PhD defence by Doyinsola S. Sonoiki

Abstract

Light can reveal the secrets of matter. Laser spectroscopy harnesses this power to analyze materials in real time, transforming industries from environmental monitoring to food quality control. This PhD thesis, titled “Supercontinuum Laser Spectroscopy”, explores two spectroscopy techniques that integrate cutting-edge lasers to advance the field of analytical spectroscopy, the science that reveals the composition of matter through light.

The first part of the thesis focuses on supercontinuum lasers – special light sources that combine the brightness of lasers with the broad color range of white light. We used this in infrared absorption spectroscopy for food quality control analysis. We demonstrated a novel approach to building a single-path configuration measurement system using a supercontinuum laser, enabling simultaneous measurement of the near- and mid-infrared regions in transmission and attenuated total reflectance (ATR) modes. This work addresses the long-standing challenge of combining the two regions with a single instrument for the analysis of aqueous samples, given substantial differences in optical material transparency and molar absorptivity. This novel approach can improve prediction accuracy, enabling a more robust method for analyzing aqueous samples.

In the second part, Laser-Induced Breakdown Spectroscopy (LIBS) was used to analyze marine protective coatings. We applied LIBS in a new way – as a real-time monitor during laser cleaning of marine protective coatings. Protective coatings are key in the marine industry for protecting marine structures from harsh environmental conditions, including corrosion and fouling. For good maintenance, the protective coating needs to be reapplied consistently, which means worn-out coating will be removed before a new one is applied. Compared to existing techniques like high-medium blasting, laser ablation technique produces less waste and less pollution to the environment. Here, LIBS is used to characterize coating layers during cleaning process of worn-out coating to determine their composition and the total time required to remove all layers without damaging the marine structure. This work contributes to a clean, waste-free alternative for removing degraded coatings to support material recycling and analysis, supporting more sustainable maintenance of marine structures and the environment.

In short, this thesis demonstrates how advanced laser-based techniques can make material analysis faster, cleaner, and more accurate – whether for ensuring food quality or maintaining marine infrastructure.

Supervisors

• Principal supervisor: Senior Researcher, Christian Rosenberg Petersen, DTU Electro
• Co-supervisor: Professor, Ole Bang,  DTU Electro 

Evaluation Board

• Examiner: Chief consultant, Maria Knadel, Dept of Agroecology, Aarhus University, DK
• Examiner: Associate Professor, Simona Cristescu, Nijmegen, NL

Chairman

• Senior Researcher, Lars René Lindvold, Department of Electrical and Photonics Engineering, DTU

Master of the Ceremony

• TBA, Department of Electrical and Photonics Engineering, DTU