Bullseye focusing of cylindrical waves at a liquid-solid interface

TL;DR

This study investigates how bullseye laser focusing of cylindrical waves on a glass substrate influences damage thresholds, combining experimental damage tests with fluid-structure interaction simulations to understand stress distributions and damage mechanisms.

Contribution

The paper introduces a novel experimental setup using bullseye laser focusing to generate and study converging cylindrical waves and compares it with single focusing, supported by simulations to analyze stress effects.

Findings

Constructive superposition of Rayleigh waves reduces damage threshold.

Largest positive stresses (~5.6 GPa) occur at 10 ns delay in bullseye focusing.

Negative stresses (~-6.4 GPa) follow positive stresses, influencing damage outcomes.

Abstract

Two 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\mm~and 96\mm~radii). We study experimentally the threshold for 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 ($\sim 5.6\,$GPa) are achieved for bullseye focusing with \dt = 10\,ns, followed by \dt= 20\,ns which corresponds to simultaneous shock wave focusing. In all these cases, the positive stresses are followed (a few nanoseconds later) by negative stresses that can reach $\sim-6.4\,$GPa.