Three-dimensional hybrid optoacoustic imaging of the laser-induced plasma and deposited energy density under optical breakdown in water

Abstract

We report on a hybrid optoacoustic method aimed to retrieve the three-dimensional spatial distributions of the plasma electron density and the deposited energy density in the region of plasma formation under optical breakdown in condensed medium. The spatial distribution of the plasma electron density obtained by the proposed method with the accuracy of 3×1018 cm−3 gives the qualitative characterization of the laser pulse propagation in the region of plasma formation. The spatial distribution of the deposited energy density retrieved by the proposed method with the accuracy of 14 J/cm3 provides the quantitative description of the laser impact on the bulk of the medium. The method is based on photoacoustic imaging and shadowgraphy techniques, which have the spatial resolution of 2 μm and 10 μm, respectively. The proposed method can be applied both in the area of technological applications, such as micromachining of transparent materials, and in the field of the fundamental science of laser–matter interaction.