts' distribution in a series of unit times had a Poisson distribution when the expectation value of the sample was much less than 1. Then, we demonstrated counting 80-nm polystyrene particles and 10-nm Ag particles in water. The pulsed signals were clearly distinguished from noise, and the signal-to-noise ratio was as large as 5. Finally, we discussed differences between the conventional thermal lens effect and the single-particle photothermal effect. Individual nanometer-sized particle detection by photothermal effect was the first demonstration.     

一种新的动态光散射纳米颗粒反演算法

由于传统累积量反演算法计算结果随相关时间的变化有较大的波动,提出一种新的累计量算法,此方法直接利用光子相关光谱函数作为目标函数进行反演,减少相关时间选择对测量结果的影响.在介绍传统累积量光子相关光谱法颗粒粒径分布反演算法的基础上,引入以光子相关光谱函数作为累积量算法的目标函数的反演算法,利用实验平台对90 nm的乳胶颗粒进行测量.运用实验获得的相关函数数据研究两种累积量算法和相关时间之间的关系,实验结果表明,采用传统累计量算法其结果受相关时间影响较大,而本文所提算法稳定性好,在较长相关时间范围内基本不受相关时间影响.     

High efficiency single photon detection via frequency up-conversion

Abstract

We propose a method of single photon detection of infrared (IR) photons at potentially higher efficiencies and lower noise than allowed by traditional IR band avalanche photodiodes (APDs). By up-converting the photon from the IR, e.g. 1550 nm, to a visible wavelength in a nonlinear crystal, we can utilize the much higher efficiency of silicon APDs at these wavelengths. We have used a periodically poled lithium niobate (PPLN) crystal and a pulsed 1064 nm Nd:YAG laser to perform the up-conversion to a 631 nm photon. We observed conversion efficiencies as high as ～ 80%, and demonstrated scaling down to the single photon level while maintaining a background of 3 ×s; 10^?4 dark counts per count. We also propose a 2-crystal extension of this scheme, whereby orthogonal polarizations may be up-converted coherently, thus enabling complete quantum state transduction of arbitrary states.     

Chemical synthesis and characterization of amorphous Fe-Ni-B magnetic nanoparticles

We have synthesized Fe-Ni-B amorphous nanoparticles by chemical reduction of the transition metal solution. A compositional study shows that the nominal Ni/Fe ratio is preserved. The new preparation method used yields a much higher boron composition than the one obtained traditionally by rapid quenching and other chemical synthesis previously reported. For all compositions, the size of the particles is about 2.1 nm diameter with a narrow log-normal distribution.     

Discriminator threshold selection logic to improve signal to noise ratio in photon counting

The discriminator threshold plays a vital role in photon counting technique used with low level light detection in lidars and bio-medical instruments. A low discriminator threshold gives high counts due to secondary emitted electrons and ground level (electrical) noise, while high threshold skips the photon pulses having lower amplitude. In both the cases the signal to noise ratio of photon counting system deteriorates. In this article the impact of improper selection of discriminator threshold on photon counting has been described. Here we introduce a simple technique by which the system (micro pulse lidar) selects the discriminator threshold at the set PMT voltage and assigns this value to the multi-channel scaler. The technique is applicable in diverse fields employing photon counting system.     

羟基磷灰石的可控制备及其研究

以CTAB为表面活性剂,利用模板技术水热反应合成了平均粒径为68 nm的近球形颗粒和宽为26～35 nm,长为790～960 nm的纳米羟基磷灰石.通过对合成粉体的X射线衍射、红外光谱和透射电镜分析,探讨了CTAB在水热反应中对羟基磷灰石合成的影响机理.结果表明:通过控制反应温度、pH值、反应时间和CTAB的浓度等工艺条件,可以实现纳米羟基磷灰石粒径大小和形貌的可控生长.     

Influence of electrophoresis waveforms in determining stochastic nanoparticle capture rates and detection sensitivity

Electrophoretic capture and release of charged polystyrene particles at the opening of a membrane pore has been investigated to determine the optimal applied current waveform, iapp(t), for ensuring true stochastic counting rates and to improve detection sensitivity (i.e., Delta(counts per second)/Delta(particle concentration)). In capture and release detection, charged particles are electrophoretically driven to the opening of a small pore ( approximately 60 nm diameter) in a membrane; capture of a single particle at the pore opening at time tau is signaled by a decrease in the flux of a redox species (Fe(CN)(6)4-) through the pore. The captured particle is then released by applying an electrophoretic current in the opposite direction, and the process is repeated to acquire sufficient statistical data to determine the solution particle concentration (Cp) based on the relationship between Cp and the average particle counting rate (tauavg(-1)). Both tauavg(-1) and the method sensitivity are shown, for the detection of 90 nm diameter polystyrene particles, to depend strongly on the applied current waveform. The observed dependence is a consequence of the nonequilibrium distribution of particles in the analyte solution that results from electrostatic forces acting on the particle whenever iapp has a nonzero value. Stochastic capture rates corresponding to an initial uniform distribution of particles are more closely achieved using an applied current waveform that includes an equilibration period (iapp=0) prior to electrophoretic capture. An increase in particle detection sensitivity, relative to the previously reported value, results from this equilibration step.     

Tuning photoresponse through size control of Cu nanoparticles deposited on multi wall carbon nanotubes

In this paper we illustrate a simple method for the production of multiwall carbon nanotubes thin films decorated with copper metal nanoparticles. The structural information obtained from the transmission electron microscopy study performed on samples differing in the quantity of deposited Copper was linked to the opto-electronic properties evaluated with photo-electrochemical measurements. The photo-response evaluated in terms of incident photon-to-charge carrier generation efficiency varied for different sized-Cu-multiwall carbon nanotubes samples across all the visible and near-ultraviolet photon energy range with respect to the response of bare carbon tubes. The photo-response from the sample covered with of 0.5 nm Cu nominal thickness, reached 10.2%, a value 2 times higher than that measured for bare carbon tubes of 5.9%. While this value decreased to 2.8% when the Cu nominal coverage thickened up to 3 nm. The increase in the photo-response found was interpreted as being the result of a remarkable charge transfer between the Cu metal nanoparticles and the carbon atoms in the tube due to the formation of a strong ionic bond at their interface. The results obtained prove that the metal nanoparticle-carbon nanotube composites have optical, electrical and structural properties that can be applied in a variety of nanoscale architectures for novel photo-electrochemical devices.