טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentKrasniker Rivka
SubjectEnvironmental Analysis by Laser Induced Breakdown
Spectroscopy
DepartmentDepartment of Chemistry
Supervisor Professor Israel Schechter


Abstract

We developed and applied the Laser Induced Breakdown Spectroscopy (LIBS) technique for fast and sensitive monitoring of hazardous elements in solids. The method is based on spectral analysis of the plasma formed by a focused laser pulse. This method has both on-line and in-situ capabilities and results may be obtained within seconds, without any sample preparation. Our main problems were related to considerable signal variations and to matrix effects, which actually limited the detection limits.

We introduced a new experimental setup to handle the above problems. Our method was based upon the idea that morphological information of a single plasma event may be applied for plasma characterization. Morphological information was obtained by simultaneous spatial and temporal resolution of the laser plume. Thus, a new multifiber imaging spectrometer, coupled with an ICCD detection system, was developed. A special sample holder, which enabled simultaneous observation of single-shot plasmas through eight optical fibers, was constructed. The fibers collected the emission at several locations from single-shot plasma, perpendicularly to its expansion axis. This setup was shown to provide the required insight into the plasma dynamics, which was necessary for understanding the nature of the fluctuations and finally for their compensation.

Our new experimental setup was applied to the investigation of matrix effects in LIBS analysis. Results on analysis of Pb in natural soils, using this setup, were reported. The origin of analytical matrix effects was also investigated. A simple experimental setup for estimating the energy coupled in the plasma was designed and applied to this task. Finally, we suggested a low-cost setup that may replace the expensive gated detectors, while maintaining acceptable analytical performance. The proposed setup was a result of the investigation of the plasma-front propagation in LIBS analysis.