9 research outputs found
Role of surface roughness in hard x-ray emission from femtosecond laser produced copper plasmas
The hard x-ray emission in the energy range of 30-300 keV from copper plasmas
produced by 100 fs, 806 nm laser pulses at intensities in the range of
10 W cm is investigated. We demonstrate that surface
roughness of the targets overrides the role of polarization state in the
coupling of light to the plasma. We further show that surface roughness has a
significant role in enhancing the x-ray emission in the above mentioned energy
range.Comment: 5 pages, 4 figures, to appear in Phys. Rev.
Hard X-ray and hot electron environment in vacuum hohlraums at NIF
Time resolved hard x-ray images (hv 9 keV) and time
integrated hard x-ray spectra (hv 18-150 keV) from vacuum hohlraums
irradiated with four 351 nm wavelength NIF laser beams are presented as a
function of hohlraum size and laser power and duration. The hard x-ray
images and spectra provide insight into the time evolution of the hohlraum
plasma filling and the production of hot electrons. The fraction of laser
energy detected as hot electrons (f shows correlation with both
laser intensity and with an analytic plasma filling model
Laser coupling to reduced-scale targets at NIF Early Light
Deposition of maximum laser energy into a small, high-Z enclosure in a short laser pulse creates a hot environment. Such targets
were recently included in an experimental campaign using the first four of
the 192 beams of the National Ignition Facility [J. A. Paisner, E. M.
Campbell, and W. J. Hogan, Fusion Technology 26, 755 (1994)], under
construction at the University of California Lawrence Livermore National
Laboratory. These targets demonstrate good laser coupling, reaching a
radiation temperature of 340 eV. In addition, the Raman backscatter spectrum
contains features consistent with Brillouin backscatter of Raman forward
scatter [A. B. Langdon and D. E. Hinkel, Physical Review Letters 89, 015003 (2002)]. Also,
NIF Early Light diagnostics indicate that 20% of the direct backscatter
from these reduced-scale targets is in the polarization orthogonal to that
of the incident light
X-ray flux and X-ray burnthrough experiments on reduced-scale targets at the NIF and OMEGA lasers
An experimental campaign to maximize radiation drive in small-scale
hohlraums has been carried out at the National Ignition Facility
(NIF) at the Lawerence Livermore National Laboratory (Livermore, CA,
USA) and at the OMEGA laser at the Laboratory for Laser Energetics
(Rochester, NY, USA). The small-scale hohlraums, laser energy, laser
pulse, and diagnostics were similar at both facilities but the
geometries were very different. The NIF experiments used on-axis
laser beams whereas the OMEGA experiments used 19 beams in three
beam cones. In the cases when the lasers coupled well and produced
similar radiation drive, images of x-ray burnthrough and laser
deposition indicate the pattern of plasma filling is very different
The first experiments on the national ignition facility
A first set of shock propagation, laser-plasma
interaction, hohlraum energetics and hydrodynamic experiments have been
performed using the first 4 beams of the National Ignition Facility (NIF),
in support of indirect drive Inertial Confinement Fusion (ICF) and High
Energy Density Physics