Laser-ablation Spark-induced Breakdown Spectroscopy And Its Application In Element Analysis Of Aluminum Alloys

Laser-induced breakdown spectroscopy(LIBS)is widely used in spectral analysis,but the analytical sensitivity of the traditional LIBS is usually low due to the strong bremsstrahlung emission of the electrons in the plasma.The scientists have tried several methods to enhance the signal intensity and improve the analytical sensitivity of LIBS.The technique used in this paper is one of them,which is called laser-ablation spark-induced breakdown spectroscopy(LA-SIBS).In this paper,the study of LA-SIBS was carried out at low repetition rate firstly.In the experiment,an electro-optically Q-switched Nd: YAG laser at 5 Hz repetition rate was used as the laser source,and a gate-able pulsed high-voltage power source was used as the power supplier of the spark discharge.It was proved that the LA-SIBS could be used to enhance the signal intensity and improve the analytical sensitivity.And the characteristics of discharge channel in LA-SIBS was also studied in detail.It was demonstrated that under suitable laser pulse energy and geometrical arrangement of the electrodes,it was possible to change the discharge channel from “V-shaped” type to parallel type by adjusting this time delay under external trigger mode.In the “V-shaped” discharge,the spark discharge was able to increase the diameters of the craters and deteriorate the lateral resolution.However,in the parallel discharge,the spark discharge did not increase the diameters of the craters ensuring that the spatial resolution in this technique was only determined by laser-ablation.Under the condition of parallel discharge,quantitative analysis of chromium in aluminum alloy with LA-SIBS was carried out and the limit of detection of chromium reached 8.8 ppm,which was 8 times better than that obtained in LIBS without the spark discharge.In order to improve the analytical speed of LIBS,it is necessary to utilizing the high repetition rate laser sources.However,the pulse energy of the lasers operated at high repetition rate is usually low which leading to low analytical sensitivity.In order to enhance the signal intensity of plasma radiation,an elements analysis system with LA-SIBS at high repetition rate was established,which could significantly improve the analytical speed and the analytical sensitivity of the system.In this paper,a HRR LA-SIBS spectral analysis system was established by using an acoustic-optically Q-switched Nd: YAG laser at 1 kHz repetition rate.It was demonstrated that the LA-SIBS can also work effectively at high repetition rate.Quantitative analysis of magnesium and copper in aluminum alloys with HRR LA-SIBS was carried out.And the effects of different parameters were studied to find the optimal experimental condition.The limits of detection of magnesium and copper in aluminum alloys were determined to be 14.0 and 9.9 ppm by HRR LA-SIBS,which were 8-12 folds better than that achieved by HRR LA.HRR LA-SIBS is very helpful for improving analytical speed,and by averaging multiple measurements within short time,the noise level can be decreased and the analytical reproducibility can be improved.It is possible to find applications in fast two-dimension elemental mapping of solid samples.