Plasma diagnostics during laser ablation in a cavity

The formation of a laser-induced plasma in a cavity and the effects of a cavity on the ablation process were investigated. Cavities were fabricated in fused silica with equal depths and variable diameters to provide aspect ratios (depth/diameter) of 1, 3 and 6. The temperature and electron number density of the pulsed laser-induced plasma in the cavities were determined from spectroscopic measurements. Reflection and confinement effects by the cavity walls and plasma shielding were discussed to explain increased temperature and electron number density with increasing cavity aspect ratio. The temporal variations of the plasma temperature and electron number density sharply decreased inside the cavity. An adiabatic expansion model was not suitable for the laser-induced plasma in the cavity because plasma wall interactions were not included. Properties of laser-induced plasmas in the cavities and on a flat surface were compared.