High Repetition Rate Laser-ablation Research Articles

Accurate elemental analysis of alloy samples with high repetition rate laser-ablation spark-induced breakdown spectroscopy coupled with particle swarm optimization-extreme learning machine

High repetition rate laser-ablation spark-induced breakdown spectroscopy (HRR LA-SIBS) coupled with particle swarm optimization-extreme learning machine (PSO-ELM) was developed to realize quantitative elemental analysis of aluminum alloy accurately. A compact Nd: YAG laser operated at 1 kHz was used as the ablation laser and a spark discharge was utilized to enhance the plasma emission. The characteristic lines of the elements were selected as input variables and the parameters of ELM were optimized by the PSO algorithm. The PSO-ELM calibration models were established. The correlation coefficient of prediction set reached to 0.9996, 0.9972 and 0.9999, the root mean square error of prediction set decreased to 0.0138%, 0.0045% and 0.0095% for Mg, Cr, and Cu analysis, respectively. Better predictive performance has been demonstrated in comparison with the univariate and SVM methods. HRR LA-SIBS coupled with PSO-ELM can give convenient, rapid and accurate elemental analysis of alloy samples. Moreover, it will extend the potential applications of HRR LA-SIBS in intelligent manufacturing and on-line monitoring in the future.

Quantitative elemental analysis of aluminum alloys with one-point calibration high repetition rate laser-ablation spark-induced breakdown spectroscopy

A one-point calibration method has been successfully used to improve the analytical accuracy of the calibration free HRR LA-SIBS technique.

Quantitative analysis of trace elements in bismuth brass with high repetition rate laser-ablation spark-induced breakdown spectrum

Bismuth brass has very good mechanical properties and is friendly to environment. Therefore, it can be widely used in different fields. In order to realize the convenient, rapid and sensitive elemental analysis of trace elements in bismuth brass, fiber laser based high repetition rate laser-ablation spark-induced breakdown spectroscopy (HRR LA-SIBS) is developed. In the experiments, a compact fiber laser operated at 5 kHz pulse repetition rate is used to ablate the sample and produce plasma, and the spark discharge is used to further break down the ablated sample and enhance the plasma emission for sensitive elemental analysis. A compact fiber-optic spectrometer coupled with non-intensified charge-coupled device (CCD) is used to record the spectra. Bismuth, lead and tin in several bismuth brass standard samples are quantitatively analyzed. The plasma temperature is determined to be about 7962 ± 300 K by using the Boltzmann plots of copper, zinc and tin elements; the electron density is determined to be about 1.049 × 10<sup>–17</sup> cm<sup>–3</sup> based on the Stark broadening of Cu (I) 510.47 nm analytical line. The plasma is determined to be in local thermodynamic equilibrium (LTE) state according to McWhirter criterion as well as appended criteria for transient plasma. Under the present experimental condition, the calibration curves of bismuth, lead and tin in bismuth brass are built with fitting goodness of higher than 95%. The detection limits of bismuth, lead and tin are determined to be 25.5 ppm, 64.2 ppm and 316.5 ppm, respectively. The weak transition probability of tin atoms leads to worse detection limit of tin than the scenarios of bismuth and lead. The ways to further improve the analytical sensitivity and minimize system dimensions are discussed in this article. It is demonstrated that high repetition rate laser-ablation spark-induced breakdown spectrometer based on compact fiber laser as well as compact fiber-optic spectrometer can be used to realize the convenient, rapid and sensitive elemental analysis of trace elements in bismuth brass. This study is also helpful in analyzing the trace harmful elements, including bismuth, lead and tin in high temperature alloys with HRR LA-SIBS. In comparison with laser-induced breakdown spectroscopy (LIBS), the HRR LA-SIBS technique has several intrinsic advantages, such as fast spectral data collection speed, cost-effective system and low continuum background and so on. This technique is very useful in implementing the elemental analysis of different alloy samples and can be potentially used in metallurgical industry in the future.

Application of calibration-free high repetition rate laser-ablation spark-induced breakdown spectroscopy for the quantitative elemental analysis of a silver alloy.

In this work, we report the application of a calibration-free (CF) method combined with high repetition rate laser-ablation spark-induced breakdown spectroscopy (HRR LA-SIBS) to the analysis of a silver alloy. The sample was ablated by a fiber laser operated at a 30 kHz pulse repetition rate, and a spark discharge was applied to enhance plasma emission. Electron number density and plasma temperature were estimated using Stark broadening of spectral lines and the Saha-Boltzmann plot method, respectively. The fulfillment of the local thermodynamic equilibrium (LTE) approximation of the measurement was verified. Averaged electron density and plasma temperature were calculated as 1.11×1017cm-3 and 7355 K, respectively. The elemental composition of a silver alloy sample was determined, and the result was compared with that analyzed with inductively coupled plasma optical emission spectrometry (ICP-OES). The analytical error was within a 15% range. It was demonstrated that the CF HRR LA-SIBS technique could potentially provide elemental analysis for silver alloys without requiring a standard sample.

Application of fiber optic high repetition rate laser-ablation spark-induced breakdown spectroscopy on the elemental analysis of aluminum alloys.

Fiber optic high repetition rate laser-ablation spark-induced breakdown spectroscopy was applied to realize elemental analysis of aluminum alloys. A compact fiber laser was used as source of laser-ablation and spark discharge was used to enhance the atomic emission of the laser-induced plasma. Plasma emission spectra were recorded with a compact fiber spectrometer in a nongated signal recording mode. Calibration curves of Cr, Cu, Mn, Mg, and Zn in aluminum alloys were built under appropriate experimental conditions and the detection limits of these elements were determined to be 4.4, 5.6, 4.9, 8.3, and 31.1 ppm, respectively. Compared to those obtained in fiber optic high repetition rate laser-induced breakdown spectroscopy using the same fiber laser, a 3-18 improvement factor in the detection limit has been demonstrated. This system is compact and cost effective, and the technique can be applied to rapid and convenient element analysis of different alloy samples.

Calibration-free elemental analysis combined with high repetition rate laser-ablation spark-induced breakdown spectroscopy

Calibration-free (CF) method combined with high repetition rate laser-ablation spark-induced breakdown spectroscopy (HRR LA-SIBS) was first utilized to realize elemental analysis of alloy samples. A compact fiber laser operated at 30 kHz pulse repetition rate was used to ablate the sample and the spectra were recorded with a compact fiber spectrometer in non-gated signal recording mode. Three standard aluminum alloy samples were analyzed to evaluate the performance of this technique. Median filtering method was applied to reduce the contribution of the continuum background to the intensity of the atomic lines. The averaged electron density was determined to be (2.36–2.49) × 1017 cm−3 according to the Stark broadening of four ionic lines. 11,800 K averaged plasma temperature was estimated from the Saha-Boltzmann plots. The plasma could be verified to be in a state close to local thermodynamic equilibrium. The analytical error was <0.5% for the major element and <35% for minor elements with >0.1% concentrations. It was demonstrated that CF method combined with HRR LA-SIBS was possible to realize reliable quantitative elemental analysis for aluminum alloy samples.

Sensitive elemental analysis with high repetition rate laser-ablation spark-induced breakdown spectroscopy combined with lock-in signal detection

High repetition rate laser-ablation spark-induced breakdown spectroscopy (HRR LA-SIBS) combined with lock-in signal detection was developed to realize sensitive trace elements analysis. In order to realize the lock-in signal detection, the repetition rate of laser pulses was increased to 4 kHz and the time duration of the plasma emission was prolonged to be about 10 microseconds by the spark discharge, thus the duty cycle has been increased to 4% approximately. The influence of the continuum background of the plasma emission to the signal detection was reduced with a gated preamplifier. Trace lead and aluminum in brass samples and trace chromium and manganese in aluminum alloy samples were analyzed experimentally. The detection limits of them were estimated to be about 112, 178, 235 and 202 ppb under current experimental condition, demonstrating an obvious improvement on the analytical sensitivity of this technique comparing with conventional single pulse laser-induced breakdown spectroscopy. The HRR LA-SIBS technique combined with lock-in signal detection can be potentially applied to realize direct and sensitive elemental analysis of different solid samples.

Elemental analysis of copper alloy by high repetition rate LA-SIBS using compact fiber spectrometer

High repetition rate laser-ablation spark-induced breakdown spectroscopy (HRR LA-SIBS) was first used to analyze trace elements in copper alloy samples. The 1064 nm output of an acousto-optically Q-switched Nd:YAG laser operated at a pulse repetition rate of 1 kHz was utilized to ablate copper alloy and to form original plasma, spark-discharge was applied to further breakdown the ablated samples and enhance the emission of the laser-induced plasma. A compact multichannel fiber spectrometer was used to analyze the plasma emission under non-gated operation mode. Under the assistance of high repetition rate spark discharge, the plasma emission was able to be improved significantly. The determined limits of the detection of lead and aluminum were 15.5 ppm and 1.9 ppm by HRR LA-SIBS, respectively, which were 11 and 6 folds better than that determined by HRR LIBS under the same laser-ablation condition. This work demonstrates the feasibility of using fiber spectrometer to analyze plasma emission under non-gated operation mode and the possibility of building a portable HRR LA-SIBS system for rapid elemental analysis of copper alloys and other solid samples.

Analysis of magnesium and copper in aluminum alloys with high repetition rate laser-ablation spark-induced breakdown spectroscopy

In order to improve the analytical speed and performance of laser-ablation based atomic emission spectroscopy, high repetition rate laser-ablation spark-induced breakdown spectroscopy (HRR LA-SIBS) was first developed. Magnesium and copper in aluminum alloys were analyzed with this technique. In the experiments, the fundamental output of an acousto-optically Q-switched Nd:YAG laser operated at 1 kHz repetition rate with low pulse energy and ~120 ns pulse width was used to ablate the samples and the plasma emission was enhanced by spark discharge. The spectra were recorded with a compact fiber spectrometer with non-intensified charge-coupled device in non-gating mode. Different parameters relative with analytical performance, such as capacitance, voltage, laser pulse energy were optimized. Under current experimental conditions, calibration curves of magnesium and copper in aluminum alloys were built and limits of detection of them were determined to be 14.0 and 9.9 ppm by HRR LA-SIBS, respectively, which were 8–12 folds better than that achieved by HRR LA under similar experimental condition without spark discharge. The analytical sensitivities are close to those obtained with conventional LIBS but with improved analytical speed as well as possibility of using compact fiber spectrometer. Under high repetition rate operation, the noise level can be decreased and the analytical reproducibility can be improved obviously by averaging multiple measurements within short time. High repetition rate operation of laser-ablation spark-induced breakdown spectroscopy is very helpful for improving analytical speed. It is possible to find applications in fast elements analysis, especially fast two-dimension elemental mapping of solid samples.

Laser fluence, repetition rate and pulse duration effects on paint ablation

The efficiency (mm 3/(J pulse)) of laser ablation of paint was investigated with nanosecond pulsed Nd:YAG lasers ( λ = 532 nm) as a function of the following laser beam parameters: pulse repetition rate (1–10,000 Hz), laser fluence (0.1–5 J/cm 2) and pulse duration (5 ns and 100 ns). In our study, the best ablation efficiency ( η ≅ 0.3 mm 3/J) was obtained with the highest repetition rate (10 kHz) at the fluence F = 1.5 J/cm 2. This ablation efficiency can be associated with heat accumulation at high repetition rate, which leads to the ablation threshold decrease. Despite the low thermal diffusivity and the low optical absorption of the paint (thermal confinement regime), the ablation threshold fluence was found to depend on the pulse duration. At high laser fluence, the ablation efficiency was lower for 5 ns pulse duration than for the one of 100 ns. This difference in efficiency is probably due to a high absorption of the laser beam by the ejected matter or the plasma at high laser intensity. Accumulation of particles at high repetition rate laser ablation and surface shielding was studied by high speed imaging.