PhD Defense by Eirini Malegiannaki
Title: Laser ablation for water isotopic analysis with particular focus in spectral estimation for diffusion studies
Abstract:
This thesis presents a novel ice core sampling technique specifically designed for water isotope analysis, by coupling Laser Ablation (LA) with Cavity Ring Down Spectroscopy (CRDS). The micro-destructive nature of LA allows for high spatial resolution and minimal sample usage, addressing the challenges of achieving high accuracy and precision in water isotope measurements from the extremely thin layers at the base of deep ice cores, such as the one obtained from the Beyond EPICA - Oldest Ice Core project.
Two different laser ablation systems were employed in this study. The first system is a custom-made setup dedicated to water isotope studies in ice cores, while the second system uses a commercial LA setup coupled with a CRDS analyzer, serving as a proof of concept of the proposed method.
The first system comprises a femtosecond (fs) laser operating at 1030 nm with an open-design ablation chamber capable of scanning ice core samples up to 55 cm in length. This system was initially designed at the Physics of Ice, Climate, and Earth (PICE) - University of Copenhagen, and its development has been further advanced as part of this thesis. Test measurements were conducted on all critical components contributing to the functionality of a future LA-CRDS system, including laser focusing, gas flow dynamics, and ablation chamber design, along with detailed crater characterization to enhance understanding of the ablation process in ice. These tests provide initial insights into the system’s ablation performance.
The second system is a commercial laser ablation setup that consists of an ArF nanosecond (ns) laser operating at 193 nm and an integrated closed-design two- volume ablation chamber accommodating samples up to 5 cm in length. The ns LA system was coupled with a CRDS water isotopic analyzer at Ca’ Foscari University of Venice, achieving a resolution of 0.4 cm along the ice core depth in a discrete mode through raster scanning and further tested on ice standards and ice core samples.
Although LA-CRDS is still in the development stage for high-resolution water isotope measurements in ice cores, this study establishes foundational concepts and defines pathways for further research aiming at continuous, high-resolution isotopic analysis of long ice core records. Once fully operational, this method could provide a promising alternative to traditional continuous flow techniques that rely on melting and vaporizing ice samples. Ultimately, the LA-CRDS approach will facilitate the study of diffusion processes and improve temperature reconstructions, particularly for deep ice cores.
Evaluation Committee: Associate Professor Aslak Grinsted (chair), Professor Wolfgang Müller, Associate Professor Yang Zhang
Supervisors: Associate Professor Vasileios Gkinis, Professor Dorthe Dahl-Jensen, Professor Carlo Barbante