275 research outputs found
Focusing of laser-generated ion beams by a plasma cylinder: similarity theory and the thick lens formula
It is shown that plasma-based optics can be used to guide and focus highly
divergent laser-generated ion beams. A hollow cylinder is considered, which
initially contains a hot electron population. Plasma streaming toward the
cylinder axis maintains a focusing electrostatic field due to the positive
radial pressure gradient. The cylinder works as thick lens, whose parameters
are obtained from similarity theory for freely expanding plasma in cylindrical
geometry. Because the lens parameters are energy dependent, the lens focuses a
selected energy range of ions and works as a monochromator. Because the
focusing is due to the quasineutral part of the expanding plasma, the lens
parameters depend on the hot electron temperature only, and not their
density
Relativistic Doppler effect: universal spectra and zeptosecond pulses
We report on a numerical observation of the train of zeptosecond pulses
produced by reflection of a relativistically intense femtosecond laser pulse
from the oscillating boundary of an overdense plasma because of the Doppler
effect. These pulses promise to become a unique experimental and technological
tool since their length is of the order of the Bohr radius and the intensity is
extremely high W/cm. We present the physical mechanism,
analytical theory, and direct particle-in-cell simulations. We show that the
harmonic spectrum is universal: the intensity of th harmonic scales as
for , where is the largest --factor
of the electron fluid boundary, and for the broadband and
quasimonochromatic laser pulses respectively.Comment: 4 figure
- …