This study explores the application of laser-induced breakdown spectroscopy (LIBS) to classify steel samples, which gives a novel idea of utilizing the matrix effect.

Laser-induced breakdown spectroscopy (LIBS) is an analytical detection technique based on atomic emission spectroscopy to measure the elemental composition. LIBS has been extensively studied and developed due to the non-contact, fast response, high sensitivity, real-time and multi-elemental detection features. The development and applications of LIBS technique in Asia are summarized and discussed in this review paper. The researchers in Asia work on different aspects of the LIBS study in fundamentals, data processing and modeling, applications and instrumentations. According to the current research status, the challenges, opportunities and further development of LIBS technique in Asia are also evaluated to promote LIBS research and its applications.

A long–short double pulse laser-induced breakdown spectroscopy (long–short DP-LIBS) method was employed to improve the analytical performance of LIBS for the measurement of manganese in steel samples. The long pulse with a duration of 60 μs was generated using a neodymium-doped yttrium aluminum garnet (Nd:YAG) laser which was operated at free-running (FR) mode. To investigate the detection ability without sample preparation, the steel washers were tested using single-pulse LIBS (SP-LIBS) and long–short DP-LIBS, respectively. The measurement results show that long–short DP-LIBS was able to record clear spectra from the steel washers with a surface layer. Through the observation on the laser craters with a scanning electron microscope (SEM), the results suggest that the improvement in detection ability can be attributed to the pre-irradiation effect of long-pulse laser beam. Next, the analytical performance for quantitative measurement of manganese was evaluated employing ten standard steel samples. The results show that the linearity fit (R ² ) of the calibration curve is 0.988 for long–short DP-LIBS, whereas, R ² is only 0.810 for SP-LIBS under the same measurement conditions. The repeated measurement results show that the average relative standard deviation (RSD) of the tested samples is 29.3% for SP-LIBS and is 10.5% for long–short DP-LIBS. The prediction results also show that the average relative error of prediction (REP) is 94.9% for SP-LIBS and is 4.9% for long–short DP-LIBS.

Collinear long and short dual-pulse laser-induced breakdown spectroscopy (DP-LIBS) was employed to clarify the emission characteristics from laser-induced plasma. The plasma was sustained and became stable by the long pulse-width laser with the pulse width of 60 μs under free running (FR) conditions as an external energy source. Comparing the measurement results of stainless steel in air using single-pulse LIBS (SP-LIBS) and DP-LIBS, the emission intensity was markedly enhanced using DP-LIBS. The temperature of plasma induced by DP-LIBS was maintained at a higher temperature under different gate delay time and short pulse-width laser power conditions compared with those measured using short SP-LIBS. Moreover, the variation rates of plasma temperatures measured using DP-LIBS were also lower. The superior detection ability was verified by the measurement of aluminum sample in water. The spectra were clearly detected using DP-LIBS, whereas it cannot be identified using SP-LIBS of short and long pulse widths. The effects of gate delay time and short pulse-width laser power were also discussed. These results demonstrate the feasibility and enhanced detection ability of the proposed collinear long and short DP-LIBS method.

Laser-induced breakdown spectroscopy (LIBS) technology is an appealing technique compared with many other types of elemental analysis because of the fast response, high sensitivity, real-time, and noncontact features. One of the challenging targets of LIBS is the enhancement of the detection limit. In this study, the detection limit of gas-phase LIBS analysis has been improved by controlling the pressure and laser pulse width. In order to verify this method, low-pressure gas plasma was induced using nanosecond and picosecond lasers. The method was applied to the detection of Hg. The emission intensity ratio of the Hg atom to NO (I_Hg/ I_NO) was analyzed to evaluate the LIBS detection limit because the NO emission (interference signal) was formed during the plasma generation and cooling process of N₂ and O₂ in the air. It was demonstrated that the enhancement of I_Hg/ I_NO arose by decreasing the pressure to a few kilopascals, and the I_Hg/ I_NO of the picosecond breakdown was always much higher than that of the nanosecond breakdown at low buffer gas pressure. Enhancement of I_Hg/ I_NO increased more than 10 times at 700 Pa using picosecond laser with 35 ps pulse width. The detection limit was enhanced to 0.03 ppm (parts per million). We also saw that the spectra from the center and edge parts of plasma showed different features. Comparing the central spectra with the edge spectra, I_Hg/ I_NO of the edge spectra was higher than that of the central spectra using the picosecond laser breakdown process.