Energy deposition and shock wave propagation during pulsed laser ablation in fused silica cavities

Propagation of the shock wave generated during pulsed laser ablation in cavities was measured using laser shadowgraph imaging and compared with laser ablation on a flat surface. The cavities were fabricated in fused silica with the same diameter and variable depths to provide aspect ratios (depth/diameter) of 3 and 6. It was found that outside the cavity, after similar to30 ns the radius of the expanding shock wave was proportional to t(2/5), corresponding to a spherical blast wave as predicted by the Sedov-Taylor solution. The calculated pressures and temperatures of the shocked air outside of the cavities were higher than on the flat surface. The incident energy driving the shock wave outside the cavity was smaller than that on the flat surface; the greater the cavity aspect ratio, the smaller the energy supporting the shock wave. Plasma-wall interactions are discussed to explain the sharp decrease of the energy driving the shock wave outside the cavity.