Title: Optimized K alpha x-ray flashes from femtosecond-laser-irradiated foils
Authors: Lu, W ×
Nicoul, M
Shymanovich, U
Tarasevitch, A
Zhou, Ping
Sokolowski-Tinten, K
von der Linde, D
Masek, M
Gibbon, Paul
Teubner, U #
Issue Date: 2009
Publisher: Published by the American Physical Society through the American Institute of Physics
Series Title: Physical Review E, Statistical, Nonlinear and Soft Matter Physics vol:80 issue:2 pages:026404 -026404
Abstract: We investigate the generation of ultrashort K alpha pulses from plasmas produced by intense femtosecond p-polarized laser pulses on Copper and Titanium targets. Particular attention is given to the interplay between the angle of incidence of the laser beam on the target and a controlled prepulse. It is observed experimentally that the K alpha yield can be optimized for correspondingly different prepulse and plasma scale-length conditions. For steep electron-density gradients, maximum yields can be achieved at larger angles. For somewhat expanded plasmas expected in the case of laser pulses with a relatively poor contrast, the K alpha yield can be enhanced by using a near-normal-incidence geometry. For a certain scale-length range (between 0.1 and 1 times a laser wavelength) the optimized yield is scale-length independent. Physically this situation arises because of the strong dependence of collisionless absorption mechanisms-in particular resonance absorption-on the angle of incidence and the plasma scale length, giving scope to optimize absorption and hence the K alpha yield. This qualitative description is supported by calculations based on the classical resonance absorption mechanism and by particle-in-cell simulations. Finally, the latter simulations also show that even for initially steep gradients, a rapid profile expansion occurs at oblique angles in which ions are pulled back toward the laser by hot electrons circulating at the front of the target. The corresponding enhancement in K alpha yield under these conditions seen in the present experiment represents strong evidence for this suprathermal shelf formation effect.
ISSN: 2470-0045
Publication status: published
KU Leuven publication type: IT
Appears in Collections:Non-KU Leuven Association publications
× corresponding author
# (joint) last author

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