Measurement of CO2 concentration based on supercontinuum laser absorption spectroscopy

The concentrations of CO₂ were measured by the supercontinuum laser at normal temperature and variable temperature accurately in this paper. The absorption spectra of CO₂ at different concentrations(1.2%—9.0%) were measured in the wavelength range of 1 425—1 445 nm under the optical path of 26.4 m at 293 K and 1 atm. The experimental results showed that the positions of the primary and secondary absorption peaks(1 432 nm, 1 437 nm) were consistent with the HITRAN database. A linear model of concentration and signal intensity at 1 432 nm was established. The maximum relative error of the concentration measurement was 3.3%. The line intensities of 99.9% CO₂ in the 1 425—1 445 nm at different temperatures(298—373 K, interval of 15 K) were measured. The influence of temperature changes on the concentration measurement result was corrected and the relative error of the concentration measurement was reduced to 1.4%. Finally, the source of the uncertainty of the entire spectrum measurement system was analyzed and evaluated. This paper demonstrate that the supercontinuum laser can achieve the long-distance measurement of the CO₂ under normal temperature or variable temperature environment accurately, which provide an important reference for the long-distance gas detection on site and simultaneous detection of multi-component gases.     

Study on energy threshold and spectral characteristics with spot radius based on LIBS technology

The aim of this study is to investigate the relationship between the laser-induced optical breakdown energy threshold and the spectral signal changes with the spot radius. First of all, using the avalanche breakdown threshold theory calculates the threshold avalanche ionization rate ηc. Combining with the theory of light intensity distribution and the relationship between pulse energy and peak power, numerical calculations have obtained the law of change of spot radius and threshold laser energy. Secondly, the variation of the spectral signal-to-noise ratio (SNR) with the laser energy is measured according the experimental measurement, and the threshold laser energy required for optical breakdown at different spot radius is obtained. The theoretical threshold model of the relationship between the threshold laser energy and the quadratic function of the spot radius obtained by numerical calculation is verified, and it is revised, the results show that the relative error between the revised theoretical threshold model and the experimental threshold model is less than 5.3%. At last, the influence of the spot radius on the spectral signal and electron density is also analyzed, it is found that both the spectral intensity and the electron density have a maximum at the spot radius of 11 μm. The results show that it is necessary to find the best spot radius during the laser induced breakdown spectroscopy (LIBS) experiment. This provides a reliable theoretical basis and experimental reference for further study of the influence of spot radius on LIBS technology measurement.     

基于背景扣除法消除土壤基底中Al元素干扰的LIBS实验研究

土壤中重金属的污染严重影响了农业和食品安全，因此，对重金属污染的高效、准确的检测是目前亟需解决的问题。采用激光诱导击穿光谱技术（Laser induced breakdown spectroscopy，LIBS）对土壤中Ni元素进行定量分析时发现，土壤中波长为373.68 nm的Ni元素的特征峰会受到Al元素在373.39 nm处谱线的影响，因此，将纯铝基底土壤光谱与压片土壤光谱进行了对比测量。提出了以纯Al作为基底，采用纯Al基底谱线扣除土壤背景中Al元素谱线的方法，来消除土壤背景中Al元素对Ni元素干扰，该方法被称为背景扣除法。实验确定了两种土壤样品的最佳延迟时间均为1.0 μs，透镜到样品的距离（Lens to sample distance，LTSD）分别为97 mm和96 mm。采用内标法对两种土壤样品中的Ni进行了定量分析，得到纯Al基底土壤样品中Ni元素的定标曲线拟合效果较好，相关系数R2为0.997，最大标准偏差（Relative standard deviation，RSD）为4.34%，采用基底背景扣除法后的纯铝基底土壤样品中Ni元素检测的相对误差降低到4%。实验结果表明:采用LIBS技术对土壤中重金属元素含量测量时，在元素特征谱线有限的情况下，为避免谱线干扰，提高检测精度，采用背景扣除的方法能够有效消除元素间的谱线的干扰。     

基于磁场约束下激光诱导击穿光谱技术的重金属检测研究

为提高激光诱导击穿光谱(laser induced breakdown spectroscopy, LIBS)技术定量分析的精度,开展了磁场约束下LIBS技术对土壤中重金属元素检测的研究,并采用多谱线强度归一化内标法进行数据处理。通过比较磁场强度分别为0 T、0.3 T、0.8 T、1.25 T时的光谱特性,得到光谱强度和信噪比(signal-to-noise ratio,SNR)随磁场强度增大而增大,在1.25 T磁场强度时,样品元素Cd和Cu的光谱强度和SNR要比无磁场作用分别增强了34.77%、56.33%和40.83%、74.12%,构建了磁场强度为1.25 T时的Cd和Cu元素定量分析模型。结果显示,相对于传统内标法,采用多谱线强度归一化内标法的元素检测限分别从52.78 mg/kg和49.18 mg/kg降低到23.87 mg/kg和18.06 mg/kg;相关系数分别从0.961 3和0.942 7提高到0.996 9和0.999 3。本实验研究改善了LIBS的光谱特性,提高了定量分析的精度,采用多谱线强度归一化内标法降低了重金属的检出限和测量误差。     

基于平面反射镜约束的激光诱导击穿光谱技术研究北大核心CSCD

为改善激光诱导击穿光谱技术(laser-induced breakdown spectroscopy,LIBS)的光谱特性,搭建了平面反射镜约束下的LIBS检测系统,将平面反射镜放置于样品两侧,分别选取平面反射镜间距7 mm,9 mm,11 mm,13 mm开展实验,得到等离子体辐射强度随平面反射镜间距增加而减小。研究了不同平面反射镜间距对土壤样品中Fe,Al,Pb 3种元素等离子体特性的影响,实验结果显示:相比于无平面反射镜约束,在平面反射镜间距为7 mm时,样品中Fe I,Al I,Pb I等3种元素的信噪比分别提高了29.9%,39.4%,31.0%;计算得到等离子体温度提高了484.54 K,等离子体电子密度提高了2.41×10^(15)cm^(-3)。对有无平面反射镜约束下的Pb元素进行定量分析,得到检测限从86.9 mg/kg降低到51.2 mg/kg,相对标准偏差从7.8%降低到4.6%。可见,利用平面反射镜是改善激光光谱特性的一种简单有效的方法。     

Plasma characteristics and quantitative analysis of Pb and Ni in soil based on LIBS technology

When measured by laser induced breakdown spectroscopy, the characteristic parameters of the plasma fluctuate significantly with the experimental parameters, which would have a greater impact on the quantitative measurement. The effects of two experimental parameters, lens to sample distance(LTSD) and delay time, on plasma temperature and electron density were analyzed. Thereafter the optimal LTSD and delay time for quantitative analysis of Pb and Ni in soil were identified. Two element calibration curves were calculated by the internal standard method under the optimal LTSD and delay time. About the two elements, correlation coefficient of the calibration curves is above 0.993. The maximum relative standard deviation(RSD) were 4.47% and 4.76%, respectively, and the maximum relative errors were 12% and 4.8%, respectively. The experimental results showed that laser induced breakdown spectroscopy method in combination with plasma characteristic parameter analysis shows the advantage on quantitative analysis of heavy metals in soil.     

恒流源对近红外光谱传感器测量不确定度的影响

近红外光源的稳定性影响近红外技术的可靠程度.提高其电源的稳定性,可提高近红外光源的稳定性,改善实验室近红外技术在气液两相流的应用.使用高精密恒流源为近红外光源供电,进行了实验研究,结果表明:使用高精密恒流源时,近红外光源更稳定,输出电压值也更加稳定可靠,输出电压值的极差在0.12左右,标准差不超过0.008 38;而在...     

Research on the identification of the production origin of Angelica dahurica using LIBS technology combined with machine learning algorithms

The origin of Angelica dahurica medicinal herbs varies, and their pharmacological effects also differ. In order to achieve rapid and accurate identification of the origin of Angelica dahurica medicinal herbs, this study utilizes laser induced breakdown spectroscopy(LIBS) technology combined with machine learning algorithms to identify the original source of Angelica dahurica. Sliced samples of Angelica dahurica were taken from four regions: Hebei, Henan, Zhejiang, and Sichuan. The spectral data ...     

Research on the measurement of CH4 concentration based on dual-band weighted combination model

A detection system based on supercontinuum laser absorption spectroscopy (SCLAS) technology was built up in this study. The absorption spectra of CH4 in different near-infrared bands were measured based on the SCLAS detection system. Under normal temperature and pressure, the absorption spectra of CH4 at different concentrations in the bands of 1 319—1 339 nm and 1 656—1 676 nm were measured. The linear models of CH4 concentrations in different bands were established. The fitting coefficient (R2) of the models were 0.995 7 and 0.996 1, respectively. In order to improve the concentration inversion ability of the model, the weight distribution of each model was determined by R2 and sum of squared error (SSE) to obtain a new combined model. The maximum relative error of the concentration inversion was reduced from 2.3% to 1.3%. The experimental results show the feasibility of applying the SCLAS technology to CH4 concentration measurement, and it also verifies that the dual-band combination model can improve the accuracy and stability of the CH4 concentration measurement.