Measurement and simulations of hollow atom X-ray spectra of solid-density relativistic plasma created by high-contrast PW optical laser pulses

Pikuz, S.A. and Faenov, A. and Colgan, J. and Dance, R.J. and Abdallah, J. and Wagenaars, E. and Booth, N. and Culfa, O. and Evans, R.G. and Gray, R.J. and Kaempfer, T. and Lancaster, K.L. and McKenna, P. and Rossall, A.L. and Skobelev, I. and Schulze, K.S. and Uschmann, I. and Zhidkov, A.G. and Woolsey, N.C. (2013) Measurement and simulations of hollow atom X-ray spectra of solid-density relativistic plasma created by high-contrast PW optical laser pulses. High Energy Density Physics, 9 (3). pp. 560-567. ISSN 1574-1818 (https://doi.org/10.1016/j.hedp.2013.05.008)

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Abstract

K-shell spectra of solid Al excited by petawatt picosecond laser pulses have been investigated at the Vulcan PW facility. Laser pulses of ultrahigh contrast with an energy of 160J on the targetallow studies of interactions between the laser field and solid state matter at 10W/cm. Intense X-ray emission of KK hollow atoms (atoms without n=1 electrons) from thin aluminum foils is observed from optical laser plasma for the first time. Specifically for 1.5μm thin foil targets the hollow atom yield dominates the resonance line emission. It is suggested that the hollow atoms are predominantly excited by the impact of X-ray photons generated by radiation friction to fast electron currents in solid-density plasma due to Thomson scattering and bremsstrahlung in the transverse plasma fields. Numerical simulations of Al hollow atom spectra using the ATOMIC code confirm that the impact of keV photons dominates the atom ionization. Our estimates demonstrate that solid-density plasma generated by relativistic optical laser pulses provide the source of a polychromatic keV range X-ray field of 10W/cm intensity, and allows the study of excited matter in the radiation-dominated regime. High-resolution X-ray spectroscopy of hollow atom radiation is found to be a powerful tool to study the properties of high-energy density plasma created by intense X-ray radiation.

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