Abstract

During the interaction of an intense laser pulse with a solid metal target, a high temperature, high density plasma is formed. Pulsed laser ablation has attracted much interest over the past fifty years with experimental and theoretical work largely focussed on the study of laser produced plasmas in vacuum. The study of pulsed laser ablation has been largely motivated from a materials processing perspective, with the characterisation of thin films using pulsed laser deposition of particular interest. Another application resulting from the study of laser produced plasmas is the use of laser-induced breakdown spectroscopy (LIBS) for elemental composition and quantitative analysis of samples. LIBS is now a widely used technique employed in various fields including environmental analysis, forensics and biomedical applications. While much work has been carried out on pulsed ablation of materials in vacuum and gas ambient, comparatively little research has been done on ablation in liquid media. As a result, the fundamental understanding of laser produced plasmas in liquids remains insufficient. Using techniques such as time resolved imaging and spectroscopy, a full characterisation of the plasma formed in air was undertaken as a comparison to the subsequent investigation of the plasma formed in water ambient. Single pulse studies revealed information on the dynamic evolution of a laser plasma formed in the liquid phase where strong confinement and broadband emission were the main observations. Shadowgraphy measurements were performed to examine the dynamic behaviour of the cavitation bubble that eventually forms post plasma ignition. The results of time resolved optical emission measurements from within the cavitation bubble using a second laser pulse reveal for the first time the full dynamic evolution of the plasma formed in such an environment.