The role of geometry in the generation of a shock wave by a femtosecond laser pulse

Abstract

Laser exposure at a sufficient intensity creates a shock wave (SW), propagating in the irradiated target. The process is used in many technological applications. As a result of femtosecond exposure, a warmed up layer with a thickness of d T ∼ 0.1 μm occurs. The radius of the heating spot R L varies from values of the order of a micron (focusing on the diffraction limit) up to tens or hundreds of microns depending on the experiment. As you can see, R L ≫ d T, therefore one-dimensional motion with a plane surface is generated. The quasi-plane SW stage ends when the SW moves away from the target surface to a depth of about RL. Then the stage of quasi-hemispherical propagation begins. The paper analyzes the transition from plane to hemispherical SW. The motion of the “wings” of a hemispherical wave on the target surface bordering on a gas or vacuum is investigated. Theoretical estimates and numerical simulation results are presented. Analysis of the movement of the “wings” on the surface is important for experimental diagnostics of phenomena inside the target.