Effect of the target positions on the rapid identification of aluminum alloys by using filament-induced breakdown spectroscopy combined with machine learning

Filament-induced breakdown spectroscopy(FIBS)combined with machine learning algorithms was used to identify five aluminum alloys.To study the effect of the distance between focusing lens and target surface on the identification accuracy of aluminum alloys,principal component analysis(PCA)combined with support vector machine(SVM)and Knearest neighbor(KNN)was used.The intensity and intensity ratio of fifteen lines of six elements(Fe,Si,Mg,Cu,Zn,and Mn)in the FIBS spectrum were selected.The distances between the focusing lens and the target surface in the pre-filament,filament,and post-filament were 958 mm,976 mm,and 1000 mm,respectively.The source data set was fifteen spectral line intensity ratios,and the cumulative interpretation rates of PC1,PC2,and PC3 were 97.22%,98.17%,and 95.31%,respectively.The first three PCs obtained by PCA were the input variables of SVM and KNN.The identification accuracy of the different positions of focusing lens and target surface was obtained,and the identification accuracy of SVM and KNN in the filament was 100%and 90%,respectively.The source data set of the filament was obtained by PCA for the first three PCs,which were randomly selected as the training set and test set of SVM and KNN in 3:2.The identification accuracy of SVM and KNN was 97.5%and 92.5%,respectively.The research results can provide a reference for the identification of aluminum alloys by FIBS.

Effect of the distance between focusing lens and target surface on quantitative analysis of Mn element in aluminum alloys by using filament-induced breakdown spectroscopy

Ultrafast laser filament-induced breakdown spectroscopy(FIBS)is a potential technique for quantitative analysis of trace elements.In this work,we investigate the effect of the distance between focusing lens and target surface on the FIBS quantitative analysis of Mn element in aluminum alloys,and several major parameters are calculated such as the linear correlation coefficient(R^2),limits of detection(LOD),relative standard deviation(RSD),and root-mean-square error of cross-validations(RMSECV).The results show that the quantitative analysis parameter values before and after filament position are different.The optimal value can be obtained at the filament region,the average values of total 23 positions of R^2,LOD,RSD,and RMAECV were 99.45%,1.41 mg/kg,7.12%,and 0.56%,respectively.Besides,the spatial distributions of quantitative analysis parameter values in filament region are noticeable,and this is essentially due to intensity clamping effect in a filament.

Determination of Melamine by Infrared Spectroscopy Based on Nonlinear Modeling

[Objective] The aim was to develop a nonlinear model of quantitative analysis of melamine content by infrared spectroscopy and provide theoretical basis for the nondestructive detection of melamine. [Method] According to dynamics,mathematical modeling and optimization theory,linear and nonlinear models were respectively set up by taking an absorption peak of 1 550 cm-1 as characteristic absorption peak. [Result] The correlation coefficient of nonlinear model was 0.922 7 and the recovery was 96%,which showed that the nonlinear model was more accurate than linearity model with correlation coefficient of 0.904 9 and recovery of 557%. [Conclusion] It is feasible to determine melamine content by using the nonlinear model quantitatively.

Nonlinear spectroscopy of three-photon excitation of cesium Rydberg atoms in vapor cell

We present nonlinear spectra of four-level ladder cesium atoms employing 6 S1/2→6 P3/2→7 S1/2→30 P3/2 scheme of a room temperature vapor cell.A coupling laser drives Rydberg transition,a dressing laser couples two intermediate levels,and a probe laser optically probes the nonlinear spectra via electromagnetically induced transparency(EIT).Nonlinear spectra are detected as a function of coupling laser frequency.The observed spectra exhibit an enhanced absorption(EA) signal at coupling laser resonance to Rydberg transition and enhanced transmission(ET) signals at detunings to the transition.We define the enhanced absorption(transmission) strength,HEA(HET),and distance between two ET peaks,γET,to describe the spectral feature of the four-level atoms.The enhanced absorption signal HEA is found to have a maximum value when we vary the dressing laser Rabi frequency Ωd,corresponding Rabi frequency is defined as a separatrix point,ΩdSe.The values of ΩdSe and further η=ΩdSe/Ωc are found to depend on the probe and coupling Rabi frequency but not the atomic density.Based on ΩdSe,the spectra can be separated into two regimes,weak and strong dressing ranges,Ωd≤ΩdSe and Ωd≥QdSe,respectively.The spectroscopies display different features at these two regimes.A four-level theoretical model is developed that agrees well with the experimental results in terms of the probe-beam absorption behavior of Rabi frequency-dependent dressed states.

Study of second-order nonlinear hyperpolarisability of all-trans-β-carotene in solutions by linear spectroscopic technique

This paper demonstrates the second-order nonlinear hyperpolarisability γ of all-trans-β-carotene in different solvents by linear spectroscopic technique that is based on resonance Raman scattering and UV-VIS （Ultraviolet-visible） absorption spectroscopy. Owing to the two-level model well describing the link that exists between the resonance Raman scattering and stimulated Raman scattering, the stimulated Raman polarisability αR can be calculated through the two-photon resonance system. The value of γ of all-trans-β-carotene in carbon bisulfide solution is 6.435×10^-33 esu （1 esu of resistance = 8.98755×10^11Ω） that is close to the true value, because the solution of all-trans-β-carotene in carbon bisulfide satisfies the rigid resonance Raman scattering condition. This method is expected to be worthy of applications to measure the second-order nonlinear hyperpolaxisability of a conjugate organic molecule.

光强非线性响应下的光致热弹光谱光强修正

提出了基于光强非线性响应的光致热弹光谱光强修正方法,实现了激光光强的准确修正。控制DFB激光器工作于波长调制模式,设置激光调制频率为16369.75 Hz,通过光纤放大器增强其出射光强非线性项的幅值,光束经多次反射池后汇聚于石英音叉根部激发光热信号,采用数字锁相放大器解调得到对应的谐波信号,通过多项式拟合谐波信号背景,反演得到与浓度及光强分别对应的谐波信号。实验结果表明,当光强从22.03 mW变化至3.16 mW,谐波信号背景幅值与光强具有良好的线性关系,线性相关系数大于0.998,归一化后的谐波信号幅值波动小于0.37%。针对甲烷测量,系统在较大的浓度范围内具有良好的线性响应,谐波信号信噪比表明系统的最低检测限达0.22×10-6。该研究为光致热弹光谱的光强修正提供了一种新的方法,可有效提高LITES系统在长期测量应用中的稳定性。

等离激元调控金纳米孔阵列的超快非线性光学响应

为了明确表面等离激元对金属纳米结构的超快非线性光学响应的调控机制,以金纳米孔阵列为对象,通过电磁场-传热耦合仿真研究不同激发条件下等离激元模式的瞬态光学响应。结果表明,共振激发等离激元模式可以得到比非共振激发更强更快的瞬态光学响应,而且不同等离激元模式诱导产生的瞬态光学响应也存在明显的差异。通过该研究可以为设计高性能全光调控器件提供一种新的思路,并有助于从物理机制上理解表面等离激元共振相关的超快非线性光学效应。

Multi-crack imaging using nonclassical nonlinear acoustic method

Solid materials with cracks exhibit the nonclassical nonlinear acoustical behavior. The micro-defects in solid materials can be detected by nonlinear elastic wave spectroscopy （NEWS） method with a time-reversal （TR） mirror. While defects lie in viscoelastic solid material with different distances from one another, the nonlinear and hysteretic stress-strain relation is established with Preisach-Mayergoyz （PM） model in crack zone. Pulse inversion （PI） and TR methods are used in numerical simulation and defect locations can be determined from images obtained by the maximum value. Since false-positive defects might appear and degrade the imaging when the defects are located quite closely, the maximum value imaging with a time window is introduced to analyze how defects affect each other and how the fake one occurs. Furthermore, NEWS-TR- NEWS method is put forward to improve NEWS-TR scheme, with another forward propagation （NEWS） added to the existing phases （NEWS and TR）. In the added phase, scanner locations are determined by locations of all defects imaged in previous phases, so that whether an imaged defect is real can be deduced. NEWS-TR-NEWS method is proved to be effective to distinguish real defects from the false-positive ones. Moreover, it is also helpful to detect the crack that is weaker than others during imaging procedure.

Multimodal nonlinear imaging of atherosclerotic plaques differentiation of triglyceride and cholesterol deposits

Cardiovascular diseases in general and atherothrombosis as the most common of its individualdisease entities is the leading cause of death in the developed countries.Therefore,visualizationand characterization of inner arterial plaque composition is of vital diagnostic interest,especilly for the early recognition of vulnerable plaques.Established clinical techniques provide valuablemorphological information but cannot deliver information about the chemicai composition ofindividual plaques.Therefore,spectroscopic imaging techniques have recently drawn consider-able attention.Based on the spectroscopic properties of the individual plaque components,as forinstance diferent types of lipids,the composition of atherosclerotic plaques can be analyzedqualitatively as well as quantitatively.Here,we compare the feasibility of multimodal nonlinearimaging combining,two-photon fluorescence(TPF),coherent anti-Stokes Raman scatering(CARS)and second-hamonic generation(SHG)microscopy to contrast composition and mor-phology of lipid deposits against the surrounding matrix of connective tissue with diffractionlimited spatial resolution.In this contribution,the spatial distribution of major constituents of the arterial wall and atherosclerotic plaques like elastin,collagen,triglycerides and cholesterol can be simultaneously visualized by a combination of nonlinear imaging methods,providing a powerful label-free complement to standard histopathological methods with great potential forin vivo application.

Coherent Resonance of Saturated Absorption in Spectroscopy of Counterpropagating Waves

Results of theoretical researches of the saturated absorption resonance shape in a method of the probing field on V-type of transitions are represented. It is shown that in case of opposite circulary polarized optical fields the resonance is shown in the form of cross, and its form strongly depends on relaxation constants of levels and it can be represented as in the form of a dip, and absorption peak. Thus the peak form has exclusively coherent character. Atomic transitions are offered, on which observation of the given effect is possible.

Growth, Crystal Structure and Characterization of a New Single Crystal: Lithium Sodium Acid Phthalate (LiNaP), for Third Order Nonlinear Optical Applications

A new alkali metallo-organic single crystal of Lithium Sodium Acid Phthlate (LiNaP) complex has been synthesized from aqueous solution in the equimolar ratio 3:1:2. Transparent and bulk single crystals of dimension 9 × 4 ×2 mm3 have been grown from the conventional slow-cooling technique. The crystal structure of the compound has been solved from single crystal X-ray diffraction. The compound 2[C8H4O3]4-Li3+Na+ crystallizes in triclinic system with a space group of Pī having cell dimensions a = 7.5451(2) ? b = 9.8422(3) ? c = 25.2209(7) ? α = 80.299(2);β = 89.204(2);γ = 82.7770(10). FTIR measurement was carried out fo? LiNaP to study the vibrational structure of the compound. The various functional groups present in the molecule and the role of H-bonds in stabilizing the crystal structure of the compound have been explained. Optical absorption properties were studied for the grown crystal using UV-Vis-NIR spectrum. Thermal measurements were carried out for LiNaP to determine the thermal strength as well as to ascertain the hydrated nature of the crystal. Third order nonliner optical studies have also studied by Z-scan techniques. Nonlinear absorption and nonlinear refractive index were found out and the third order bulk susceptibility of compound was also estimated. The results of all studies have been discussed in detail.

基于近红外光谱与多品质指标的苹果出库评价模型研究

富士苹果在贮藏期后熟过程中其生理特性发生变化,不适宜的贮藏会影响出库品质和售卖价格。为使贮藏期果实以较好的品质出库销售,开展对贮藏后熟苹果品质模型研究,并在此基础上对苹果出库进行评价和预测。采集了全贮藏期不同时间苹果样本的近红外光谱和品质指标(可溶性固形物含量、硬度和失重率),分析贮藏期间果实漫反射光谱和品质指标变化规律,基于波长1000~2400 nm范围内的漫反射光谱结合预处理和特征波长提取方法,建立贮藏期苹果品质的偏最小二乘(PLS)和带有反馈的非线性自回归(NARX)预测模型,根据行业标准确定苹果出库品质判断依据,采用基于熵权的TOPSIS法对果实出库品质进行综合评价,实现PLS对品质得分和NARX对多品质指标的预测。结果表明,在预测SSC含量、硬度和失重率时,最优模型分别为CARS-SPA-PLS、CARS-NARX和SPA-NARX,相关系数分别为0.914、0.796和0.918,均方根误差分别为0.511°Brix、0.475 kg/cm^(2)和0.682%;在预测品质得分时,PLS模型的相关系数与均方根误差分别为0.896和0.0434,NARX多输出模型的相关系数分别为0.794、0.785和0.905,均方根误差分别为0.308°Brix、0.492 kg/cm^(2)和0.714%。应用近红外光谱技术能实现对果实贮藏品质监测和出库品质筛选,可为高效贮藏管理技术提供方法。

双光梳光谱测量技术

双光梳光谱技术是一种先进的精密光谱测量技术,具有高分辨力、高频率精度、快速测量和宽带光谱覆盖等优点,已在光谱激光雷达、温室气体监测、燃烧诊断等测量领域中广泛应用。关于双光梳光谱的新原理、新方案和新技术不断涌现,因此有必要对其发展现状进行梳理和总结。本文详细地阐述了双光梳光谱技术的原理和性能指标,分析对比了光频参考、电光调制、单腔双光梳和光调制四种典型双光梳光谱测量系统的实验方案和优势,同时具体分析了双光梳光谱技术在工作波段拓展方向的发展现状,最后对双光梳光谱系统的发展趋势和应用前景进行了总结和展望,为双光梳光谱技术在全波段光谱测量和多场景应用中的进一步提升提供参考。

NIR光谱的Isomap-PLS非线性建模方法

针对样品的近红外（NIR）光谱与其物理化学性质之间存在的非线性关系,提出了一种结合等距映射（Isomap）和偏最小二乘（PLS）的非线性建模新方法。Isomap是一种新的非线性降维方法,属于流形学习方法,能有效地发现高维数据中的本真低维结构。Isomap-PLS建模方法首先用Isomap对高维NIR光谱数据作非线性降维,再用PLS降维并建立校正模型。将Isomap-PLS建模方法分别应用于两个公开的NIR光谱标准数据集,并与PLS单独建模进行比较。结果表明,在两个数据集上,用Isomap-PLS方法建立的校正模型比单独用PLS算法建立的校正模型具有更小的交叉验证均方根误差（RMSECV）;对某些性质数据,Isomap-PLS模型比PLS模型的RMSECV值要小2-5倍。因此,Isomap能够有效反映NIR光谱中存在的非线性结构,Isomap-PLS比PLS具有更好的建模与预测能力。

激光诱导击穿光谱技术/多元二次非线性回归分析土壤中的铬元素

利用激光诱导击穿光谱(LIBS)技术对土壤中铬元素的含量进行了定量分析研究。由于土壤成分复杂r光谱谱线存在较严重的重叠干扰若采用一元回归方法分析常得不到理想结果。为了更充分有效地利用光谱中信息,以土壤中Cr I 425.43 nm和Fe I 425.07 nm谱线的积分强度为自变量,Cr元素浓度为因变量,建立交又降维近似多元非线性回归、多元二次非线性回归和平方降维近似多元非线性回归模型。对比分析表明,当添加Cr和Fe元素特征谱线强度交又项影响时,所建立的多元二次非线性回归模型效果最佳,预测浓度与实际参考浓度之间线性关系达到0.9943,预测4个验证样品的相对误差分别为3.57%,0.76%,7.66%和2.24%。

DOAS方法在线测量污染气体浓度的温度与非线性补偿

差分吸收光谱法(DOAS)应用于固定污染源烟气排放监测时,烟气温度及气体的非线性吸收对准确测量气体浓度影响较大,必须对温度及非线性吸收的影响进行修正。文中分别提出了新的温度补偿及新的非线性补偿方法,即将不同温度下气体的分子数密度与20℃下气体的分子数密度之比与温度的对应关系拟合出温度补偿函数,将气体实际浓度所对应的分子数密度与反演结果所对应的分子数密度之比与反演结果之间的对应关系拟合成非线性补偿函数,利用这两个补偿函数对浓度反演结果进行补偿。对14914mg/m^3的SO_2气体在70～170℃温度范围内的实验研究结果表明,新的温度补偿及非线性补偿函数能很好的补偿温度及非线性的影响,具有较高的气体浓度反演精度。

TDLAS氧气测量系统中激光器调谐性能测试与优化

TDLAS(可调谐半导体激光吸收光谱)技术以其分子光谱高选择性、速度快、灵敏度高、非接触测量等难以取代的优势,成为燃烧过程诊断等应用的首选,可以有效用于氧气测量。DFB(分布反馈)半导体激光器以其体积小、功耗低、寿命长、线宽窄、波长可调谐等优点成为TDLAS系统的主要选择,而其调谐特性是制约系统测量性能的关键因素。根据TDLAS氧气测量系统工作要求,采用一种简单易行的实验方法对系统中用到的764 nm DFB激光器的电流波长、温度波长和电流功率等重要调谐特性进行了测试和分析,发现出射光谱窄线宽、高边模抑制比和宽波长可调谐范围等特点明显,电流波长调谐曲线近似但并非严格线性、调谐速率约0.023 n·mA^(-1),温度越高阈值电流越大、PI曲线也并非严格线性,温度调谐特性曲线线性较好、波长温度调谐速率基本保持恒定约为0.056 nm·℃^(-1)。可见各种调谐曲线的非线性失真比较明显,影响氧气测量精度。温度调谐非线性可以通过温控精度的提高来消除,电流功率调谐非线性可以通过设置参考光强来消除。为了进一步解决电流波长调谐非线性问题,根据DFB半导体激光器的调谐机理和电流波长测试结果的多项式拟合,考虑通过DA控制注入电流的方式对电流波长调谐非线性进行补偿。这种方法针对不同激光器只需在系统初次工作之前进行一次多项式拟合,方案合理、实现简单且不影响测量过程。实验证明,补偿之后的λI曲线线性拟合残差小于1 pm,远小于补偿前的22 pm,效果明显,为氧气各种参数TDLAS精确测量和反演提供了依据。

弹光调制非线性光程差干涉信号的快速反演

为了提高弹光调制中非线性光程差干涉信号的光谱反演效率,采用非均匀快速傅里叶变换算法对弹光调制相位非均匀采样干涉信号反演光谱进行了仿真,得到1024点反演速率较直接计算提高20倍,平均误差达到0.87%的结果。结果表明,该算法可实现弹光调制干涉信号的快速、高精度反演,给硬件实现弹光调制反演光谱提供了一定的参考依据。

采用激光诱导击穿光谱技术测定合金钢中锰和硅的含量

基于激光诱导击穿光谱(LIBS)技术定量分析多品种合金钢中锰(Mn)和硅(Si)的浓度,采用的校正方法为多元二次非线性函数定标方法。分析的钢种有普通合金钢、不锈钢、碳素工具钢等。由于不同钢种在基体组成上存在较大差异,而且钢的光谱还存在复杂的谱线重叠干扰,所以受基体效应影响严重。因此,对钢这类复杂化学体系物质的定量分析,若采用单谱线信息的校正方法会造成很多有用信息的丢失,而采用多变量的定标法会更充分利用光谱中的信息,更有效校正多基体组分的基体效应,进而提高LIBS定量分析的重复性和准确性。相比线性标准定标曲线法,测量结果的相对标准差从20%以上降低到10%以下,Mn元素测量结果的准确度提高了5倍多,Si元素提高了6倍多。

支持向量回归建立成品汽油通用近红外校正模型的研究

针对目前采用偏最小二乘法建立成品汽油分析模型存在的问题,采用近几年新兴的支持向量回归方法建立了多种汽油标号通用的校正模型,其预测能力优于对应的偏最小二乘法,对汽油研究法辛烷值、烯烃和芳烃的预测标准偏差分别为0.37、1.28%和1.38%,可应用于实际的汽油管道自动调合近红外光谱在线分析。