Time-resolved resonance shadow imaging of laser-produced lead and tin plasmas

The resonance shadowgraph technique is proposed and evaluated for the imaging of laser-produced plasmas. In this work, the shadowgraphs of lead and tin plasmas and post-plasma plumes were obtained by igniting the plasma on the surface of pure lead or tin, and illuminating the plumes using an expanded dye laser beam tuned in resonance with a strong resonance lead (283.3 nm) or tin (286.3 nm) transition. The image of the strongly absorbing plasma and post-plasma plume was then formed on a fluorescent screen placed behind the plasma, and was recorded by use of a TV camera, a video recorder, and a computer. In addition, the UV photodecomposition of lead and tin dimers or large clusters, present in the atmosphere, was visualized using this method. The evolution of the plasmas was studied at different argon pressures (from 50 to 1000 mbar). A shock wave produced by laser ablation was also observed and its speed was measured as a function of the argon pressure and the delay time between the ablating and the imaging lasers.