Effect of the laser focus position on characteristics of X-ray and ion emission from gold plasmas generated by a sub-nanosecond laser |
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Authors: | S Chaurasia DS Munda S Tripathi NK Gupta LJ Dhareshwar GJ Tallents |
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Affiliation: | 1. Laser and Neutron Physics Section, Bhabha Atomic Research Centre, Mumbai 400 085, India;2. Department of Physics, University of York, YO10 5DD, UK |
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Abstract: | X-ray and ion emission from gold plasma produced by a sub-nanosecond Nd:glass laser has been studies as a function of distance of the target from the best focus position. Thermal ion (kinetic energy <19 keV) signals and soft X-ray flux (photon energy >0.7 keV) measurements decrease as the target is moved closer to the best focus position in spite of an increase in laser intensity. We observe simultaneously a strong correlation between the onset of this drop in the flux of soft X-ray and the growth of harder X-ray (photon energy 3–5 keV), alongside a growth in fast ion (energy >67 keV) numbers. This is indicative of the onset of non-linear processes at the higher irradiances (~1014 W/cm2) associated with the best focus position. Our results show that when using laser plasmas as X-ray or ion sources, X-ray and ion emission in a desired spectral range can be optimized by adjusting the focusing on the target. |
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