火焰发射光谱对K元素激光诱导击穿光谱测量的影响

在煤和生物质燃烧过程中,燃料中的碱金属元素会发生气态释放,并在随烟气降温的过程中凝结,产生热力设备结渣、腐蚀、积灰等问题,影响设备的安全运行。激光诱导击穿光谱(LIBS)技术是测量煤/生物质火焰中碱金属元素分布的有效手段。建立了一套火焰场内K元素的LIBS测量系统,分别测量了不同ICCD门宽时间条件下火焰场内K元素的火焰发射光谱(FES)信号和LIBS信号,并计算、比较了二者的信号强度随测量系统ICCD门宽时间变化的规律。实验结果表明,相同ICCD门宽时间条件下,火焰场内K元素LIBS信号强度显著高于FES信号强度。随着ICCD门宽时间的增加,二者的信号强度均逐步增加,但是二者的增速变化规律并不相同:K元素LIBS信号强度的增加速度呈现出先快后慢的变化规律;K元素FES信号强度则呈现出线性增加的规律。同时,相同ICCD门宽时间条件下,K元素LIBS信号强度与FES信号强度的比值在ICCD门宽时间为0~8μs的范围内迅速升高至约4;之后,随着ICCD门宽时间的增加,该比值缓慢下降并逐步趋近于1。通过分析火焰场内K元素FES对LIBS测量影响的原理,提出了合理选取LIBS测量系统ICCD门宽时间,使得K元素LIBS信号强度与FES信号强度的比值最大化,从而降低K元素FES对LIBS测量影响,优化了提高火焰场内K元素LIBS信号测量准确度的方法。     

激光诱导击穿火焰等离子体光谱研究

采用PI-MAX-II型增强型电荷耦合器件, 用Nd:YAG纳秒脉冲激光器输出的1064 nm强光束击穿在一个大气压的空气中燃烧的酒精灯火焰, 对激光诱导击穿酒精灯火焰产生的等离子体光谱进行了初步研究. 根据美国国家标准与技术研究院原子发射谱线数据库, 对等离子体中的主要元素的特征谱线进行了标识和归属. 通过激光诱导击穿空气等离子体光谱、激光诱导击穿酒精灯火焰等离子体光谱、激光诱导酒精喷灯火焰等离子体光谱的对比分析, 发现不同燃烧状况下的光谱中各原子谱线的相对强度是不同的. 这些结果对于使用激光诱导击穿技术分析和研究碳氢燃料在空气中的燃烧特性具有重要的意义和参考价值, 同时也为将该技术应用于燃烧诊断提供了实验依据.     

土壤中铜元素的激光诱导击穿光谱测量分析

利用Nd:YAG脉冲激光器(1064nm)作为光源,以高分辨率、宽光谱段的中阶梯光栅光谱仪和ICCD为谱线分离与探测器件,测量并分析了土壤中铜元素激光诱导击穿光谱特性。以铜的327.396nm特征谱线作为分析线,在同一浓度下,固定探测器门宽,通过调节延迟时间,得到铜元素的衰变特性,确定了铜元素的最佳延迟时间为1.1μs。测定不同铜浓度下的特征谱线强度,表明在低浓度下,谱线强度随浓度的增加而增大。文章给出了铜元素的定标曲线,并计算得到铜元素的检测限为13.36μg·g-1。     

土壤中砷元素的激光诱导击穿光谱测量分析

利用Nd:YAG脉冲激光器作为光源,在实验室自然大气环境下诱导产生国家标准土壤的激光等离子体,选取砷的228.8 nm特征谱线作为分析线,测量并分析了砷元素的激光诱导击穿光谱特性。在相同含量和积分时间条件下,调节延迟时间,获取了砷元素的时间演化特性。确定砷元素的最佳延迟时间为1 s,积分时间为2 s。测定不同含量下,砷的特征谱线强度,给出砷元素的定标曲线,并计算得到砷元素的检测限为45 mg/kg。     

用激光诱导击穿光谱测量铝合金的激光烧蚀阈值

采用正交几何配置的双波长双脉冲激光烧蚀-激光诱导击穿光谱技术准确测量了铝合金样品的激光烧蚀阈值。在烧蚀激光波长为532 nm、脉宽为12 ns并采用焦距为2 cm的非球面透镜强聚焦的条件下,得到铝合金的激光能量烧蚀阈值为48 J,等效的能量密度烧蚀阈值为9.8 J/cm2。该技术是一种新的激光烧蚀阈值的光谱测量手段,与传统的测量技术相比,具有高灵敏、准确、快捷和便利的特点,可以用于不同材料的激光烧蚀阈值的准确测量。     

用激光诱导击穿光谱测量铝合金的激光烧蚀阈值

采用正交几何配置的双波长双脉冲激光烧蚀-激光诱导击穿光谱技术准确测量了铝合金样品的激光烧蚀阈值。在烧蚀激光波长为532 nm、脉宽为12 ns并采用焦距为2 cm的非球面透镜强聚焦的条件下,得到铝合金的激光能量烧蚀阈值为48 J,等效的能量密度烧蚀阈值为9.8 J/cm2。该技术是一种新的激光烧蚀阈值的光谱测量手段,与传统的测量技术相比,具有高灵敏、准确、快捷和便利的特点,可以用于不同材料的激光烧蚀阈值的准确测量。     

土壤中铜元素的激光诱导击穿光谱测量分析

本文采用波长为532 nm的Nd:YAG单脉冲纳秒激光器诱导激发土壤(样品土壤来自蚌埠学院校园),并分析测量了土壤中铜元素的激光诱导击穿光谱特性.以铜元素的特征谱线Cu(393.3 nm)作为分析线,优化了实验参数增强型光电耦合器件(ICCD)门宽,ICCD门延迟对等离子体信号的影响,并在优化后的实验条件下测量分析了土壤中的金属元素种类.实验结果表明优化后的实验参数:ICCD门宽500ns,ICCD门延迟500 ns;在该优化条件下检测到样品土壤中含有金属元素:Fe, Cr, Ca, Mg, Cu, Al, Mn.     

CuSO_4溶液中Cu元素浓度的激光诱导击穿光谱测量研究

利用激光诱导击穿光谱技术对CuSO4溶液中的Cu元素浓度进行实验测量。利用配置的七种浓度的CuSO4溶液,采用统计探索性数据分析方法给出了Cu元素定标曲线,其拟合度系数R2大于0.98,激光诱导击穿光谱的平均相对偏差值为6.9%,Cu元素的平均最小检测限为12ppm。利用去一交互检验方法采用分析谱线CuⅠ324.75nm和CuⅠ327.40nm对应的七种溶液的平均测量相对误差分别为6.52%和5.86%。当Cu元素浓度在10ppm时实验相对误差较大,其值为10.3%,而浓度达到2 000ppm时相对误差值减小,仅为1.1%,说明LIBS技术在溶液较低元素浓度检测方面的准确度有待提高。研究结果表明激光诱导击穿光谱技术在环境水污染重金属元素检测方面具有潜在的应用前景。     

基于激光诱导击穿光谱技术的铝合金成分定量分析

利用Nd:YAG激光器输出的532nm激光束对位于空气中的标准变形铝合金样品进行烧蚀产生了激光诱导等离子体.对测量的230—440nm波长范围的光谱进行了谱线标定,同时基于自由定标方法对样品成分进行了定量分析,确定了样品中的元素含量.分析结果与标准值具有较好的一致性.     

铀元素的激光诱导击穿光谱测量分析

为促进LIBS技术在微量重金属元素检测以及核污染检测领域的应用,提高检测灵敏度和准确性,采用了激光双脉冲LIBS技术和光电双脉冲LIBS技术,分别对土壤和二氧化硅中的铀元素进行分析。首先,对激光脉冲能量、电压和采集延时等参数进行优化,提高铀元素特征谱线的强度和信噪比;然后在优化实验参数条件下,对含不同浓度铀元素的土壤样品和二氧化硅样品进行激发;选取UII 367.01 nm、 UII 454.36 nm两条铀元素的特征谱线作为分析线,通过铀元素浓度与特征谱线强度的线性关系,建立定标曲线。双脉冲激光激发条件为：激光脉冲1作为预脉冲,主要参数为1 064 nm, 90 mJ, 9.2 ns,激光脉冲2作为再加热脉冲,主要参数为355 nm, 50 mJ, 8 ns,两个脉冲的时间间隔800 ns,光谱采集相对第二个脉冲延时1μs,得到铀元素在土壤和二氧化硅两种样品中的浓度检测下限分别为572和110 mg·kg^-1,拟合优度值R²分别为0.958和0.999。在光电双脉冲激发条件下,激光脉冲作为预脉冲,主要参数为355 nm, 50 mJ, 8 ...     

Single-shot two-dimensional measurement of nanoparticles in turbulent jet-diffusion flames using phase-selective laser-induced breakdown spectroscopy

In this work, we demonstrate a single-shot two-dimensional measurement of vanadic oxide (V₂O₅) nanoparticles in a turbulent jet-diffusion flame based on phase-selective laser-induced breakdown spectroscopy (PS-LIBS). By collecting the atomic spectra of vanadium near 439?nm from nano-sized plasmas within the ～30?ns lifetime, particle information can be revealed without interference from elastic scattering or Bremsstrahlung emissions. As the laser intensity increases, the signal intensity first increases and then saturates when the laser intensity reaches 0.5 GW/cm². In the saturation regime, a proportional correlation is established between the signal intensity and the particle volume fraction. Based on the parametric study in the laminar condition, we image the instantaneous distribution of particle volume fraction in the turbulent condition using single-shot PS-LIBS measurements. The snapshots show that vanadic oxide nanoparticles concentrate near the diffusion flame surface, which may be caused by the rapid formation of particles on the oxidizer/precursor side and quick dilution across the reaction layer. The Proper Orthogonal Decomposition (POD) analysis further indicates that the fluctuations of the particle volume fraction originate from the unsteady flame surface at the upstream positions and large-scale mixing at the downstream positions. The single-shot PS-LIBS measurement shows promising potential for resolving complex processes of particle formation in turbulent flame synthesis.     

Quantitative analysis of cement powder by laser induced breakdown spectroscopy

Determination of elemental composition of cement powder plays an important role in the cement and construction industries. In the present paper, Laser induced breakdown spectroscopy (LIBS) is used for measuring the concentration of cement ingredient. Cement powder samples are pressed into pellets. Laser pulses are focused on the surface of pellets. A microplasma is formed in the front of samples. The plasma emission contains information about the elemental composition of the samples. By assumption of local thermodynamic equilibrium (LTE) and using several standard cement samples, a calibration curve is prepared for each element. The major and minor elements of cement such as Ca, Si, K, Mg, Al, Na, Ti, Mn and Sr are qualitatively and quantitatively determined. For verification of LTE conditions, plasma parameters such as plasma electron temperature and electron density are computed. According to the obtained results, the LIBS technique could be a suitable method for determination of elemental composition in the cement production industries.     

Spectroscopic characterization of aluminum plasma using laser-induced breakdown spectroscopy

A detailed investigation of aluminum plasma induced by a 1064 nm Nd:YAG laser in air was performed. The emission of spectral lines arising from Al I transition at 396.07 nm, Al II transition at 358.46 nm, Al III transition at 360.72 nm and Al IV transition at 363.05 nm were well-resolved. The plasma parameters including electron temperature and electron density were determined through the Boltzmann plot method using the emission line intensities of the same ionized stages of aluminum atoms and the Stark-broadening profiles of Al II emission line, respectively. The temporal evolutions of the spectral lines belonging to atomic and ionic aluminum elements and the plasma parameters were investigated at three different laser pulse energies. Moreover, the validity of local thermodynamic equilibrium was elucidated in our experimental condition.     

A review of laser-induced breakdown spectroscopy signal enhancement

A review of the methods of signal enhancement in laser-induced breakdown spectroscopy (LIBS) is presented. Conventional LIBS suffers from disadvantages of low sensitivity and high limits of detection compared with other analytical techniques, such as inductively coupled plasma mass spectrometry. During the last two decades, various methods have been applied to LIBS in order to realize highly quantitative and qualitative analysis. Current approaches include double-pulse excitation, spatial or magnetic confinement, spark discharge, etc. Different configurations of experimental setups and conditions are suggested for the realization of these improved techniques, while various parameters influence significantly on the enhancement effect. With the aim to study the laser ablation process and characterize the effectiveness of each method, several parameters such as plasma volume and emission intensity are reviewed. Several suggestions are proposed to explain the mechanism of each enhancement method. These modified techniques have been applied on various materials and fields.     

The high dependence of polarization resolved laser-induced breakdown spectroscopy on experimental conditions

It is shown that the continuum emission produced by an Al alloy ablated by femtosecond laser pulses is much more polarized than the characteristic lines of elements. A Glan-Thomson polarizer is used in the laser-induced breakdown spectroscopy experiment to investigate the polarization effect. The use of the polarizer at its minimal transmission increases the signal-to-noise ratio. The effects of angle of detection, focal position, and pulse energy on the signal-to-noise ratio are also studied.     

激光诱导Ca等离子体温度的实验研究

等离子体温度是激光诱导击穿光谱测量中一个重要的因素。采用Nd:YAG脉冲激光器作为光源击穿样品形成等离子体,其发射光谱由中阶梯光栅光谱仪和ICCD进行分光和光电转换。通过实验得出了300~450 nm波段的光谱图,定性分析出了Ca Ⅱ 315.9, 317.9, 393.4, 396.9 nm和Ca Ⅰ 422.7 nm等发射谱线。根据激光诱导击穿光谱定量公式,等离子体温度的变化对谱线强度有影响。先假设实验中等离子体处于局部热平衡状态,选用Ca的4条一价离子谱线,根据Boltzmann斜线法计算出了等离子体温度,并得到了等离子体温度与Ca质量分数的关系。随着Ca质量分数的增加,等离子体温度也相应增加。但当Ca质量分数小于0.50%时等离子体温度增加的幅度较小,而质量分数大于0.50%时等离子体温度的上升幅度相对较大。最后经过验证,实验中等离子体处于局部热平衡状态的假设成立。