Structure of the Plume Emitted during Laser Ablation of Materials

Laser ablation is a frequently used method of removing material from a solid surface by irradiating it with a powerful laser beam. It may be applied to machining materials, cleaning contaminated surfaces, deposition of thin coatings on surfaces etc. High energy, short duration laser pulse, focused on a small area of the target surface heats and evaporates it, forming eventually a plume which moves outwards from the target with high speed. The behaviour of the plume may influence the quality of the deposited layer, which is important if deposition is the goal of the process. This is particularly the case if the deposited material consists of disparate mass components. The light components move faster than the heavy ones and tend to spread on larger area of the substrate. In consequence the stoichiometry of the deposited material is not preserved. To improve the situation, the deposition process may be performed in the atmosphere of an ambient gas, which decelerates both the motion of the plume as a whole and its expansion. Deceleration is stronger for light components of the plume, which makes the expanding plume more uniform.