光纤式微液滴光学检测与计数单元仿真分析

为实现微流控芯片上微液滴的检测与计数，设计了光纤式检测与计数单元，使用TracePro软件进行建模仿真以便为检测信号处理提供依据。根据液滴通过检测区域时引起的光强变化来实现计数，分析了照明光束准直性、液滴尺寸、液滴相对溶液折射率以及接收光纤相距芯片距离对光强变化的影响。仿真实验结果表明，照明光束准直性越差，液滴半径越大，相对溶液折射率越低，接收光纤距离越近，相对光强变化越明显，并且液滴大小决定着光强变化曲线中是否会出现双波谷现象，液滴半径小于13 μm时，液滴检测信号为明显的单波谷，半径大于17 μm时，液滴信号为明显双波谷。根据仿真结果提出了检测信号的处理方法，表明该单元可以实现微流控芯片上微液滴的检测与计数功能。     

流动聚焦微通道中双重乳液乳化行为研究

本文基于VOF(Volume of Fluid)相界面追踪方法,建立了流动聚焦微通道中双乳液液滴形成的模型,研究了互不相溶的三种流体在微流控系统中形成双重液滴的典型物理过程,给出了双重液滴形成的典型工况,分析了流动参数和工质物性对液滴形成过程的影响。结果表明:双重乳液液滴形成过程可分为滴式与喷式两种模式;外流体流量增大时液滴形成模式由滴式转变为喷式,所形成的双重液滴尺寸减小;中间流体流量变化对液滴形成模式、所形成的双重乳液内液滴尺寸影响不明显,外液滴随中间流体流量增大而增大。     

T型微通道中液滴半阻塞不对称分裂行为研究

液滴不对称分裂是获得不同尺寸微液滴的优选方法,研究液滴不对称分裂行为对于生物医学、能源化工及食品工程等领域具有重要意义.本文研制T型微通道芯片并设计搭建T型微通道液滴半阻塞不对称分裂行为可视化实验平台,研究流量调控对微液滴分裂比的影响规律,并建立理论模型对分裂比进行预测,得到以下结论:液滴不对称挤压分裂过程分为挤压前期、挤压后期和快速夹断阶段,在挤压前期,液滴颈部宽度随时间呈线性变化,在挤压后期,颈部宽度随时间呈指数关系,而在快速夹断阶段,液滴颈部向心收缩的界面附加压力占主导,液滴颈部宽度剧烈收缩,呈断崖式减小;调控分支通道流量可对液滴不对称分裂比进行调控,且调控作用受毛细数影响较大;基于液液流动压降模型的液滴分裂比预测模型能够有效预测液滴分裂比.     

制备复合液滴的微尺度流动方法

微尺度流动能够一步到位地制备不同结构和功能、尺寸在微米量级的复合液滴.文章回顾了几种常见的基于复合液滴的微尺度流动方法,包括同轴电雾化、复合流动聚焦、微流控芯片、玻璃微毛细管等,并对各种技术的原理和进展进行了简要概括和分析.在这类流动中,不同种类的流体在一定的几何结构通道或外力场作用下平稳地拉伸成微细射流并最终破碎成复合液滴.在同轴电雾化和复合流动聚焦技术中,从毛细管流出的流体能够形成稳定的锥-射流结构,当外力作用改变时能够形成不同的流动模式.在微流控芯片和玻璃微毛细管技术中,流体被约束在固定管道内,不同管道构型下能够形成不同的流动形态.这些方法都采用纯物理机理,过程稳定、易于操作,制备的复合液滴粒径可控,单分散性好,微观结构可设计,在科学研究和工程实际中具有重要的应用价值.      

介质阻挡放电中单双层气隙内微放电通道的等离子体参量研究

采用H型放电间隙的介质阻挡放电装置,在氩气和空气的混合气体中,得到了三种新颖的等离子体发光斑图。较于传统获得的斑图,这三种发光斑图是产生在单层气隙与双层气隙结合的气隙装置之中。通过相机拍摄到的斑图照片,可以发现单层气隙和双层气隙中微放电通道呈现的发光亮度、颜色、放电面积等状态有所不同,这表明微放电通道所处的等离子体状态可能各不相同。通过分析这三种等离子体发光斑图, 利用发射光谱法首次研究了单层气隙和双层气隙内微放电通道的等离子体参量。实验通过采集氮分子第二正带系(C3Π_u→B3Π_g)的发射谱线计算了单层气隙和双层气隙内微放电丝的分子振动温度,并进一步利用氩原子696.57 nm(2P₂→1S₅)谱线的展宽分析了单层气隙和双层气隙内微放电丝的电子密度。结果发现： 在左右相同厚度的双层气隙中,耦合微放电丝的分子振动温度基本相同,电子密度也趋于一致,单层气隙内微放电丝的分子振动温度要高于双层气隙内微放电丝,电子密度则小于双层气隙内微放电丝。单层气隙和双层气隙中不同微放电通道等离子体状态的差异性使之形成多种折射率的等离子体光子晶体,其周期性排布将具有更加丰富的带隙结构。     

基于双波长像面数字全息显微的微通道检测

针对微流控芯片通道三维形貌的可视化测量需求,搭建了一套反射式离轴双波长像面数字全息显微测量系统。首先,利用分辨率靶和标准样片对系统的横向、纵向分辨率和放大倍数进行标定实验,结果表明双波长全息显微系统在横向宽度及纵向深度测量中具有较好的准确性和可行性。然后,利用该系统分别对由PDMS材料制成的直通道、圆形小室结构微流控芯片以及硅基底微流控芯片通道进行三维形貌检测,并得到定量结果：直通道结构深度为48.6μm,宽度为75.8μm;圆形小室微通道深度为48.5μm,宽度为76.6μm;硅基底微流控芯片测量得到通道深度为61.6μm。上述结果与白光干涉仪的测量结果具有良好的一致性,说明双波长全息显微系统具有较高的可靠性和准确性,可为微流控芯片微通道检测提供新的成像检测方法。     

用于微流控液滴检测的共焦激光诱导荧光检测系统

以发射波长为473nm的二极管泵浦激光器为激发光源,搭建适于微流控液滴检测的共聚焦激光诱导荧光检测系统.系统玻璃芯片采用简易加工技术加工而成.并用2%十八烷基三氯硅烷将微通道处理为具有强疏水性质.荧光素钠溶液在T形通道交叉处被十四烷剪切形成液滴,液滴流经检测点时被激光诱导荧光系统检测.荧光素钠的检出限为1.1×10<'...     

微流控制备单分散微米级SiO2微球

采用软模板法制备出了聚二甲基硅氧烷微流控装置。利用该装置讨论了正硅酸乙酯和氨水的用量分别对反应体系凝胶化时间的影响,确定了制备SiO2微球的优化反应体系,即二甲基乙酰胺、正硅酸乙酯和氨水的体积比为8∶4∶1,实验所需的反应温度为60 ℃。实验发现:在微流体通道中,分散相的流速越大,粒径越大;连续相流速越大,粒径越小。因此,通过控制微流控装置中分散相和连续相的流速制备了粒径40~220 m的单分散SiO2微球,并对其形貌进行表征。光学显微镜和粒径分析均表明所制备的SiO2微球球形度高,单分散性好。     

溶液液滴蒸发变干的环状沉积

液体蒸发驱动的颗粒自组装现象在许多的工业技术中有重要应用. 本文利用显微镜观测含有颗粒物质的液滴变干后留在固体表面的颗粒形成的环状沉积图案. 采用微米粒径的SiO₂小球水溶液液滴蒸发变干模拟咖啡环的形成过程, 结果发现液滴蒸发过程中接触线的钉扎是环状沉积的必要条件. 在液滴蒸发过程中颗粒随着补偿流不断的向液滴边缘移动, 聚集在接触线处形成环. 液滴蒸发变干后残留在液滴内部的颗粒数随颗粒质量分数的增加而增加, 可以达到单层的颗粒排列. 而玻璃衬底上的颗粒环在颗粒质量分数很小时, 形成单层排列, 且一排一排地生长. 蒸发过程中颗粒环由于液滴边缘的尺寸限制向液滴中心缓慢移动. 这会导致液滴中不同大小颗粒的分离. 关键词： 液滴 接触线 蒸发 颗粒     

微通道内不混溶气液两相二氧化碳界面动力学行为的格子Boltzmann研究

将高精度的二氧化碳状态方程与气液两相流格子Boltzmann方法中的伪势模型耦合,研究微通道内二氧化碳气液两相流动的界面动力学行为,包括二氧化碳气泡和液滴的分裂、合并、变形,以及气液两相二氧化碳在演化过程中的质量交换.研究发现：当分裂和合并行为达到平衡,并且两相之间不发生质量交换时流动达到稳态.稳态时的流型主要依赖于表面张力,惯性力,管道的润湿性,以及初始体积分数.当表面张力较大时,微通道内形成的二氧化碳气泡或液滴会收缩成圆形,此时二氧化碳气泡或液滴会堵塞微通道,形成段塞流;随着表面张力的减小,形成的气泡或液滴不容易收缩,在微通道内更容易发生变形,出现泡状流或环状流.当壁面润湿性为强疏水性时,二氧化碳在微通道中的流动为环状流,其它润湿性下,流型为段塞流.体积分数较小时,二氧化碳两相流动的流型为段塞流,体积分数较大时,流型为环状流.     

Theoretical analysis and simulation of conjugate heights for dual-conjugate AO system in lidar

A multi-conjugate adaptive optics （MCAO） can offer a possibility of widening field of view （FOV） characterized by the isoplanatic angle, and the choose of conjugate height becomes a basic problem for MCAO, which influences the size of iosplanatic angle. Considering the application of lidar, the isoplanatic angle＇s expressions of two deformable mirrors （DMs） MCAO for uplink and downlink are deduced. The effects of conjugate heights for dual-conjugate AO are thoughtfully discussed, and the isoplanatic angles are further analyzed. The results show that the isopanatic angle varies with the conjugate height and reaches the maximum as the conjugate height is at the optimal altitude. Moreover, the optimal conjugate height changes with the propagation distance.     

Quick single-photon detector with many avalanche photo diodes working on the time division

Due to the limit of response speed of the present single-photon detector, the code rate is still too low to come into practical use for the present quantum key distribution (QKD) system.A new idea is put up to design a quick single-photon detector.This quick single-photon detector is composed of a multi-port optic-fiber splitter and many avalanche photo diodes (APDs).Au of the ports with APDs work on the time division and cooperate with a logic discriminating and deciding unit driven by the clock signal.The operation frequency lies on the number N of ports, and can reach N times of the conventional single-photon detector.The single-photon prompt detection can come true for high repetition-rate pulses.The applying of this detector will largely raise the code rate of the QKD, and boost the commercial use.     

Characterization of PolyA and PolyC mismatches by Raman spectroscopy

A.C mismatches are studied by Raman spectral characterization of PolyA, PolyC, and their equimolar complex in solution of 0.14 mol/L Na ,pH7.0.Experimental results show that A·C mismatches occur to be A/B (mainly A) conformers, and unlike Watson-Crick base pairing, this kind of mismatches is stabilized by only one hydrogen bond involving cytosine N4H2 and adenine N7.The formation of A·C complex makes the base stacking interactions much stronger, and conformation of the backbone more ordered, which leads to obvious Raman hypochromic effect with some shifts in corresponding bands.     

Improvement of four-wave mixing-based wavelength conversion efficiency in dispersion shifted fiber by 40-GHz clock pumping

40-GHz clock modulated signal as a pump to improve the efficiency of four-wave mixing (FWM)-based wavelength conversion in a 26.5-km dispersion shifted fiber (DSF) is investigated. The experimental results demonstrate that the conjugated FWM component has higher intensity with the clock pumping than that with the continuous-wave (CW) light pumping. The improvement of FWM-based wavelength conversion efficiency is negligible when the pump power is less than Brillouin threshold. But when the pump power is greater than Brillouin threshold, the improvement becomes significant and increases with the increment of pump power. The improvement can increase up to 9 dB if pump power reaches 17 dBm.     

Multi-pulse operation of a Kerr-lens mode-locked femtosecond laser

Our experimental results show that the presence of a proper amount of negative group velocity dispersion is essential to multi-pulse operation of a Kerr-lens mode-locked femtosecond laser. We demonstrate that the pulse separations and the number of pulses contained within a cavity round trip are strongly dependent on the initial perturbations. The results allow us to get a better understanding on the influences of the convoluted self-phase modulation and intra-cavity dispersions on the stable multi-pulse oscillation in a Kerr-lens mode-locked femtosecond laser.     

Propagation of Helmholtz-Gauss beams in weak turbulent atmosphere

Based on the Rytov approximation of light propagation in weak turbulent atmosphere,the closed-form expressions of field and average irradiance of each one of the four fundamental families of Helmholtz-Gauss (HzG)beams:cosine-Gauss beams,stationary Mathieu-Gauss beams,stationary parabolic-Gauss beams,and Bessel-Gauss beams,which are propagating in weak turbulent atmosphere,are obtained.The results show that the field and average irradiance can be written as the product of four factors:complex amplitude depending on the z-coordinate only,a Ganssian beam.a factor of complex phase perturbation induced by atmospheric turbulence,and a complex scaled version of the transverse shape of the non-diffracting beam.The effect of weak atmospheric turbulence on irradiance distribution of the HzG beam can be ignored.     

An effective method for reducing speckle noise in digital holography

An effective method for reducing the speckle noise in digital holography is proposed in this paper.Different from the methods based on classical filtering technique,it utilizes the multiple holograms which are generated by rotating the illuminating light continuously.The intensity images reconstructed by a series of holograms generated by rotating the illuminating light possess different speckle patterns.Hence by properly averaging the reconstructed intensity fields,the speckle noises can be reduced greatly.Experimental results show that the proposed method is simple and effective to reduce speckle noise in digital holography.     

Influence of purity of HfO2 on reflectance of ultraviolet multilayer

The impurities in two kinds of HfO2 materials and in their corresponding single layer thin films were determined through glow discharge mass spectrum technology and secondary ion mass spectrometry(SIMS) equipment respectively.It was found that ZrO2 was the main impurity in the two kinds of HfO2 either in the original HfO2 materials or in the electron beam deposited films.In addition,the difference of Zr content in the two kinds of HfO2 single laver films was much laxger than that of the other impurities such as Ti and Fe.which showed that it was just ZrO2 that made the difference between the optical performance of the film products including the two kinds of HfO2.With these two kinds of HfO2 and the same kind of SiO2.we deposited HfO2/SiO2 multilayer reflective coatings at the wavelength of 266 nm.Experimental results showed that the reflectances of these two mirrors were about 99.85% and 99.15% respectively,which agreed well with the designed results what were based on the optical constants obtained from the corresponding single layer thin films.     

Speech enhancement by array crosstalk resistant ANC and spectrum subtraction

Microphone array-based speech enhancement has great importance for speech communications and speech recognition. To reduce the aperture of the microphone array and to increase the effect of the speech enhancement will greatly broaden the application areas of the microphone array. An array crosstalk resistant adaptive noise cancellation method is therefore presented. And then an improved spectral subtraction algorithm is further cascaded to obtain better enhancement results. Theoretic analysis and experiments indicate that the proposed scheme needs only a very small microphone array while it simultaneously achieves a higher SNR improvement. Besides, the proposed scheme can be used in many noisy environments and is easy for real-time implementation.