Feasibility Experiments for Underwater Shock and Bubble Generation with a High-Power Laser

摘要

High energy laser pulses (up to 150 joules at 527 nm) were directed onto underwater targets to produce a heated volume which, upon expansion, created underwater shocks and bubbles. These experiments were a feasibility study for a laboratory experimental program studying two phenomena: (1) bubble collapse dynamics in close proximity to a solid interface, and (2) shock propagation dynamics in aerated sand/water mixtures. The laser was focused both onto a point in the water and onto the surface of a solid thin foil target immersed in the water. For both types of targets, the focal volume of the laser beam was in water. Solid laser targets were observed to effectively localize laser energy deposition, providing a point shock source and producing spherical shocks. Shock pressures were inferred from shock propagation speeds to be 30 Kbar at 2 mm, and measured by carbon piezoresistive gauges to be 200 bar at 13 mm. Bubbles were formed with maximum radii of 15 mm and oscillation times of 3 ms. Key features of a design for a permanent experimental chamber are given in the report.