Master Thesis defense by Ioanna Bertsia-Kanatouri

Title: Towards quasi-non-destructive water isotope ratio measurements in ice cores using femtosecond laser ablation

Abstract: 
Laser ablation is a promising technique for the analysis of water isotopes in deep and old ice cores. Projects such as the Beyond EPICA initiative aim to recover ice exceeding 1.2 Myr in age, where annual layers become increasingly compressed with depth. This makes high spatial resolution and minimal sample consumption essential for resolving climatic information while preserving valuable material. Femtosecond laser ablation offers significant advantages due to its minimally destructive nature and cold ablation regime, enabling sub-millimetre-scale sampling while reducing thermal alteration of the ice.

This thesis presents the development and characterisation of a custom-built laser ablation system at the Niels Bohr Institute. Synthetic ice cores are used to evaluate the stability and reproducibility of the ablation process under varying irradiation conditions. The system allows samples up to 55 cm in length to be analysed under atmospheric pressure and dry-air conditions, with in situ imaging and automated long-duration measurement sequences. Individual experimental runs can consist of up to 400 consecutively produced craters, generated through iterative laser positioning across the sample surface.

Crater analysis shows uniform morphology and systematic diameter growth with increasing exposure time. Typical mean crater diameters range from approximately 103 - 165 μm, depending on pulse number. The results indicate that ablation is not governed by a single threshold, but instead reflects a dynamic, pulse-dependent response consistent with incubation and saturation effects. Overall, the system demonstrates stable operation and reliable crater formation, forming a basis for future integration with cavity ring-down spectroscopy (CRDS) and subsequent validation of water isotope measurements.

Supervisors: Vasileios Gkinis, Robin Vinther Nielsen
Censor: Peter Balling (AU)