Oily soil is harmful to the environment, and heavy metals therein may cause hazards to human health. A rapid detection method for heavy metals in oily soil is needed to provide accurate data support for in situ soil pollution assessment and restoration. In the present study, a laser-induced breakdown spectroscopy (LIBS) technique combined with interval partial least squares (IPLS) was proposed to determine Cu, Zn, Cr and Ni in oily soil samples. In order to obtain a good IPLS model, the full spectrum was divided into 10, 20, 30, 40, 50, 60, 70, 80 and 90 subintervals for IPLS model optimization. The results show that the 30th subinterval from an 80-interval case has the lowest RMSE and the best R². Compared to the PLS model using the full spectrum, the IPLS model with the 30th subinterval from the 80-interval case as the input variable has higher R²s and lower RMSEs for Cu, Zn, Cr and Ni. The R² was improved from 0.96 to 0.99, and the RMSE was reduced from 0.03 to 0.01. The calculation speed was increased by about 5 times. The LIBS technique coupled with the IPLS method can quickly and effectively realize the quantitative analysis of heavy metals in oily soil and can even be used for the analysis and control of soil pollution.

Laser-induced breakdown spectroscopy (LIBS) is a rapid and simple analytical method that provides qualitative and quantitative elemental information of samples without damaging them and does not require any sample preparation. Recently, an increasing number of studies have used LIBS to detect aerosols. This technique meets the requirements to be used in some practical applications, such as atmospheric monitoring and industrial processes. However, the unique properties of aerosols bring a level of uncertainty to the LIBS signals of the samples, which is an obstacle to overcome. This review attempts to summarize the relevant research regarding aerosol-LIBS, including the various apparatuses, conditional analysis methods, effects of plasma–particle interactions, means for improving signal intensity, and applications.

This work explores the combination of LIBS technology and K-ELM algorithm for the quantitative analysis of total iron (TFe) content and alkalinity of sinter.

Potash is the main raw material for the production of agricultural fertilizers. Herein, random forest (RF) models fusing variable importance and wavelet transform were proposed to determine the K content in a potassic salt ore. Specifically, 53 potassic salts samples were analyzed, of which 37 were treated as the calibration set. An original RF model was developed for regression with the optimized parameters n_tree and m_try. However, R_P2 (0.7399) and the modeling time (251.8 s) of the RF model were not satisfactory. Thus, we initially explored the effect of different variable importance (VI) thresholds on the quantitative results. When the VI threshold was set to 0.090, the variable number of the VIRF model was reduced from 27 620 to 3355. There were no significant improvements for VIRF in the other model performance parameters such as RMSE_P and R_P ². Then, wavelet transform was adopted to screen the input variables of the RF model (defined as WTRF). Their promotion ratios were 16% (R_P ² from 0.7399 to 0.8555), 38% (RMSE_P from 0.1798 to 0.1106), 62% (MRE from 0.2740 to 0.1032), and 11% (MRSD from 0.0686 to 0.0613). In the case of modeling time, it was promoted by about three orders of magnitude. Upon further using the variable importance for the WTRF model (defined as WT-VIRF), because all the selected input variables filtered by wavelet transform contributed significantly to the quantitative results, no more variables were removed and then, the WT-VIRF model achieved the exact result with the WTRF model. Thus, all the results demonstrate that the RF model combined with WT is a promising methodology for the quantitative analysis of the K content in potassic salt ores.

We report, to the best of our knowledge, the first visible-wavelength all-fiber passively mode-locked vortex laser by a figure-9 cavity in combination with $\sim$ 635 nm mode selective coupler, which can deliver picosecond optical vortex pulses with topological charges of OAM $_{\pm 1}$ . The mode-locked vortex laser emits stable rectangular pulses with pulse duration tunable range from 85 to 510 ps and a 0.16-nm narrow linewidth at 634.36 nm. The maximum output power of the vortex laser reaches 1.3 mW with a high purity $\sim 97.2\%$ . This work demonstrated the generation of picosecond pulsed vortex in visible passively mode-locked fiber laser, showing their potential for applications in particle trapping, optical tweezers, and high-resolution microscopy.