14 November 2013 A survey of laser plasma target emissions and contamination effects
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Abstract
Since the late 1990s staff at national laboratories have been studying the effects of high energy focussed laser beams [>100J] on a variety of plasma physics targets to understand the disassembly of targets and their effects on target chamber surfaces. Target geometries have included metal foils, polymer foils, metal cylinders or cones, gas bags, metal wires and complex geometries of combinations of the above. The post shot target remnants have been studied by both optical microscopy and scanning electron microscopy. The morphology of exposed targets indicated phase changes and other physical phenomena [shock, spall, crater formation and material ejection]. Pre and post weighing of the targets has been used to determine mass lost from the target. Initially most of the material distribution analysis was performed by catching target by-products with glass or silica witness plates. Spatial and image analysis of micrographs has been used to measure angular distributions of material and its form. Spectrophotometry of the exposed witness plates in the UVVis- NIR region allowed transmission spectra to be determined and the reduction of transmittance at the laser wavelengths of interest. It also allowed estimation of average debris thickness. Shrapnel size and velocity has been studied by capturing fragments in silica aerogels. One unexpected aspect of studying the witness plates was the identification of secondary emissions from solid surfaces close to the irradiated target, this showed that the near environment of the target is also important in determining overall material distributions. We have been fortunate to find interested collaborators at other UK, European and US laboratories that have brought considerable insight into target disassembly processes and palliative measures.
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James E. Andrew, "A survey of laser plasma target emissions and contamination effects", Proc. SPIE 8885, Laser-Induced Damage in Optical Materials: 2013, 88850Q (14 November 2013); doi: 10.1117/12.2027327; https://doi.org/10.1117/12.2027327
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