Novel Applications of Laser-Induced Breakdown Spectroscopy

In situ diagnosis of mature HLB-asymptomatic citrus fruits by laser-induced breakdown spectroscopy

Laser-induced breakdown spectroscopy (LIBS) is a promising alternative to conventional methods in classifying citrus huanglongbing (HLB). Mature citrus fruits with similar features were picked and divided into healthy and HLB-asymptomatic groups. LIBS spectra and images were collected by focusing a laser on fresh fruit surfaces without sample preparation. The pH value and soluble solids content of juice as the indicators of acidity and sugar were detected, and the content of Ca, Zn, and K in peel and pulp was analyzed. The characteristic lines from LIBS spectra were extracted by continuous wavelet transform and principal component analysis (PCA). The t-test of these indicators displayed significant difference between the two groups. Fisher discriminant analysis and multilayer perception neural network (MLP) were applied to identify the disease. The classification accuracy reached 100% by PCA-MLP. The results show that LIBS can realize in situ detection of citrus HLB fruits.

Detection of Gadolinium in Surrogate Nuclear Fuel Debris Using Fiber-Optic Laser-Induced Breakdown Spectroscopy under Gamma Irradiation

Fiber-optic laser-induced breakdown spectroscopy (FO-LIBS) was applied to a qualitative and quantitative analysis of gadolinium (Gd) in mixed oxide samples, simulating nuclear fuel debris in the damaged reactors of the Fukushima Daiichi Nuclear Power Station. The surrogate debris was prepared from mixed oxide materials containing Gd2O3, with varying Gd concentrations. The emission spectra of the surrogate debris show that the optical emission lines at 501.5 nm and 510.3 nm are suitable for Gd detection in the nuclear fuel debris. LIBS measurements were further performed under gamma irradiation (0–10 kGy/h), resulting in a decrease in spectral intensities due to radiation-induced damage to the optical fiber. For quantification of Gd, robust calibration curves against gamma irradiation were established from the intensity ratio of Gd (501.5 nm)/Ce (474.5 nm) emission lines, yielding the limits of detection for Gd in the range of 0.03–0.08 wt%. These results demonstrate that FO-LIBS is a potential tool for in situ and remote analysis of nuclear fuel debris.

Accuracy enhancement of laser induced breakdown spectroscopy by safely low-power discharge

Improvement in detection accuracy is an important and hot topic for laser induced breakdown spectroscopy (LIBS). Discharged-pulse assisted (DPA) plasma has been investigated as an effective way to enhance analytical capabilities and accuracy of LIBS. Most of reported DPA experiments have been performed using high voltage and power to comprehend spectrum enhancement. For safety concerns and maneuverability of LIBS equipment; low power and small current discharge are viable for industrial application. In this paper, the enhanced spectra with many extra peaks and higher line intensities were also detected, realized by a low-power discharge assisted LIBS (Max. 2.8 kV and ~1 mA), which are much lower than reported in literature ~MW discharge. The number of atomic peaks of the sample increases, on the other hand, and gradual peaks become stronger with the increase of discharged HV from 1 kV to 1.5 kV, 1.75 kV, 2 kV, 2.5 kV and 2.8 kV. The discharge current increases from 0.2 mA to 1.5 mA, which is almost threshold discharge voltage. After processing, the original spectra, including the peak shift and peak correction by statistics and physics, resulted in achievement of better line stability in terms of relative standard deviation (RSD) of ash, carbon, and volatile coal samples with root mean square error prediction (RMSEP) of 0.4864, 0.3682, 0.3374 and the linear regression coefficient R² = 0.99, 0.99,0.98, respectively. The result proposes a promising method to improve detection accuracy of LIBS with simple setup, high safety and low-cost.