Kinematics of femtosecond laser-generated plasma expansion: determination of sub-micron density-gradient and collisionality evolution of over-critical laser plasmas

G. G. Scott, G.F.H. Indorf, M.A. Ennen, P. Forestier-Colleoni, S. Hawkes, L. Scaife, M. Sedov, D. R. Symes, C. Thornton, F. Beg, T. Ma, P. McKenna, A. A. Andreev, U. Teubner, D. Neely

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Abstract

An optical diagnostic based on resonant absorption of laser light in a plasma is introduced and is used for the determination of density scale lengths in the range of 10 nm to >1 μm at the critical surface of an overdense plasma. This diagnostic is also used to extract the plasma collisional frequency, allowing inference of the temporally evolving plasma composition on the tens of femtosecond timescale. This is found to be characterized by two eras: the early time and short scale length expansion (L < 0.1λ), where the interaction is highly collisional and target material dependent, followed by a period of material independent plasma expansion for longer scale lengths (L > 0.1λ); this is consistent with a hydrogen plasma decoupling from the bulk target material. Density gradients and plasma parameters on this scale are of importance to plasma mirror optical performance and comment is made on this theme.
Original languageEnglish
Article number093109
JournalPhysics of Plasmas
Volume28
Issue number9
Early online date23 Sep 2021
DOIs
Publication statusPublished - 30 Sep 2021

Keywords

  • plasma collisions
  • plasma physics
  • plasma temperature
  • optical reflectors
  • plasma expansion
  • laser-induced plasma
  • femtosecond lasers
  • plasma diagnostics

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