Laser-Induced Plasma Lifetime and Emission Spectrum Modeling : Generating Simulated Spectral Data for Neural Network Training
Ojanen, Eetu (2026)
2026
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Julkaisun pysyvä osoite on
https://urn.fi/URN:NBN:fi:amk-202604207071
https://urn.fi/URN:NBN:fi:amk-202604207071
Tiivistelmä
This thesis examined how simulated laser-induced breakdown spectroscopy (LIBS) spectra could be made comparable to experimentally measured time-integrated spectra. The objective was to develop a practical framework for generating simulated exposure spectra and to evaluate how well such spectra reproduced measured LIBS spectra under a simplified plasma model.
The study was carried out as an article-based thesis consisting of two included works and a synthesis chapter. A GPU-accelerated forward model was used to calculate optically thin local thermodynamic equilibrium (LTE) snapshot spectra for successive plasma states defined by parameterized temperature and electron density decay functions. Time-integrated spectra were then produced by summing the simulated snapshot spectra over the selected exposure window. Measured spectra were preprocessed by dark-noise subtraction, baseline removal, wavelength alignment, and normalization before comparison. The similarity between measured and simulated spectra was evaluated using mean absolute error (MAE), mean squared error (MSE), and the spectral angle. Cooling and electron density decay trajectories were explored using a Monte Carlo-type search.
The results showed that the simulated spectra reproduced many line positions and some broader spectral features, but the agreement with the measured spectra remained limited. The main discrepancies were observed in peak intensities, line ratios, line shapes, and peaks that were present in the measurements but absent from the simulations. No single uniquely optimal cooling and electron density decay behaviour was identified; instead, several case-specific parameter combinations produced similarly good matches within the selected model and metric framework.
It was concluded that time-integrated LIBS spectra can be simulated in a practical way by summing successive optically thin LTE snapshot spectra along parameterized plasma-evolution trajectories. However, the fitted plasma parameters should be interpreted as apparent best-fit quantities within the model rather than as unique true plasma conditions. The thesis provides a useful optically thin LTE reference case for exposure-spectrum fitting and clarifies both the usefulness and the limitations of this simplified modelling approach.
The study was carried out as an article-based thesis consisting of two included works and a synthesis chapter. A GPU-accelerated forward model was used to calculate optically thin local thermodynamic equilibrium (LTE) snapshot spectra for successive plasma states defined by parameterized temperature and electron density decay functions. Time-integrated spectra were then produced by summing the simulated snapshot spectra over the selected exposure window. Measured spectra were preprocessed by dark-noise subtraction, baseline removal, wavelength alignment, and normalization before comparison. The similarity between measured and simulated spectra was evaluated using mean absolute error (MAE), mean squared error (MSE), and the spectral angle. Cooling and electron density decay trajectories were explored using a Monte Carlo-type search.
The results showed that the simulated spectra reproduced many line positions and some broader spectral features, but the agreement with the measured spectra remained limited. The main discrepancies were observed in peak intensities, line ratios, line shapes, and peaks that were present in the measurements but absent from the simulations. No single uniquely optimal cooling and electron density decay behaviour was identified; instead, several case-specific parameter combinations produced similarly good matches within the selected model and metric framework.
It was concluded that time-integrated LIBS spectra can be simulated in a practical way by summing successive optically thin LTE snapshot spectra along parameterized plasma-evolution trajectories. However, the fitted plasma parameters should be interpreted as apparent best-fit quantities within the model rather than as unique true plasma conditions. The thesis provides a useful optically thin LTE reference case for exposure-spectrum fitting and clarifies both the usefulness and the limitations of this simplified modelling approach.