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Damage is produced in the surface of a zinc selenide window in contact with water when pulsed laser radiation at 10.6 μm from a TEA CO2 laser is focused through the zinc selenide onto the solid-liquid interface. The damage shows strong similarities to that produced by solid particle impact on a free glass surface. The damage is believed to be due to localized loading of the zinc selenide by the high pressure in the water generated by the laser radiation absorbed at the solid—liquid boundary.

Vapour cavities in liquid flows have long been associated with cavitation damage to nearby solid surfaces and it is thought that the final stage of collapse, when a high- speed liquid jet threads the cavity, plays a vital role in this process. The present study investigates this aspect of the motion of laser-generated cavities in a quiescent liquid when the distance (or stand-off) of the point of inception from a rigid boundary is between 0.8 and 1.2 times the maximum radius of the cavity. Numerical simulations using a boundary integral method with an incompressible liquid impact model provide a framework for the interpretation of the experimental results. It is observed that, within the given interval of the stand-off parameter, the peak pressures measured on the boundary at the first collapse of a cavity attain a local minimum, while at the same time there is an increase in the duration of the pressure pulse. This contrasts with a monotonic increase in the peak pressures as the stand-off is reduced, when the cavity inception point is outside the stated interval. This phenomenon is shown to be due to a splash effect which follows the impact of the liquid jet. Three cases are chosen to typify the splash interaction with the free surface of the collapsing cavity: (i) surface reconnection around the liquid jet; (ii) splash impact at the base of the liquid jet; (iii) thin film splash. Hydrodynamic pressures generated following splash impact are found to be much greater than those produced by the jet impact. The combination of splash impact and the emission of shock waves, together with the subsequent re-expansion, drives the flow around the toroidal cavity producing a distinctive double pressure peak.

The acoustic transients associated with optical cavitation in water have been studied using a high-speed interferometric technique. Radial pressure profiles of these spherical transients have been obtained over a range between 2 and 22 mm from the centre of the cavity. Pressure-radius relationships and transient energies have subsequently been determined for the acoustic waves and the volumes of liquid enclosed within them.

A significant enhancement of the single-shot laser-induced damage threshold of CaF2 and fused silica and a moderate enhancement for GaAs and Al has been observed as the result of laser annealing using an excimer laser operating at 248 nm. This phenomenon is primarily attributed to a reduction of the residual surface roughness of the samples.