Enhanced shock wave detection sensitivity for laser-produced plasmas in low pressure ambient gases using interferometry

Abstract

We report results from the analysis of the shock wave formed following the creation of a laser-produced plasma in a gaseous atmosphere, using both interferometry and shadowgraphy. A Nomarski polarization interferometer and a focused-type shadowgraphy setup were utilized to track the evolution of the shock wave with high spatial and temporal resolution for a variety of incident laser energies and ambient gas pressures. It was found that the visibility of the shock wave was high for both techniques at high gas pressure (100 mbar) and incident laser energies (400 mJ). The velocity of the shock wave in these regimes was of the order of several km s −1. At lower pressures (≈ 1-10 mbar) and incident laser energies (≈ 100-200 mJ), the visibility of the shock wave decreased dramatically and, in some cases, disappeared completely from the shadowgrams. In contrast, the shock wave remained visible in the interferograms, manifesting itself as a blurring of the fringes. The shock wave visibility was improved further by simply differentiating the interferograms to enhance the fringe boundaries. Shock velocities, exceeding 100 km s −1 , were detected at low background gas pressures where the enhanced shock wave visibility was provided by the interferometer.

Significance of ambient conditions in uranium absorption and emission features of laser ablation plasmas

“…Persistence generally increases with increasing system pressure because the plasma expansion rate decreases logarithmically with increasing pressure. Hence emission is confined to a location axially closer to the target surface where plasma temperatures are typically greater than if the plasma is allowed to expand in vacuum-like conditions (or low pressures) [38][39][40]. Therefore, at an axial distance of ~1.5 mm from the target surface, the emission persistence appears greater at higher pressures.…”

Spatial Molecular AlO Temperature Distributions in Laser-Induced Plasma

“…Namely, multiple temperature gradients exist which correspond to the leading/following edges of the plasma blast wave. Further insight into the shockwave interaction with the plasma material may be obtained by coupling the radial deconvolution analysis with shockwave imaging studies, such as shadowgraph or schlieren techniques, or interferometric methods [28,29]. The purpose of such a study would be to elucidate the affect of the plasma shockwave on the chemical kinetics of the plasma plume expansion into ambient atmospheres.…”

Spatial Molecular AlO Temperature Distributions in Laser-Induced Plasma

“…Further insight into the shockwave interaction with the plasma material may obtained by coupling the radial deconvolution analysis with shockwave imaging studies, such as shadowgraph or schlieren techniques, or interferometric methods [28,29]. The purpose of such a study would be to elucidate the affect of the plasma shockwave on the chemical kinetics of the plasma plume expansion into ambient atmospheres.…”