Interaction of excess electrons with water molecules at the early stage of laser-induced plasma generation in water

Forward and backward stimulated Raman scattering (SRS) of OH stretching vibrations are measured when an intense 40 ps pulsed beam is focused into water. Characteristic features related to the interaction of OH groups with excess electrons generated by the strong laser irradiation are observed. The SRS spectra are indicative of the important role which excess electrons play in transient enhancement of the SRS at the initial stage of laser-induced plasma generation in water. The hydration structures around the excess electrons in water are also discussed.     

Raman Scattering in Light and Heavy Waters

We present the results of an experimental study of the spontaneous and stimulated Raman scattering (SRS) spectra and luminescence spectra of light and heavy waters. Also we investigate various samples of light water. We show the possibility of using spectral methods to detect impurities in water and determine the degree of its structuredness, which can serve as an additional criterion of the water quality. We find a fine structure in the SRS spectrum of heavy water in the low-frequency region.     

水溶液中微量Cu元素的激光诱导光谱检测

采用普通打印纸作为基底置于含有痕量重金属离子的水溶液中,用于富集溶液中的重金属Cu元素,烘干后用激光诱导击穿光谱进行定量分析。该方法克服了用激光诱导击穿光谱方法直接分析液相样品中重金属含量时存在水的溅射和灵敏度低等不足。实验中选用324.7 nm的光谱线作为分析线,研究了光谱强度与富集时间的关系,建立了用于溶液中Cu元素定量测量的校正曲线,检测限达到0.023 mg·L-1。为水体中重金属检测提供了一个可行的具有良好灵敏度分析技术。     

Enhancement CH-SRS of benzene mixing with toluene in liquid-core optical fiber at a low excitation power

Stimulated Raman scattering (SRS) of benzene mixing with toluene is studied in liquid-core optical fiber (LCOF) at a low excitation power 3 mJ/pulse. We obtained the intensive SRS of CH stretching vibration at 3060 cm^?1 [CH-SRS]. Neat benzene or toluene does not show the CH-SRS line under the same experimental condition. The CH-SRS threshold at 3060 cm^?1 for the binary solution was 2.5 mJ/pulse. The results suggest that interaction in molecular vibrations can generate strong CH-SRS in LCOF, we assume that the main mechanism of these phenomena to be the laser-induced plasma (LIP) enhancement to CH-SRS, which may provide a simple way to investigate the intermolecular interaction.     

Stimulated raman scattering in fiber-optic communication lines

Stimulated Raman scattering (SRS) in a long-distance fiber-optic communication line with wavelength-division multiplexing (WDM) is studied theoretically at a high power of the signal transmitted. A new criterion for determining the SRS threshold is used to calculate the critical input power versus the number of optical channels and frequency separation between them. The theoretical model is verified experimentally. SRS interaction between two channels in a communication line with an SRS amplifier for which the optical waveguide of the line serves as a nonlinear medium is measured.     

Enhanced stimulated Raman scattering in H<Subscript>2</Subscript> by seeding an SRS line into an H-ɛ Balmer line: Amplification-coupled laser wavelength shifter

The stimulated Raman scattering (SRS) in H₂ gas above the dissociation energy limit was recorded using a 266-nm UV laser. All of the observed Stokes and anti-Stokes SRS lines showed a normal behavior except the third Stokes SRS lines at 397.8 nm, which showed a substantial intensity enhancement of about a 36%-conversion efficiency of the pump energy. This enhancement in the SRS line is attributed to the seeding of the SRS line into the Balmer H-? line at 397 nm in molecular hydrogen. To the best of our knowledge, there is no report of any work on enhanced stimulated Raman scattering in H₂ by the seeding of the H-? Balmer line into the SRS line and attaining a very high intensity at the third Stokes SRS lines at 397.8 nm. The cell pressure and the laser pulse energy dependence of these SRS lines substantiate our explanation.     

Effect of crystal orientation on picosecond-laser bulk microstructuring and Raman lasing in diamond

In the paper we report on picosecond-laser bulk microstructuring and stimulated Raman scattering (SRS) in type IIa single-crystal diamond in the course of multipulse irradiation at λ=532 nm wavelength using an advanced ps-laser system equipped with additional setups for on-line video imaging and photoluminescence spectra measurements. The effect of crystal orientation (relative to the incident laser beam) on (i) optical breakdown thresholds, (ii) character of bulk modifications, and (iii) generation of stimulated Raman scattering in diamond during irradiation with picosecond pulses of different durations (τ ₁=10 ps and τ ₂=44 ps) is studied. It is shown that the processes of laser-induced breakdown in the bulk of diamond (at the backside of the crystals) and bulk microstructure growth are governed by the dielectric breakdown mechanism. It is found that generation of high-order stimulated Raman scattering in diamond crystals has a considerable effect on the threshold of laser-induced breakdown and bulk microstructuring. Conditions of the efficient SRS lasing are determined, depending on the pulse duration and the direction ([100] and [110]) of the laser beam incidence. A method of local temperature measurements in the bulk of diamond based on the Stokes-to-anti-Stokes intensity ratio in the recorded SRS spectra is proposed, its applicability to determine a “pre-breakdown” temperature of diamond during multipulse ps-laser irradiation is discussed.     

YVO4晶体的高效受激拉曼散射

报道了YVO4晶体在532 nm、30 ps脉冲下的的高效受激拉曼散射。采用腔外单次通过方式测量了不同长度YVO4晶体1阶斯托克斯受激拉曼散射的阈值,并得到该晶体的稳态增益系数为16.0±0.5 cm/GW。实验中观察到2阶斯托克斯线(558.6 nm5、87.8 nm)和1阶反斯托克斯线(508.0 nm),受激拉曼散射的整体转换效率高于50%。     

基于电极富集的水体重金属LIBS检测灵敏度研究

为了提高水体重金属LIBS检测的灵敏度以及降低元素检测限,采用LIBS结合铝电极富集方法对水体中的重金属Pb, Cd, Ni进行了分析。研究并优化了电极富集方法中关键参数—富集电压U,分析了LIBS特征谱线的光谱强度与富集电压大小之间的关系,得出重金属元素特征光强随着富集电压先增加后减小,在1.2 V处光谱强度达到最大值,选择了最优富集电压值为1.2 V。研究了Pb,Cd,Ni三种重金属元素的光谱稳定性,其特征谱线光谱强度的相对标准偏差(RSD)分别为5.98％,4.25,％和5.27％,说明该实验方法得到的谱线具有较高的稳定性。在0～ 0.13 mg·L-1范围内配制系列样品进行实验并对元素进行定量分析,得到Pb,Cd,Ni三种重金属元素的检测限分别为1.2,3.1和1.7 ppb。结果表明：LIBS结合铝电极富集方法能够有效地提高特征谱线的稳定性以及降低元素的检测限,为提高水体重金属LIBS的检测灵敏度和分析能力提供了方法支持。     

Low-Frequency Stimulated Raman Scattering on Acoustic Vibrations of Dielectric Nanospheres in Aqueous Suspension

A low-frequency SRS (LFSRS) signal is detected at a certain dielectric nanoparticle (latex spheres) concentration in an aqueous suspension. The SRS line shift is close to its estimate by the “transverse” hypersound speed in latex.     

C2H2分子受激Raman光谱中的光学Stark效应研究

本文研究了C₂H₂分子受激Raman光谱(SRS)中的光学斯塔克(Stark)效应,同时还研究了激光功率以及单一转动态量子数J与Stark效应的关系.实验表明:C₂H₂分子在高强度激光电场作用下,它的SRS由于光学Stark效应产生明显的非对称加宽,利用Stark线型加宽数值模拟,从理论上计算了Raman光谱线型,与实验的SRS线型比较,二者符合程度相当好.     

Saturation of backward stimulated scattering of a laser beam in the kinetic regime

Stimulated Raman (SRS) and Brillouin scattering (SBS) are examined in the kinetic regime using particle-in-cell simulations. Wave front bowing of electron-plasma waves (ion-acoustic waves) from trapped particle nonlinear frequency shift is observed in the SRS (SBS) regime for the first time. Self-focusing from trapped particle modulational instability (TPMI) is shown to occur in 2D and 3D SRS simulations. The key physics of SRS saturation is identified as a combination of wave front bowing, TPMI, and self-focusing: Bowing marks the beginning of SRS saturation and self-focusing terminates SRS. Ion-acoustic wave bowing also contributes to SBS saturation. Velocity diffusion by transverse modes and rapid loss of hot electrons in regions of small transverse extent formed from self-focusing dissipate wave energy and increase Landau damping, despite trapping that reduces Landau damping initially.     

水中受激拉曼散射的能量增强及受激布里渊散射的光学抑制

为提高液体介质中受激拉曼散射的输出能量,提出了通过温度调控来抑制受激布里渊散射的方法,设计了532 nm多纵模宽带脉冲激光泵浦的受激拉曼散射发生系统,测量了不同温度下水中前向受激拉曼散射及后向受激布里渊散射的输出能量,分析了水温、泵浦激光线宽及热散焦效应对受激拉曼散射输出能量影响的物理机制.实验结果表明:通过降低水温可实现对受激布里渊散射过程的有效抑制,同时减小热散焦效应带来的光束畸变,从而有效提高受激拉曼散射的输出能量.研究结果对液体介质中的受激拉曼散射多波长转换具有重要意义.     

水中镉含量的激光诱导击穿光谱高灵敏快速检测

 为了对水中的痕量镉进行高灵敏快速检测,实验采用一种未受污染的薄木片作为基底来吸收水样品,将其晾干后再用激光诱导击穿光谱（LIBS）技术对其进行分析,克服了用LIBS技术直接分析水样品时灵敏度低和稳定性差等问题。实验中选择214.44 nm的镉离子线作为分析线以提高光谱检测的灵敏度,建立了用于定量分析的校正曲线,镉的检出限达到55 μg/L,重复测量的信号相对标准偏差小于5%,单次测量的时间短于5 min。     

水体重金属激光诱导击穿光谱定量分析方法对比研究

建立了适用于激光诱导击穿光谱探测的多元线性回归、神经网络回归和支持向量机回归三种定量反演算法模型, 以水体重金属Ni为例进行了回归实验测试和对比分析. 多元线性回归、神经网络回归和支持向量机回归的平均相对标准偏差分别为7.60%, 4.86%, 2.35%; 最大相对标准偏差分别为23.35%, 15.20%, 8.29%; 平均相对误差分别为25.98%, 10.58%, 2.72%, 最大相对误差分别为116.47%, 47.38%, 9.89%. 研究为进一步实现水中痕量金属元素的快速定量分析提供了方法和数据参考. 关键词： 光谱学 激光诱导击穿光谱 支持向量机回归 重金属     

Investigation of collisionally induced stimulated scattering in sodium vapor with temporal and spectral resolution

In this work we present fully time-resolved spectra of Amplified Spontaneous Emission (ASE) and Stimulated Raman Scattering (SRS) in sodium vapor. We observe that the ASE signal precedes the SRS emission, and the peak of the amplified Stokes pulse is delayed with respect to the peak of the laser pulse. The time evolution of the line widths of the ASE and Raman signals is also shown. We find that the line widths of the stimulated fluorescence component (ASE) and the stimulated Raman radiation change with time. Both spectra start as small narrow fluctuating lines, then the line widths reach maximum values and thereafter decrease with time.     

Determination of Cr in water solution by laser-induced breakdown spectroscopy with different univariate calibration models

In order to prove the feasibility of laser-induced breakdown spectroscopy (LIBS) in measuring toxic metals Cr in water solution, a series of potassium bichromate standard solutions were prepared in the lab. The characteristic line intensity of Cromium (Cr) element at 357.87, 359.35, 360.53, 425.43, 427.48, and 428.97 nm was taken to build up the correlation with concentration. The indexes of relative standard deviation, intercept, slope, R ² (coefficient of determination), and root mean square error of calibration were selected to verify the precision and accuracy of models. The comprehensive results showed that the 425.43 nm line had better superiority than other lines. And the detection limit of 6 ug/ml and repeatability of 3 % are reported. To improve the model accuracy further, the intensity ratio of single 425.43 nm line to the whole spectrum was extracted. And a linear relationship between the intensity ratio and the element Cr concentration was constructed. The results demonstrated the intensity ratio calibration had better accuracy than single line calibration, especially after smoothing. To verify the accuracy of prediction, the 100 ug/ml concentration sample was used as prediction sample. The relative error values are 13.2, 11.7, and 10.8 % for single line calibration, intensity ratio calibration with raw data, and by use of smooth processing data, respectively. The results further indicated that the intensity ratio calibration improved the accuracy of measurement than single line calibration. It is worth mentioning that the application of LIBS aiming the direct analysis of heavy metals in water is a great challenge that still needs efforts for its development and validation.     

Broadband surface electromagnetic wave spectroscopy

Broadband generation and spectroscopic detection of infrared surface electromagnetic waves (SEW's) are reported from 600 to 1800 cm^?1. For KReO₄ coated metal samples a sharp absorption line near 1000 cm^?1 is used to compare the SEW and surface reflection spectroscopy (SRS) techniques. The integrated optical density of the absorption line is an order of magnitude larger with SEW spectroscopy than with SRS.     

利用一维Vlasov和Maxwell方程模拟激光等离子体相互作用

应用一维Vlasov和Maxwell耦合程序详细研究了激光等离子体相互作用中的基本问题——受激拉曼散射(SRS). 通过研究发现, SRS的产生与电子速度分布函数在相空间中的结构密切相关, 当电子速度分布函数形成相空间涡旋时,背向SRS光大幅增加,而当电子等离子体波相速度附近的电子速度分布函数曲线变平坦后, 背向SRS光基本停止发生. 在模拟中观测到了SRS的爆发、电子速度分布函数形成相空间涡旋、电子俘获等清晰的物理图像. 关键词： Vlasov-Maxwell模拟 受激拉曼散射