Highly relativistic laser interactions with ordered nanostructures
Date
2019
Authors
Hollinger, Reed, author
Rocca, Jorge J., advisor
Prieto, Amy L., committee member
Menoni, Carmen, committee member
Marconi, Mario, committee member
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Abstract
Heating high density matter to extreme temperatures has been one of the primary motivations behind the construction of high power laser facilities around the world. The creation of simultaneously hot (multi-keV) and dense (on the order of a solid) plasma with small scale and mid-scale lasers is a difficult problem due to the barrier that the critical electron density imposes to optical lasers, typically limiting the heating to a very thin plasma into which the laser is inefficiently coupled. Experiments conducted at Colorado State University with joule level laser pulses have demonstrated that using high contrast, relativistic laser pulses it is possible to efficiently heat near solid density nanowire arrays volumetrically to multi-keV temperatures. This dissertation extends these results to the highly relativistic regime, demonstrating extremely high ionization states for volumes >5μm in depth. These relatively large volume plasmas have longer hydrodynamic cooling times while their radiative cooling time is greatly decreased due to the near solid electron densities. This results in very efficient conversion of optical laser light into x-rays since the plasma is able to radiate away more of its' energy as x-rays before cooling due to hydrodynamic expansion. With this technique, an x-ray conversion efficiency of nearly 20% was measured for photon energies greater than 1keV. After a significant upgrade to the laser, these interactions were explored at highly relativistic intensities up to 4x1021 Wcm−2, nearly 1000 times higher than initial experiments. Measurements of the energy deposition dynamics, including the time limit for energy coupling and the volume of the nanowire plasma were carried out in comparison to solid targets. The results show that at these intensities, it is possible to generate unprecedented degrees of ionization never before obtained with ultrashort pulse lasers, such as H-like Ni (27 times ionized) and Ne-like Au (69 times ionized).
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Subject
laser matter interactions
x-ray sources
nanostructures
high energy density physics