An effect of the target position relative to the laser focus on X-ray emission from the laser plasma

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Abstract
The first harmonics beam generated by an iodine laser system was focused by an f/2 optics on an Al foil target. The X-ray output from the laser plasma both in the line and broad-band spectra was registered over an interval around the “ideal” focus. It was found that the maximum X-ray power is not obtained in the focus itself but for a somewhat larger focal spot outside the focus. To explain this phenomena, temperature and density measurements were in addition made. The plasma temperature evaluated from both the line (He-like Al XII resonant line and j, k, l satellites) and broad-band spectra (two foil method) was also measured and found to be largely constant in the vicinity of the focus. The line and broad-band temperatures differ, the broad-band temperature being about 25% higher. The electron density was equally determined using an intercombination line.