A Self-Diffraction Temporal Filter for Contrast Enhancement in Femtosecond Ultra-High Intensity Laser

We demonstrated a nonlinear temporal filter based on the self-diffraction(SD) process. Temporal contrast enhancement, angular dispersion and spectrum broadening properties of the SD process are investigated in experiment and simulation. Driven by spectral phase well compensated laser pulses with bandwidth of 28 nm,the filter produced clean pulses with a temporal contrast higher than 1010 and excellent spatial profile, the spectrum of which was smoothed and broadened to 64 nm. After implementing this filter into a home-made30 TW Ti:sapphire amplifier, temporal contrast of the amplified pulses was enhanced to 1010 within the time scale of-400 ps.     

A High-Efficiency MRI Contrast Agent as well as a Tumor Therapeutic Agent

Inorganic/polymercore/shell nanoparticles (NPs) for theranostics have always attracted research interest due to their flexible composition and facile synthesis. Here, core/shell NPs are prepared with gadolinium hydroxide nanorods cores and Mn ion-doped polydopamine shells. After PEG modification, the relaxation rate of Gd(OH)₃@MnPDA-PEG NRs achieved 35 s⁻¹mm ⁻¹. The characterization results indicate that the predoping Mn ions obviously promote the effect of MRI compared with the nanorods without or with postdoping Mn ions, and the predoping method can effectively control the actual doping account of metal ions. Considering the toxicity, dopamine and manganese in molar ratio of 8:1 is finally chosen. Gd(OH)₃@MnPDA-PEG nanorods are conducted in vivo and in vitro imaging and therapeutic experiments. The results show that the nanorods has low biological toxicity, excellent magnetic resonance imaging effects, clear photoacoustic imaging, and photothermal therapy effects.     

Intensity Correlation Function of a Single-Mode Laser Driven by Colored Cross-Correlation Noises in Modulation of a Bias Signal

By using the linear approximation method, the intensity correlation function is calculated for a single-mode laser modulated by a bias signal and driven by colored pump and quantum noises with colored cross-correlation. We found that, when the correlation time between the two noises is very short, the behavior of the intensity correlation function versus the time, in addition to decreasing monotonously, also exhibits several cases, such as one maximum, one minimum, and two extrema. When the correlation time between the two noises is very long, the behavior of the intensity correlation function exhibits oscillation and the envelope is similar to the case of short cross-correlation time.     

近共心腔气体拉曼光谱增强方法研究

对海水中溶存气体(甲烷、二氧化碳等)的探测是海洋环境监测和资源探测的重要环节,由于拉曼光谱技术可实现多组分同时探测的优势,被视为发展海洋溶存气体探测技术的首选,而探测灵敏度的提高则是推动该项技术实用化的关键。针对提高拉曼光谱气体探测灵敏度这一问题,设计并搭建了一套基于近共心腔拉曼信号增强系统,开展了信号收集方向和激发光多次散射模式对信号强度和信噪比影响的研究。研究发现,信号收集方向与腔镜光轴之间的夹角越小,所收集的信号越强、信噪比越大,当夹角为30度时,信噪比是垂直方向的16倍;近共心腔直线型多次反射模式,与共心腔模式相比信噪比增强了近三倍。采用最优化实验条件,该系统与常规拉曼系统相比,信号强度和信噪比增强效果均在70倍左右。根据该系统对空气中CO₂的相应强度(空气中CO₂的浓度为0.648 mg·L-1),以三倍于噪声强度计算检测限,估算出该系统对CO₂的探测灵敏度约为0.19 mg·L-1,依据CO₂与CH₄拉曼散射截面比为1/6,估算该系统对甲烷的检测限约为11.5 μg·L-1。     

High-Stability High-Energy Picosecond Optical Parametric Chirped Pulse Amplifier as a Preamplifier in Nd:Glass Petawatt System for Contrast Enhancement

We demonstrate a novel picosecond optical parametric preamplification to generate high-stability, high-energy and high-contrast seed pulses. The 5 ps seed pulse is amplified from 60 pJ to 300μJ with an 8.6 ps/3 mJ pump laser in a signal stage of short pulse non-collinear optical parametric chirped pulse amplification. The total gain is more than 10~6 and the rms energy stability is under 1.35%. The contrast ratio is higher than 10~8 within a scale of 20 ps before the main pulse. Consequently, the improvement factor of the signal contrast is approximately equal to the gain 10~6 outside the pump window.     

光折变介质的相位共轭波强度的近似表达式

以光折变介质中非线性耦合波微分方程的一种精确解为基础，对在推导这种精确解过程中起重要作用的一个守恒量进行讨论，通过初等变换，在不同的特殊条件下得到相位共轭波强度的几处近似表达式。与报道的其它近似方法相比，本近似方法不需要建立及求解简化的微分方程因而具有普适，简单的特点。     

基于空芯光纤增强拉曼光谱气体探测方法研究

拉曼光谱技术具有多组分同时探测、分析周期短和非接触等特点,被应用于多个领域,但是由于较低的探测灵敏度,限制了拉曼光谱技术的发展。针对提高拉曼光谱技术对气体探测灵敏度问题,本文设计并搭建了一套基于空芯光纤气体拉曼光谱增强系统,开展了空芯光纤拉曼光谱系统和后向散射拉曼光谱实验系统对比实验研究。实验结果表明,空芯光纤对信号、背景和噪声都具有放大效果,以空气中氮气和氧气为探测物质,与后向拉曼光谱信号相比,在相同探测时间情况下,信号强度增强60倍以上,信噪比增强约6倍;在相同探测强度情况下,探测时间仅为后向散射的1/60,噪声为后向散射拉曼系统的1/2。     

Magnetic Field Enhancement of the Optogalvanic Signal in a Hollow Cathode Discharge

An optogalvanic signal enhancement was obtained in a magnetic field applied on a hollow cathode discharge-detector. In this magnetic field a mutual correlation was observed between optogalvanic signal behaviour, discharge current change and lower level population of the transition corresponding to the 632,8 nm laser irradiation spectral line.     

一种实用的可见光图像自适应对比度增强方法

提出了一种基于图像一阶、二阶统计特性的自适应可见光图像对比度增强方法。通过分析可见光图像数字特性,提取了图像序列两个时间平稳的特征,即均值和方差。以此为基础,在灰度域对图像进行对比度增强。实验结果表明,提出的方法有效地增强了图像的对比度,同时抑制了部分起伏的背景。该算法在视觉质量上优于传统的基于图像最大最小值的对比度增强方法和直方图均衡方法,而且易于实现。     

Size Distribution of Magnetic Cores in Contrast Materials for MRI Diagnostics

In medical diagnostics by magnetic resonance imaging (MRI) one uses contrast materials to enhance preferred tissues. These materials generally contain cores of small magnetic particles of iron compounds. Their size distribution affects their tissue preference. We have used Mössbauer spectroscopy to determine the particle size distribution of six different contrast materials. The spectra of the materials at temperatures 4.6 K to 260 K were analyzed in terms of a particle distribution where the volume determines the super-paramagnetic relaxation rate and the Fe magnetic hyperfine field. The average particle size obtained agrees with determinations by other experimental techniques.     

ITO导电薄膜透明图案对比度增强方法

铟锡氧化物(Indium Tin Oxide,ITO)导电层是触控显示技术的绝对定位元件,为保障定位的灵敏性和准确性,需对导电层表面缺陷进行质量检测.本文针对导电层透明区域机器视觉自动检测存在的问题,提出了图案对比度增强的方法.该方法首先利用ITO材料的光谱属性及其表面光学特性,设计出用于ITO导电层检测的近红外同轴光照明,将图像对比度从零提高到4.5%.在通过光学方法实现了对比度从无到有的转变后,充分利用数字图像预处理的优势,结合基于小波变换的非线性增强方法,最终成功将对比度提高至16%,为后续ITO导电层缺陷的分析和识别提供了良好保障.     

周期信号调制色泵噪音驱动下单模激光光强关联函数的时间演化特性

采用周期信号调制色泵噪音驱动的单模激光模型,运用线性化近似方法研究了单模激光系统光强关联函数C(t)随时间的演化关系,分析了调制信号的振幅B、频率Ω等对光强关联函数随时间演化的影响. 发现在泵噪音自关联时间τ>>1的情形下,随着调制信号频率Ω、振幅B的增加,C(t)随时间的演化为单调衰减;在τ>>1的情形下,随着调制信号频率Ω、振幅B的增加,C(t)随时间的演化均为周期性振荡衰减.     

周期信号调制色泵噪音驱动下单模激光光强关联函数的时间演化特性

采用周期信号调制色泵噪音驱动的单模激光模型,运用线性化近似方法研究了单模激光系统光强关联函数C(t)随时间的演化关系,分析了调制信号的振幅B、频率Ω等对光强关联函数随时间演化的影响.发现在泵噪音自关联时间τ<<1的情形下,随着调制信号频率Ω、振幅B的增加,C(t)随时间的演化为单调衰减;在τ>>1的情形下,随着调制信号频率Ω、振幅B的增加,C(t)随时间的演化均为周期性振荡衰减.     

对一种新的基于局部标准差的自适应对比度增强算法的评价

介绍一种基于图像局部标准差变换的自适应增强算法通过将图像的局部标准差映射为高斯函数得到一个非线性对比度增益函数,使图像的细节区域得到较大幅度的增强,同时抑制平滑区域的噪声以及发生于陡峭边缘的“振铃伪迹”(Ringing Artifact)通过不同类型的图像以及对比度-噪声比(Contrast-to-Noise Ratio)演示了算法的性能,并与几种常用的图像增强方法进行了比较结果表明该算法对于低对比度的图像细节具有较好的增强效果,同时能够避免平滑区域噪声的过度增强及陡峭边缘的振铃伪迹.     

Algorithm for Determining the Coordinates of a Hydroacoustic Source Using the Correlation Function of Its Signal

Acoustical Physics - Abstract—An algorithm for determining the coordinates (distance and depth) of a broadband signal source has been developed, which uses as the input data the parameters of...     

基于信号增强的电化学发光适配体传感器检测三磷酸腺苷

基于三磷酸腺苷(ATP)适配体与ATP分子作用后可以显著增强电化学发光信号的性能,研究了一种用于ATP含量检测的电化学发光适配体(ECL-aptamer)传感器。通过电沉积方法获得纳米金电极。3′端标记联吡啶钌发光分子的探针DNA通过5′端修饰的巯基自组装到纳米金电极表面,然后与5′端标记二茂铁分子的ATP核酸适配体互补杂交,形成刚性线形的双链DNA,由此构建的传感器产生较弱的电化学发光(ECL)信号。该传感器在ATP溶液中孵化后,由于ATP分子与ATP适配体强的特异性结合,使得适配体分子与探针DNA分子解离,从电极表面脱落进入溶液,此时电极表面的探针DNA在强电解质溶液中可以形成发卡型的茎环结构,产生显著增强的ECL信号。ECL信号强度与ATP浓度的对数值呈线性关系,线性范围为10.0～1.0×10⁵ pmol/L,相关系数r=0.995 9,检测限为5.0 pmol/L。该传感器的灵敏度与检测范围高于目前已报道的结果,显示出了ATP检测的应用潜力。     

交叉关联程度受时间周期调制情况下的单模激光光强关联函数

采用线性化近似方法计算了单模激光系统的光强关联函数,讨论了光强关联函数随时间的演化关系,发现光强关联函数呈现周期振荡的现象.关联函数振荡的幅度和周期不受量子噪音强度、抽运噪音强度和交叉关联程度的影响,输入信号频率会改变关联函数振荡的周期和幅度,但不改变振荡的平衡位置,量子噪音强度会改变振荡极值的位置,四个参量都改变关联函数衰减的初始值,但关联函数对时间周期调制频率不敏感.