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Abstract

Spall failure in materials occurs when shockwaves, propagating through a material, interact leading to failure once the generated hydrostatic tensile stress exceeds the material’s strength. In this thesis, a novel femtosecond two-pulse laser approach is introduced where the front and back surface of a material is simultaneously illuminated. By comparing this method to the conventional single-pulse approach, the unique effects of introducing a secondary laser pulse are demonstrated on thin Nickel foils and commercially available alumina. Experimental observations using electron microscopy, X-ray tomography, and focused ion beam milling revealed that the proposed approach effectively induces failure at specific locations in the sample, away from the free surfaces. Notably, the two-pulse approach significantly reduces the laser fluence spall threshold compared to the single-pulse method. For instance, while the single-pulse method required a fluence threshold of 2,500 J · m⁻², the two-pulse approach achieved spallation at 1,750 J · m⁻², high- lighting its ability to generate higher hydrostatic stress with lower energy input. Similarly, alumina samples exhibited spallation under the two-pulse approach at a fluence of 600 J · m⁻², compared to 1,800 J · m⁻² for the single- pulse method, despite the two-pulse samples generating fewer voids. Prior to failure, molecular dynamics (MD) simulations highlighted the ductile failure in Nickel, and brittle failure in alumina. As these findings suggested the potential of the proposed approach to generate large hydrostatic tensile stress, a comprehensive MD study was conducted on single-crystalline Nickel to understand the effects of controllable parameters on material behaviour by tracking their influence on the different types of laser-inducing mechanisms. Furthermore, as experimental results confirmed that the two-pulse approach induces spallation at the sample center, similar to conventional plate-impact methods. These findings demonstrate that the two-pulse laser spallation approach offers a powerful and efficient method for high-throughput spallation experiments, enabling the generation of extreme strain rates and hydrostatic tensile stresses with reduced energy input. Lastly, a key outcome of this research is the development and implementation of the first femtosecond laser shock facility in Western Canada, providing a new platform for investigating laser-induced shock dynamics.