Bullseye focusing of cylindrical waves at a liquid–solid interface

Abstract

Two pairs of converging and superimposing shock and Rayleigh waves are generated on a glass substrate by focusing laser pulses on two concentric rings in a bullseye configuration (67 and 96 μm radii). We experimentally study the threshold for the substrate damage as a function of the number of repetitions and the delay (0–20 ns). The bullseye focusing experiments are compared to a single focusing ring. Additionally, fluid–structure interaction simulations using a volume-of-fluid framework are utilized to estimate the stresses. The lowest number of repetitions to attain surface damage is found for constructive superposition of the Rayleigh waves, i.e., here for a delay of 10 ns. The observed damage is consistent with the simulations where the largest positive stresses (∼5.6 GPa) are achieved for bullseye focusing with Δt=10 ns followed by Δt=20 ns, which corresponds to a simultaneous shock wave focusing. In all these cases, the positive stresses are followed (a few nanoseconds later) by the negative stresses that can reach ∼−6.4 GPa.