Heavy Metal Detection in Soils by Laser Induced Breakdown Spectroscopy Using Hemispherical Spatial Confinement

Spatial confinement has great potential for Laser Induced Breakdown Spectroscopy （LIBS） instruments after it has been proven that it has the ability to enhance the LIBS signal strength and repeatability. In order to achieve in-situ measurement of heavy metals in farmland soils by LIBS, a hemispherical spatial confinement device is designed and used to collect plasma spectra, in which the optical fibers directly collect the breakdown spectroscopy of the soil samples. This device could effectively increase the stability of the spectrum intensity of soil. It also has other advantages, such as ease of installation, and its small and compact size. The relationship between the spectrum intensity and the laser pulse energy is studied for this device. It is found that the breakdown threshold is 160 cm-2, and when the laser fluence increases to 250 J/cm2, the spectrum intensity reaches its maximum. Four different kinds of laser pulse energy were set up and in each case the limits of detection of Cd, Cu, Ni, Pb and Zn were calculated. The results show that when the laser pulse fluence was 2.12 GW/cm2, we obtained the smallest limits of detection of these heavy metals, which are all under 10 mg/kg. This device can satisfy the needs of heavy metal in-situ detection, and in the next step it will be integrated into a portable LIBS instrument.

Quantitative Analysis of Cr in Milk Powder by Laser Induced Breakdown Spectroscopy( LIBS)

At present, heavy metal pollution in food occurs frequently, which requires a novel method for rapid detection. Laser induced breakdown spectroscopy （LIBS） is a new technique for rapid and environmental friendly detection, but it lacks high sensitivity and stability which restrict its development. In this study, Cr-polluted infant milk powder was used as experimental material to explore the feasibility of the application of LIBS technique in food safety detection. Aiming at improving the precision and accuracy of Cr detection by LIBS technique, LIBS spectra of samples were collected by a spectrometer with an intensified charge-cou- pled device （ICCD） using three gratings with different resolutions to comprehensively compare and analyze the stability, sensitivity and quantitative analysis accura- cy of LIBS detection. The results showed that average relative standard deviation （RSD） of LIBS spectral intensity was below 10%, indicating good stability. LIBS signals were collected by three gratings for quantitative analysis, and the results demonstrated that the linear correlation coefficient R2 of fitting curves was 0. 248 87, 0.903 12 and 0.992 81, respectively; the relative errors between actual and predicted concentrations were 38.23%, 8.84% and 7.43%, respectively, indicating that gratings with higher resolutions could lead to higher linear correlation coefficient and better detection accuracy. According to the results, high-resolu- tion spectrometer could significantly improve the accuracy of LIBS detection of Cr concentration in milk powder, suggesting that it is feasible to detect heavy metals in food by LIBS technique with the improvement of core device performance.

Investigation of Laser Induced Breakdown Spectroscopy(LIBS)for the Differentiation of Nerve and Gland Tissue-A Possible Application for a Laser Surgery Feedback Control Mechanism

Laser surgery provides clean,fast and accurate modeling of tissue.However,the inability to determine what kind of tissue is being ablated at the bottom of the cut may lead to the iatrogenic damage of structures that were meant to be preserved.In this context,nerve preservation is one of the key challenges in any surgical procedure.One example is the treatment of parotid gland pathologies,where the facial nerve（N.VII） and its main branches run through and fan out inside the glands parenchyma.A feedback system that automatically stops the ablation to prevent nerve-tissue damage could greatly increase the applicability and safety of surgical laser systems.In the present study,Laser Induced Breakdown Spectroscopy（LIBS） is used to differentiate between nerve and gland tissue of an ex-vivo pig animal model.The LIBS results obtained in this preliminary experiment suggest that the measured spectra,containing atomic and molecular emissions,can be used to differentiate between the two tissue types.The measurements and differentiation were performed in open air and under normal stray light conditions.

Aqueous ruthenium detection by microwave-assisted laser-induced breakdown spectroscopy

Aqueous ruthenium was detected in real-time under ambient conditions using microwaveassisted laser-induced breakdown spectroscopy(MW-LIBS).A 10 mJ laser energy and 750 W microwave power were directed at an open liquid jet sample of ruthenium.It was observed that,for liquid flow,the coupling efficiency between the microwave and the laser-induced plasma was limited to 43%.The improvement in the ruthenium’s signal-to-noise ratio with MW-LIBS,with respect to LIBS,was 76-fold.Based on MW-LIBS,the limit of detection for aqueous ruthenium was determined to be 957±84 ppb.

Spectral Enhancement of Laser-Induced Breakdown Spectroscopy in External Magnetic Field

In this paper the spectral enhancement of laser-induced breakdown spectroscopy （LIBS） for copper plasma in the presence of a magnetic field is investigated and the temporal- and spatial-resolved plasma emission spectra are analyzed. Experimental results show that the copper plasma atomic and ion spectra have been enhanced in the presence of the external magnetic field. In addition, the Cu I 521.82 nm spectral intensity evolution with delay time appears to have a double peak around the delay time of 2 μs, but that of Cu II 507.57 nm has a sharp decrease because of the electron-atom three body recombination process. The plasma temperature with magnetic confinement is lower than that of the case in the absence of magnetic fields. Finally, the spectral enhancement mechanisms of laser induced breakdown spectroscopy with magnetic confinement are analyzed.

Evaluation of gases'molecular abundance ratio by fiber-optic laser-induced breakdown spectroscopy with a metal-assisted method

A metal-assisted method is proposed for the evaluation of gases’molecular abundance ratio in fiber-optic laser-induced breakdown spectroscopy(FO-LIBS).This method can reduce the laser ablation energy and make gas composition identification possible.The principle comes from the collision between the detected gases and the plasma produced by the laser ablation of the metal substrate.The interparticle collision in the plasma plume leads to gas molecules dissociating and sparking,which can be used to determine the gas composition.The quantitative relationship between spectral line intensity and molecular abundance ratio was developed over a large molecular abundance ratio range.The influence of laser ablation energy and substrate material on gas quantitative calibration measurement is also analyzed.The proposed metal-assisted method makes the measurement of gases’molecular abundance ratios possible with an FO-LIBS system.

Three-dimensionalization via control of laser-structuring parameters for high energy and high power lithium-ion battery under various operating con ditions

Laser-structuring is an effective method to promote ion diffusion and improve the performance of lithium-ion battery(LIB)electrodes.In this work,the effects of laser structuring parameters(groove pitch and depth)on the fundamental characteristics of LIB electrode,such as interfacial area,internal resistances,material loss and electrochemical performance,are investigated,LiNi_(0.5)Co_(0.2)Mn_(0.3)O_(2) cathodes were structured by a femtosecond laser by varying groove depth and pitch,which resulted in a material loss of 5%-14%and an increase of 140%-260%in the in terfacial area between electrode surface and electrolyte.It is shown that the importance of groove depth and pitch on the electrochemical performance(specific capacity and areal discharge capacity)of laser-structured electrode varies with current rates.Groove pitch is more im porta nt at low current rate but groove depth is at high curre nt rate.From the mapping of lithium concentration within the electrodes of varying groove depth and pitch by laser-induced breakdown spectroscopy,it is verified that the groove functions as a diffusion path for lithium ions.The ionic,electronic,and charge transfer resistances measured with symmetric and half cells showed that these internal resistances are differently affected by laser structuring parameters and the changes in porosity,ionic diffusion and electronic pathways.It is demonstrated that the laser structuring parameters for maximum electrode performance and minimum capacity loss should be determined in consideration of the main operating conditions of LIBs.

Monitoring the Laser Ablation Process of Paint Layers by PILA Technique

The spectrum analysis obtained by Fast Fourier Transform of the Photoacoustic In-duced by Laser Ablation (PILA) during laser assisted paints removal process is de-scribed, in order to identify the presence of paint components on a metallic surface, optimize the ablation rate and propose the method as a cleaning process monitoring. The process was carried out using a low-cost experimental setup which includes a burst-mode Nd:YAG laser, an electret microphone, an audio amplifier device and an oscilloscope, to record the acoustic pulse and analyze it. The samples surface mor-phology was characterized by Optical Microscopy and Optical Coherence Tomography (OCT) before and after irradiation to visualize the formation of craters. As additional monitoring technique, the Laser Induced Breakdown Spectroscopy (LIBS) was used. The potential of the analysis for qualitative monitoring of coating removal was demonstrated due to the coincidence of the information provided by LIBS and PILA techniques.

Laser ablation assisted spark induced breakdown spectroscopy and its application

Recently,laser ablation assisted spark induced breakdown spectroscopy(LA-SIBS)has been growing rapidly and continue to be extended to a broad range of materials analysis.Characterized by employ-ing a speifically designed high voltage and pulse discharge cireuit to generate a spark and used to enhance plasma emission produced by laser ablation,allows direct analysis of materials without prior sample preparation.This paper reviews recent development and application of laser ablation assisted spark induced breakdown spectrosoopy for material analysis.Following a summary of fundamentals and instrumentation of the LA-SIBS analytical techmique,the development and applications of laser ablation assisted spark induced breakdown spectroscopy for the analysis of conducting materials and insulating materials is described.

Temporal and spatial dynamics of optical emission from laser ablation of the first wall materials of fusion device

Laser-induced breakdown spectroscopy （LIBS） has been developed to in situ diagnose the chemical compositions of the first wall in the EAST tokamak. However, the dynamics of optical emission of the key plasma-facing materials, such as tungsten, molybdenum and graphite have not been investigated in a laser produced plasma （LPP） under vacuum. In this work, the temporal and spatial dynamics of optical emission were investigated using the spectrometer with ICCD. Plasma was produced by an Nd：YAG laser （1064 nm） with pulse duration of 6 ns. The results showed that the typical lifetime of LPP is less than 1.4 #s, and the lifetime of ions is shorter than atoms at ~10-6mbar. Temporal features of optical emission showed that the optimized delay times for collecting spectra are from 100 to 400 ns which depended on the corresponding species. For spatial distribution, the maximum LIBS spectral intensity in plasma plume is obtained in the region from 1.5 to 3.0 mm above the sample surface. Moreover, the plasma expansion velocity involving the different species in a multicomponent system was measured for obtaining the proper timing （gate delay time and gate width） of the maximum emission intensity and for understanding the plasma expansion mechanism. The order of expansion velocities for various species is Vc＋ 〉 VH 〉 Vsi＋ 〉 VLi 〉 VMo 〉 Vw. These results could be attributed to the plasma sheath acceleration and mass effect. In addition, an optimum signal-to-background ratio was investigated by varying both delay time and detecting position.

Spatial Resolution Measurements of C,Si and Mo Using LIBS for Diagnostics of Plasma Facing Materials in a Fusion Device

Recently, a laser-induced breakdown spectroscopic （LIBS） system has been developed for in situ measurements of the chemical compositions of plasma facing materials （PFMs） in the Experimental Advanced Superconducting Tokamak （EAST）. In this study, a LIBS system, which was used in a similar optical configuration to the in situ LIBS system in EAST, has been developed to investigate the spatial distribution of PFM elements at 10-4 Pa. The aim of this study was to understand the nature of the spatial distribution of atoms or ions of different elements in the plasma plume and optimize the signal to background ratio for the in situ LIBS diagnosis in EAST. The spatial profiles of the LIBS signals of C, Si, Mo and the continuous background were measured. Moreover, the influence of laser spot size and laser energy density on the LIBS signals of C, Si, Mo and H was also investigated. The results show that the distribution of the C, Si and Mo peaks＇ intensities first increased and then decreased from the center to the edge of the plasma plume. There was a maximum value at R ≈ 1.5 mm from the center of the plasma plume. This work aims to improve the understanding of ablating plasma dynamics in very low pressure environments and give guidance to optimize the LIBS system in the EAST device.

Control of molecular excitation during the plasma generation of a femtosecond laser pulse

From a classical dynamic simulation,we find the kinetic energy of the electrons generated during laser plasma generation depends on the laser polarization and intensity.The electron kinetic energy reaches its maximum with a fixed laser intensity for circularly polarized laser pulse.The fluorescence spectra at 380.4 nm from N2 and 391.3 nm from N2^＋ are measured;these are generated by both the direct excitation and electron collision excitation.The electron collision excitation is determined by the electron energy and reaches the maximal with a circularly polarized pulse.